Abstract
Olfactory cues may influence host plant preferences for oviposition of female moths within a community of stemborers that utilise the same resource. This study aimed to evaluate plant preferences for oviposition of gravid females of noctuid stemborers, Busseola fusca and Sesamia calamistis, and the crambid Chilo partellus for uninfested maize plants and plants infested by conspecific or heterospecific larvae. The involvement of volatile organic compounds (VOCs) emitted by uninfested and maize plants infested by conspecific or heterospecific larvae on moth orientation was studied in Y-tube olfactometer assays and in the field. All gravid female moths significantly preferred VOCs emitted by plants infested by conspecific or heterospecific larvae over those from uninfested plants, and female moths did not systematically prefer VOCs emitted by plants infested by conspecifics. Field trials confirmed these results. Chemical analysis by coupled gas chromatography/mass spectrometry showed that VOCs emitted by larvae-infested plants, regardless of the stemborer species, were compositionally richer than those released by uninfested plants but their emission intensity varied with species involved in the infestation. Busseola fusca larvae induced a compositionally richer VOCs profile than S. calamistis and C. partellus larvae. Eight candidate attractants were associated with larvae-infested plants. These results open new avenues to develop attractants specific to trap female stemborer moths in the field.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Introduction
Direct and indirect interactions between species maintain the structure and function of ecological communities (Wootton and Emmerson 2005). Often, these interactions occur through the same resource utilisation by phytophagous insects. Its outcome can be negative (e.g. competition), positive (e.g. facilitation) or neutral (Kaplan and Denno 2007; Speight et al. 2008). These interactions can be directly intraspecific or interspecific (Memmott et al. 2007) or indirectly through the mediation of the same host plant (Fisher et al. 2000; Kaplan and Denno 2007). The interactions among species can influence the oviposition preferences of gravid females utilising the same host plant in a community (Craig et al. 2000; Shiojiri et al. 2002). Thus, competition for or facilitation in the use of the same resource can influence the final choice by the female for oviposition. For example, prior feeding of larvae on a plant induces female oviposition on that plant in some cases (Anderson and Alborn 1999; Craig et al. 2000; Facknath 2012; Groot et al. 2003; Viswanathan et al. 2005, 2015), while in other cases, this deters subsequent oviposition (De Moraes et al. 2001; Sato et al. 1999; Fatouros et al. 2012; Wise and Weinberg 2002). Constitutive and inductive plant volatile chemicals have been identified to play an important role in host plant selection by phytophagous insects for food or oviposition (Dicke and Van Loon 2000; Honda 1995). The infochemicals from infesting stages (eggs or larvae) from other conspecifics have been shown to influence gravid female oviposition choice, which serves to adjust population sizes to available resources with, in general, a preference for uninfested plants (Maclellan 1962; Rothschild and Schoonhoven 1977).
The lepidopteran species Busseola fusca (Fuller) (Noctuidae), Sesamia calamistis Hampson (Noctuidae) and Chilo partellus (Swinhoe) (Crambidae) are among the main pests of cereals in sub-Saharan Africa (Kfir et al. 2002). Because of the cryptic habit of their larval stages to feed in plant stems, these species are referred to as stemborers. In East and Southern Africa, where they co-exist, they occur as communities of single or mixed species infesting not only cereal crops in the fields (Krüger et al. 2008; Ong’amo et al. 2006a, b), but also wild graminaceous plants (Le Ru et al. 2006; Moolman et al. 2014). The composition of these stemborer communities varies with locality, altitude and season. For example, in Kenya, B. fusca is the dominant species in the highlands, while C. partellus dominates in the lowlands. Sesamia calamistis is present at all altitudes in low numbers. In the mid-altitudinal regions, the stemborers occur as a mixed community of the three species, but with variation in species dominance with respect to locality, season and year (Guofa et al. 2001; Ong’amo et al. 2006a, b). In parts of Southern Africa C. partellus occurs in mixed populations with B. fusca in both the highland (Bate and Van Rensburg 1992; Van Rensburg and Van den Berg 1992; Ebenebe et al. 1999) and lowland regions (Cugala and Omwega 2001; Krüger et al. 2008) but the dominance of a species might vary with environment. Under laboratory studies, both intra- and interspecific competitions were observed between the three species with stronger interspecific competition for food resource utilisation recorded between the two noctuids and the crambid than between the two noctuids (Ntiri et al. 2016). Additionally, ovipositing females prefer maize plant previously infested by larvae over uninfested plants suggesting a strong relation between larval feeding and female oviposition choice (Ntiri et al. 2018). These results indicated that maize plants infested by conspecifics or heterospecifics produce or elicit chemical signatures rendering the plants more attractive to female moths.
Olfaction plays a major role in insect–plant interactions and this has been extensively investigated (e.g. Giunti et al. 2016; Trematerra et al. 2007). Nevertheless, the impact of olfactory cues shaping the relationships among insects from the same guild competing for shared resources, mostly in hetero-specific interaction for oviposition site, is poorly explored. For instance, signals left by closely related species, as oviposition and host-marking pheromones, may be exploited by herbivores to detect competitor activity (Steidle et al. 2005; Ukeh et al. 2012). In this scenario, the prompt recognition of unsuitable or harmful habitats by host-seeking insects is critical for their survival and fitness. As such, semiochemicals emitted by infested plants could be exploited by host-seeking insects to avoid competition. On the other hand, for some insect species such cues rather elicit responses which indicate attractiveness (e.g. Agrawal and Sherriffs 2001; Horgan 2012).
Here, we focused on the olfactory responses of the gravid females of B. fusca, S. calamistis and C. partellus to maize plant odours infested by conspecific and heterospecific larvae, and to uninfested plants. First, we evaluated the attractiveness of each species to uninfested and maize plants infested by either B. fusca, S. calamistis or C. partellus larvae. Second, we also compared the preference of odours emitted between plants infested by either B. fusca, S. calamistis or C. partellus larvae. Third, we linked these results to the levels of volatile organic compounds (VOCs) from uninfested and larvae-infested maize plants captured by both dynamic headspace and Solid Phase MicroExtraction (SPME) techniques and analysed through gas chromatography/mass spectrometry (GC/MS).
Methods and materials
Plants and insects
Maize plants of hybrid H513 (Simlaw, Kenya Seed Company, Nairobi, Kenya) were grown in plastic pots (12 cm in height × 13 cm in diameter) in a greenhouse at the Duduville campus of the International Centre of Insect Physiology and Ecology, (icipe) Nairobi, Kenya. Mean temperatures were approximately 31/17 °C (day/night) with a L12:D12 photoperiod. Plants were used in experiments when they were between 4 and 6 weeks old, i.e. about 60–75 cm.
Because wild insects are more responsive to plant odours compared to laboratory-reared insects, as shown for B. fusca (Calatayud et al. 2008), only field-collected insects of B. fusca (Bf), S. calamistis (Sc) and C. partellus (Cp) were used in the Y-tube experiments. For each species, fourth to fifth instar larvae were collected from maize fields. They were then reared until pupation on the artificial diet of Onyango and Ochieng’-Odero (1994) for B. fusca and S. calamistis and on the artificial diet of Ochieng et al. (1985) for C. partellus. Pupae were sexed according to the method described by Underwood (1994) and males and females were kept separately in plastic containers (21 × 15 × 8 cm) until adult emergence. A cotton pad moistened with water was placed inside the container to maintain relative humidity at > 80%. The insects were kept in a rearing room at a temperature of 25 ± 0.05 °C, RH of 58.5 ± 0.4% and a photoperiod of L12:D12.
Emerged adult males and females of each species were put together in a mating cage (40 × 40 × 63 cm), at the onset of the scotophase. The mating status was checked at hourly intervals until end of the scotophase. Pairs of moths that were mating were collected in plastic jars (8 cm high × 5 cm in diameter). The gravid females were used in experiments on the following night. After each experiment, all females used were dissected to check for the presence of spermatophores in the bursa copulatrix, which in Lepidoptera indicates successful mating (Lum 1979). Only females bearing spermatophores were considered in the results. For plant infestations, larvae of B. fusca, C. partellus and S. calamistis were obtained from colonies reared at the Animal Rearing and Containment Unit (ARCU) at icipe, Nairobi, Kenya. All colonies were rejuvenated twice a year with field-collected larvae.
Plant infestations
For each stemborer species, single maize plants were manually infested by putting them in the whorl with 12 (for Y-tube experiments) or 5 (for field experiments) third and fourth instar larvae, the larval stages which can co-occur with adult moths in the field (Le Ru B. & Calatayud P.-A., Pers. Observ.). These larval stage and infestation level were chosen to ensure a high degree of feeding damage within 24 h before start of the experiments. Because of the long duration of the field experiments, the number of larvae used for infestation had to be lower to ensure survival of the maize plants.
Olfactometer bioassays
This experiment was carried out in a Y-tube olfactometer (Ngi-Song et al. 1996), which has been shown to be more useful for demonstrating differences in attration to odours in moths than wind tunnel (Calatayud et al. 2014). Similarly to Petit et al. (2018), it had the following dimensions: length of stem (18 cm); length of each arm (34 cm); diameter (4 cm). Observations were performed 0–4 h after onset of the scotophase for females corresponding to the period of oviposition for the species under study (Calatayud et al. 2007). The pot and soil of each potted plant (1 plant per pot) were wrapped with aluminium foil to prevent the introduction of volatiles from the plastic pot and soil into the Y-tube. Each plant was introduced into a Perspex chamber measuring 30 × 30 × 120 cm large enough to contain the whole potted plant. The closed ends of each chamber were connected with Teflon tubing to either of the two arms of the Y-tube. Clean air was drawn into the system over the sample through the arms of the olfactometer. The airflow was set at 15 cm s−1 per arm and measured by flow meters connected between the chambers and the activated charcoal. For 30 min before each test, air was left flowing through the olfactometer setup to reach equilibrium in the two chambers and the Y-tube. The Y-tube experiments were carried out at 25 ± 2 °C and 50–60% RH. To avoid visual cues, all the experiments were carried out in a dark room illuminated with red fluorescent tubes (20 W). For each stemborer species, gravid females were released individually into the base of the Y-tube placed horizontally on the table and allowed to choose either of the two arms. The duration of a single evaluation was a maximum of 10 min. For each species, the following choice combinations were done: uninfested maize vs empty chamber; uninfested maize vs maize infested by either B. fusca, S. calamistis larvae or by C. partellus larvae. To assess interactions among insects, the following choice combinations were offered to each species: maize infested by B. fusca larvae vs maize infested by S. calamistis larvae; maize infested by B. fusca larvae maize vs maize infested by C. partellus larvae; maize infested by S. calamistis larvae maize vs maize infested by C. partellus larvae. For each test, a choice was recorded when the insect passed 5 cm from the intersection into one arm and remained motionless there for more than 20 s. Those that made no choice were also recorded. After every five insects, odour source connections to the chambers were reversed to minimise any location bias and the chambers were cleaned thoroughly with normal water. In each case, the number of gravid females ranging from 20 to 37 were tested (n = 20–37). For each conditioning procedure, the percentage of insects that made a distinct choice was calculated.
Field trials
Field trials were carried out to check if caterpillar-induced volatiles attract con- and hetero-specific wild moths for oviposition under field conditions in Makutano (S 0°43.616, E 37°16.373) where C. partellus and S. calamistis are the most abundant species and in Murang’a (S 0°55.387, E 37°09.004), where B. fusca and S. calamistis co-infest maize fields, (Ntiri 2015). The Murang’a and Makutano areas in central region of Kenya are intensively maize cultivated regions situated at 1500 and 1150 m asl, respectively. Annual mean rainfall is 1195 mm and 981 mm, mean annual temperatures 20 °C and 21.2 °C, respectively, whereas mean annual relative humidity ranges from 50 to 72%, respectively. Six farmer fields (3 in Murang’a and 3 in Makutano) were selected for the experiment, and in each field, maize plants were grown in pots (12 cm in height x 13 cm in diameter) inside a cage (2 × 2 × 2 m) covered with a net to avoid natural infestations. The plants used in the experiments were between 4 and 6 weeks old, i.e. about 60–75 cm high.
For each species, five potted maize plants were each infested with 5 of 3rd instar larvae and individually protected with a small cage (90 cm in height × 33 cm in diameter) equipped with a one-way drawstring mesh cloth bag to limit the larval escape to the plant on which the larvae have been deposited, 24 h prior to their exposure to the field to guarantee sufficient feeding damage. Each field consisted of treatments replicated five times (i.e. for each species 5 potted plants plus 5 uninfested plants as control). The treatments were distributed along a straight line in each field in a random pattern. Then, each mesh cloth bag over each plant was removed and after one week, egg laying from wild moths as well as the remaining larvae (for infested plant) was checked on each potted plant and the number of egg batches as well as the numbers of eggs per batch were recorded. Thereafter, oviposited eggs collected were transferred in the laboratory for hatching to confirm species identity. In parallel, three pheromone traps (Pherobank BV, Wageningen), one for each of the three species (B. fusca, S. calamistis and C. partellus) were also placed in nearby fields at a height of 1.5 m from the ground to monitor the male moth flight activity period of each stemborer species in the trial fields. The experiment was conducted from April to July 2017 corresponding the long rainy season (i.e. maize cultivation). During that period, a total of 16 replicates have been conducted at Makutano and 13 replicates at Murang’a.
Collection of VOCs
Dynamic headspace
VOCs emitted from un-infested maize plants and plants infested with 5 and 12 larvae were collected by using a dynamic headspace sampling system as described by Fombong et al. (2016). Two blanks (odours collected from empty oven bags) were collected to verify the absence of background. The soil in the pot was covered with aluminium foil to avoid odour emitting from the soil. The plant was covered with oven bags (520 × 580 mm) and equipped with a valve by which charcoal-purified air entered the system at 0.5 L/min. Volatiles were collected from the plants by passing the outlet air through a Super-Q filter (50 mg adsorbent) at a rate of 2 L/min. Before use, the Super-Q filter was cleaned using hexane, dried and placed in aluminium foil to avoid any contamination. After each collection, the volatiles were eluted from the traps with 150 µL of hexane and concentrated to 40 µL under a stream of nitrogen to enable detection of compounds that are present in very trace amounts when carrying out GC-MS analysis. To the 40 µL concentrated, 10 µL of the internal standard (heptadecane) concentrated at 4 ng µL−1 was added and immediately injected into a gas chromatograph (GC) for analysis or stored at − 80 °C before analyses. VOCs were collected for 12 h (from 6:00 p.m. to 6:00 a.m.). Five plant headspace replicates were carried out in each case.
Solid phase microextraction (SPME)
VOCs emitted from uninfested and infested maize plants with 12 larvae were collected by placing a solid phase microextraction (SPME) fiber in a 20 × 20 × 120 cm glass chamber with these plants. The open end of the cylinder was capped using aluminium foil. The cylinder cap was fortified using Parafilm to make it airtight. The SPME septum-piercing needle was driven through a self-sealing, gas-tight septum (sandwiched between the foil cap) into the plant headspace. Before use, SPME fibers (DVB/CARBOXEN/PDMS 50/30 l m, Supelco) were cleaned by heating in a gas chromatograph injector at 250 °C for 20 min. About 195 µg of heptadecane was injected into the cylinder as internal standards and left to equilibrate for 10 min. Extraction of VOCs was carried out for a period of two hours per sample, and then the fibre was retracted from the headspace and immediately introduced into a gas chromatograph (GC) injector port for analysis or stored at − 80 °C before analyses. Four plant headspace replicates were carried out for each case.
Analyses of VOCs
After volatile collection, the eluates were analysed using coupled gas chromatography-mass spectrometry (GC–MS) on an Agilent Technologies 7890B GC linked to a 5977 MS, equipped with a non-polar HP-5 MS ultra-inert column (30 m × 0.25 mm i.d., 0.25 µm) (J&W, Folsom, CA, USA). The temperature program was 5 min at 35 °C, then 10°C/min to 280 °C. A 1-µl aliquot of each volatile extract was analysed in the splitless mode using helium as a carrier gas at a flow rate of 1.2 ml/min. Spectra were recorded at 70 eV in the electron impact (EI) ionization mode. Similar to Leppik and Frérot (2014), compounds were identified by comparison of mass spectral data with library data: (Adams terpenoid/natural product library 1995), (National Institutes of Standards and Technology 2008) and ChemStation data system (G1701EA, version E.02.00). Furthermore, structure assignments of a fraction of each compound were confirmed based on co-injection with commercially authentic standards. These compounds included: Anisole (purity ≥ 98%), β-Bisabolene (purity > 85%), Butyl butanoate (purity 98%), (E)-Caryophyllene (purity ≥ 80%), α-Cedrene (purity ≥ 95%), (E)-β-Farnesene (purity ≥ 90%), (Z)-3-Hexenyl acetate (purity ≥ 98%), (E)-3-Hexenyl acetate (purity ≥ 98%), Indole (purity ≥ 99%), Linalool (purity 96%), (R)-(+) Limonene (purity ≥ 95%), Methyl salicylate (purity ≥ 99%), Myrcene (purity 98%), n-Nonanal (purity 95%), (S)-(−) α-Pinene (purity 99%), Sabinene (purity 99%), γ-Terpinene (purity 97%), Thymol (purity 99%) and α-Zingiberene (purity ≥ 99%). All the standards compounds were purchased from Sigma-Aldrich Chemical Company except α-Zingiberene which was purchased from Santa Cruz Biotechnology.
The VOC peak area information was extracted from the raw GC/MS data and transformed into nanograms (ng) using internal standard peak area. The relative amount of each compound was calculated by dividing the overall weight of the compound (ng) by the sum of the detected compounds from the same analysis and expressed as percentages and calculated as the mean ± standard error.
Statistical analyses
All analyses were carried out in R version 3.4.1 (R Core Team 2017). The number of responding gravid female obtained from the dual choice olfactometer assays were recorded as the number of gravid females that responded to the different treatments and expressed as per cent response [(n/N) × 100]; N corresponds to the total number of responding gravid females, while n is the number of gravid females corresponding to a given treatment. The proportions of the females that did a choice from the dual choice olfactometer assays were analysed by Chi square goodness of fit performed at 5% significance level. From the field trials, the proportions of males captured between pheromone lures were compared using the Tukey Kramer’s test. The total number of egg batches oviposited by wild moths recovered on uninfested potted plants was compared to the total number of egg batches recovered on infested plants using the Fisher’s exact test. For chemicals, before statistical comparisons of VOCs between plants status, all data were checked for normality and homogeneity of variance using Shapiro–Wilk and Bartlett tests, respectively. A non-parametric Kruskal–Wallis test was initially used to show differences of VOCs emitted between uninfested and infested plants as well as between infested plants, and Dunn’s test (a non-parametric post-hoc test for unpaired data) to discriminate the means. Principal Component Analysis (PCA) was then performed on relative amount values of each VOCs using the R package, Factoextra. This allowed us to assess how the proportions of the VOCs were distributed between uninfested and infested plants, as well as between stemborer species among infested plants. Mann–Whitney U Test was used to show the significant differences of VOCs emitted by the density of 5 and 12 larvae feeding upon the plant.
Results
Olfactometer bioassays
In the Y-tube olfactometer, 78–95% of the females made a choice in the dual-choice biossays (Figs. 1, 2, 3). Regardless of the species, all females oriented significantly towards maize plant volatiles as compared to blanks (Fig. 1), and they had a significant preference for plants infested by the same or another species over uninfested plants (Fig. 2). By contrast, female orientation under interspecific dual choices depended on the species (Fig. 3). Busseola fusca did not discriminate the odours from plants infested by noctuids (comparison B. fusca vs S. calamistis infested plants: χ2 = 1.384, df = 1, P > 0.05) but preferred odours of plants infested by their conspecifics over plants infested by C. partellus (comparisons C. partellus vs B. fusca infested plants: χ2 = 5.143, df = 1, P = 0.023). Sesamia calamistis oriented preferably towards plants infested by their conspecifics in a choice involving only noctuids (comparisons B. fusca vs S. calamistis infested plants: χ2 = 6.368, df = 1, P = 0.011) but it preferred plants infested by B. fusca over plants infested by C. partellus (comparisons C. partellus vs B. fusca infested plants: χ2 = 9.80, df = 1, P = 0.001).
Chilo partellus did not discriminate between plants infested by B. fusca and plants infested by their conspecifics (comparisons B. fusca vs C. partellus infested plants: χ2 = 0.615, df = 1, P > 0.05) but it preferred conspecifics over S. calamistis (comparisons S. calamistis vs C. partellus infested plants: χ2 = 4.545, df = 1, P = 0.033) and plants infested by S. calamistis over B. fusca (comparisons B. fusca vs S. calamistis infested plants: χ2 = 7.347, df = 1, P = 0.006).
Field trials
In each field, ~ 2 to 3 larvae of each stemborer species remained per infested potted plant. The number of male moths captured inside pheromone traps differed significantly between species and site (Table 1). Busseola fusca was absent in Makutano while C. partellus was absent in Murang’a. Therefore, no eggs of B. fusca were found on potted maize plants in Makutano, and no eggs of C. partellus in Murang’a. In Makutano, although few C. partellus males were trapped as compared to S. calamistis, both S. calamistis and C. partellus eggs were laid on potted plants. In Murang’a, significantly higher numbers of B. fusca males were trapped than S. calamistis males and eggs of both species were found on potted plants. In total, 21 and 19 egg batches of wild moths were collected in Makutano and in Murang’a, respectively. For each locality, significantly more egg batches were collected on infested than uninfested plants (Table 1).
Identification of VOCs on uninfested and infested plants
From mass spectral data comparisons between GC/MS compounds with library data and from co-injection procedure with commercially authentic standards, a total of 42 compounds were tentatively identified and found to be emitted from both uninfested and infested maize plants consisting of sesquiterpenes, monoterpenoids, green leaf volatiles, cyclic hydrocarbons and alkaloids. A total of 34 compounds were identified using the dynamic collection system, whereas 24 compounds were identified with the SPME collection system (Fig. 4) (Supplementary Tables S1 and S2). 22 VOCs were produced by all maize plants tested, whereas 20 VOCs were only emitted by infested plants irrespective of the stemborer species involved (Fig. 4).
The mean ratios of some VOCs varied significantly between uninfested and infested plants irrespective of the stemborer species. Both collection systems yielded higher amounts of α-pinene, n-nonanal, 7-epi-sesquithujene and butyl butanoate from uninfested than infested plants (Supplementary Tables S1, S2 & Fig. 5), while greater amounts of (E)-2-hexenal, 4,8-Dimethyl-1,3-(Z),7-nonatriene, (E)-caryophyllene were emitted by infested plants irrespective of the stemborer species (Supplementary Tables S1 & S2).
However, there were differences in the compounds between insect species infesting the plant (Fig. 5). With both collection systems, B. fusca larvae induced the compositionally richest VOCs profile, followed by both S. calamistis and C. partellus larvae. (E)- β-Farnesene, linalool, myrcene and β-bisabolene were characteristics to VOCs emitted by plants infested by B. fusca only, whereas α-zingiberene, sesquisabinene, indole and α-cis-bergamotene were characteristics of VOCs emitted by plants infested by C. partellus or S. calamistis (Supplementary Tables S1, S2 & Fig. 5).
VOCs with increasing larval density
Irrespective of the stemborer species most of the VOCs detected from plants infested with 5 larvae were also detected in plants infested with 12 larvae (Supplementary Table S3). Among the 34 VOCs identified using the dynamic collection system, all were found with both larval densities and 9 varied significantly with larval density (Supplementary Table S3). Among them, linalool, indole, α-cedrene, sesquisabinene, (E)-β-farnesene and α-zingiberene increased while α-pinene, n-nonanal and 7-epi-sesquithujene decreased with the larval density, irrespective of the stem borer species.
Discussion
In the Y-tube olfactometer bioassays gravid females of the three stemborer species oriented preferably towards odours emitted by plants infested by both con- and hetero-specific larvae over odours emitted by uninfested plants. Field trials confirmed these results. These findings, though contrasting with the fundamental concept of competition, have been shown for several other lepidopteran phytophagous insects (e.g. Anderson and Albron 1999; Shiojiri et al. 2002; Poelman et al. 2008; Facknath 2012; Viswanathan et al. 2015). Enhancements of oviposition by C. partellus on maize plants infested with conspecific larvae have already been reported by Kumar (1986). In addition, under interspecific choices, although the results are not conclusive enough to warrant a general interpretation, our Y-tube experiments showed that the female moths did not orient systematically preferably towards the plant infested by conspecific larvae. Our findings suggest an adaptive behaviour that may help ovipositing stemborer females to identify plants suitable for survival of their offsprings.
Herbivore feeding often modifies the volatile profiles emitted by plants (Honda 1995; Dicke and Van Loon 2000; El-Sayed et al. 2016). The common volatiles identified in the present study were previously reported by Birkett et al. (2006), Khan et al. (2000) and Konstantopoulou et al. (2004) from uninfested maize plant and by Carroll et al. (2006), Gouinguené et al. (2001) and Peñaflor et al. (2011) from infested plants. However, in the present study, the volatile profile partly depended on the collection method. In the dynamic system more VOCs were collected than in the SPME system. Similarly, Elmore et al. (1997) reported that the dynamic headspace method extracted a greater number of volatile compounds from the same samples than did SPME. This can be explained by several factors in SPME collection system such as the need to be in the linear range of detection and the competition effects on the fiber between volatiles which can cause biases in the quantitative and qualitative determination of compounds (Jelen et al. 1998; Roberts et al. 2000).
Both methods showed a higher number of volatiles emitted by infested maize plants than uninfested ones irrespective of the stemborer species involved, a phenomenon already reported by several studies (e.g. Dicke and Van Loon 2000; Ngi-Song et al. 2000; Pare and Tumlinson 1999). Some of these caterpillar-induced volatiles, which can either be produced de novo by the plant, as an indirect defence, as well as directly excreted by the larvae inside the plants, have also been reported in other studies (e.g. De Moraes et al. 2001; Kessler and Baldwin 2001; Pinto-Zevallos et al. 2016). Our results indicate that all the odour sources of infested plants were innately attractive to the female of the species tested. Giunti et al. (2018), Kumar (1986) and Poelman et al. (2008) also demonstrated that infested plants attracted and increased fitness of other conspecific species.
However, there were quantitative variations in the VOCs emitted by maize plants irrespective of the stemborer species involved in the infestation. The two collection systems revealed that the VOC profiles emitted by plants infested by B. fusca were very distinct and compositionally richer in VOC profile to those emitted by plants infested by both S. calamistis and C. partellus. Two elicitors in the oral excretion of larvae, volicitin and β-glucosidase, have been identified as being responsible for the induction of specific volatiles from plants they attack, which are different from intact or mechanically damaged plants (Dicke and Van Loon 2000; Gouinguené et al. 2001; Mattiacci et al. 1994). Thus, the type of elicitors specific to the different stemborer larval species may be responsible for these variations in HIPVs by the different stemborer species. This has been adequately established in other herbivore species (Dicke 2000; Geervliet et al. 1997; Takabayashi et al. 1994).
In addition, the intensity of caterpillar-induced VOCs depended on the larval density thus, as shown by Skoczek et al. (2017), on the extent of plant feeding damage or the amount of plant tissue consumed. Similarly, Gouinguené et al. (2003) found a correlation between the intensity of the HIPV emission and the number of Spodoptera littoralis (Boisduval 1833) (Lepidoptera, Noctuidae) larvae feeding on a plant and with the amount of damage inflicted. In the present study, the VOCs which decreased with larval density were those characteristic of uninfested plants while the VOCs which increased with larval density were those characteristic of infested plants. However, all VOCs characteristic of infested plants were found in both larval densities.
In conclusion, our results indicate that VOCs influence interactions between members of the same guild and thus might play an attractiveness role in the coexistence among maize stemborers. Eight candidate attractants were associated with larvae-infested plants that attracted conspecific and heterospecific females. These results open new avenues to develop attractants specific to trap female stemborer moths in the field.
References
Adams2 terpenoid/natural product library, AR (1995) Identification of essential oil components by gas chromotography/mass spectrometry, Allured, Carol Stream
Agrawal AA, Sherriffs MF (2001) Induced plant resistance and susceptibility to late-season herbivores of wild radish. Ann Entomol Soc Am 94:71–75. https://doi.org/10.1603/0013-8746(2001)094%5B0071:IPRAST%5D2.0.CO;2
Anderson P, Alborn H (1999) Effects on oviposition behaviour and larval development of Spodoptera littoralis by herbivore-induced changes in cotton plants. Entomol Exp Appl 92:45–51. https://doi.org/10.1046/j.1570-7458.1999.00523.x
Bate R, Van Rensburg J (1992) Predictive estimation of maize yield loss caused by Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) in maize. S. Afr J Plant Soil 9:150–154. https://doi.org/10.1080/02571862.1992.10634619
Birkett MA, Chamberlain K, Khan ZR, Pickett JA, Toshova T, Wadhams LJ, Woodcock CM (2006) Electrophysiological responses of the lepidopterous stemborers Chilo partellus and Busseola fusca to volatiles from wild and cultivated host plants. J Chem Ecol 32:2475–2487. https://doi.org/10.1007/s10886-006-9165-1
Calatayud PA, Guénégo H, Le Rü B, Silvain JF, Frérot B (2007) Temporal patterns of emergence, calling behaviour and oviposition period of the maize stemborer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae). Ann Soc Entomol Fr 43:63–68. https://doi.org/10.1080/00379271.2007.10697495
Calatayud PA, Juma G, Njagi PGN, Faure N, Calatayud S, Dupas S, Le Rü B, Magoma G, Silvain JF, Frérot B (2008) Differences in mate acceptance and host plant recognition between wild and laboratory-reared Busseola fusca (Fuller). J Appl Entomol 132:255–264. https://doi.org/10.1111/j.1439-0418.2007.01261.x
Calatayud PA, Ahuya P, Le Rü B (2014) Importance of the experimental setup in research on attractiveness of odours in moths: an example with Busseola fusca. Entomol Exp Appl 152:72–76. https://doi.org/10.1111/eea.12201
Carroll MJ, Schmelz EA, Meagher RL, Teal PEA (2006) Attraction of Spodoptera frugiperda larvae to volatiles from herbivore-damaged maize seedlings. J Chem Ecol 32:1911–1924. https://doi.org/10.1007/s10886-006-9117-9
Craig TP, Itami JK, Shantz C, Abrahamson WG, Horner JD, Craig JV (2000) The influence of host plant variation and intraspecific competition on oviposition preference and offspring performance in the host races of Eurosta solidaginis. Ecol Entomol 25:7–18. https://doi.org/10.1046/j.1365-2311.2000.00226.x
Cugala D, Omwega C (2001) Cereal stemborer distribution and abundance, and introduction and establishment of Cotesia flavipes Cameron (Hymenoptera: Braconidae) in Mozambique. Int J Trop Insect Sci 21:281–287
De Moraes CM, Mescher MC, Tumlinson JH (2001) Caterpillar-induced nocturnal plant volatiles repel conspecific females. Nature 410:577–579. https://doi.org/10.1038/35069058
Dicke M (2000) Chemical ecology of host-plant selection by herbivorous arthropods: a multitrophic perspective. Biochem Syst Ecol 28:601–617. https://doi.org/10.1016/S0305-1978(99)00106-4
Dicke M, Van Loon JJA (2000) Multitrophic effects of herbivore-induced plant volatiles in an evolutionary context. Entomol Exp Appl 97:237–249. https://doi.org/10.1046/j.1570-7458.2000.00736.x
Ebenebe A, Van den Berg J, Van der Linde TDK (1999) Distribution and relative abundance of stalk borers of maize and grain sorghum in Lesotho. Afr Plant Prot 5:77–82
Elmore JS, Erbahadir MA, Mottram DS (1997)) Comparison of dynamic headspace concentration on Tenax with solid-phase microextraction for the analysis of aroma volatiles. J Agric Food Chem 45:2638–2641. https://doi.org/10.1021/jf960835m
El-Sayed AM, Knight AL, Byers JA, Judd GJR, Suckling DM (2016) Caterpillar-induced plant volatiles attract conspecific adults in nature. Sci Rep 6:37555. https://doi.org/10.1038/srep37555
Facknath S (2012) Study of herbivore response to the presence of conspecifics and heterospecifics in an insect-host plant relationship. Univ Mauritius Res J 18B:250–274
Fatouros NE, Lucas-Barbosa D, Weldegergis BT, Pashalidou FG, van Loon JJA, Dicke M, Harvey JA, Gols R, Huigens ME (2012) Plant volatiles induced by herbivore egg deposition affect insects of different trophic levels. PLoS One 7 e43607. https://doi.org/10.1371/journal.pone.0043607
Fisher AEI, Hartley SE, Young M (2000) Direct and indirect competitive effects of foliage feeding guilds on the performance of the birch leaf-miner Eriocrania. J Anim Ecol 69:165–176. https://doi.org/10.1046/j.1365-2656.2000.00384.x
Fombong AT, Mutunga JM, Teal PEA, Torto B (2016) Behavioral evidence for olfactory-based location of honeybee colonies by the scarab Oplostomus haroldi. J Chem Ecol 42:1063–1069. https://doi.org/10.1007/s10886-016-0748-1
Geervliet JBF, Posthumus MA, Vet LEM, Dicke M (1997) Comparative analysis of headspace volatiles from different caterpillar-infested or uninfested food plants of Pieris species. J Chem Ecol 23:2935–2954. https://doi.org/10.1023/A:1022583515142
Giunti G, Benelli G, Conte G, Mele M, Caruso G, Gucci R, Flamini G, Canale A (2016) VOCs - Mediated location of olive fly larvae by the braconid parasitoid Psyttalia concolor : A Multivariate comparison among VOC bouquets from three olive cultivars. Biomed Res Int ID 7827617. https://doi.org/10.1155/2016/7827615
Giunti G, Palmeri V, Algeri GM, Campolo O (2018) VOC emissions influence intra- and interspecific interactions among stored-product Coleoptera in paddy rice. Sci Rep 8:1–9. https://doi.org/10.1038/s41598-018-20420-2
Gouinguené S, Degen T, Turlings TCJ (2001) Variability in herbivore-induced odour emissions among maize cultivars and their wild ancestors (teosinte). Chemoecology 11:9–16. https://doi.org/10.1007/PL00001832
Gouinguené S, Alborn H, Turlings TCJ (2003) Induction of volatile emissions in maize by different larval instars of Spodoptera littoralis. J Chem Ecol 29:145–162. https://doi.org/10.1023/A:1021984715420
Groot A, Heijboer A, Visser J, Dicke M (2003) Oviposition preference of Lygocoris pabulinus (Het., Miridae) in relation to plants and conspecifics. J Appl Entomol 127:65–71
Guofa Z, Overholt WA, Mochiah MB (2001) Changes in the distribution of lepidopteran maize stemborers in Kenya from the 1950s to 1990s. Int J Trop Insect Sci 21:395–402
Honda K (1995) Chemical basis of differential oviposition by lepidopterous insects. Arch Insect Biochem Physiol 30:1–23. https://doi.org/10.1002/arch.940300102
Horgan F (2012) Effects of leaf damage on oviposition choice in an invasive paropsine beetle. J Appl Entomol 136:271–281. https://doi.org/10.1111/j.1439-0418.2011.01634.x
Jelen HH, Wlazly K, Wasowicz E, Kaminski E (1998) Solid-phase microextraction for the analysis of some alcohols and esters in beer: comparison with static headspace method. J Agric Food Chem 46:1469–1473. https://doi.org/10.1021/jf9707290
Kaplan I, Denno RF (2007) Interspecific interactions in phytophagous insects revisited: A quantitative assessment of competition theory. Ecol Lett 10:977–994. https://doi.org/10.1111/j.1461-0248.2007.01093.x
Kessler A, Baldwin IT (2001) Defensive Function of Herbivore-induced plant volatile emission in nature. Science 291:2141–2144. https://doi.org/10.1126/science.291.5511.2141
Kfir R, Overholt WA, Khan ZR, Polaszek A (2002) Biology and management of economically important lepidopteran cereal stem borers in Africa. Annu Rev Entomol 47:701–731. https://doi.org/10.1146/annurev.ento.47.091201.145254
Khan ZR, Pickett JA, van den Berg J, Wadhams LJ, Woodcock CM (2000) Exploiting chemical ecology and species diversity: stemborer and striga control formaize and sorghum in Africa. Pest Manag Sci 56:957–962. https://doi.org/10.1002/1526-4998(200011)56:11%3C957::AID-PS236%3E3.0.CO;2-T
Konstantopoulou MA, Krokos FD, Mazomenos BE (2004) Chemical composition of corn leaf essential oils and their role in the oviposition behavior of Sesamia nonagrioides females. J Chem Ecol 30:2243–2256. https://doi.org/10.1023/B:JOEC.0000048786.12136.40
Krüger W, Van Den Berg J, Van Hamburg H (2008) The relative abundance of maize stemborers and their parasitoids at the Tshiombo irrigation scheme in Venda, South Africa. S Afr J Plant Soil 25:144–151. https://doi.org/10.1080/02571862.2008.10639910
Kumar H (1986) Enhancement of oviposition by Chilo patellus (Swinhoe) (Lepidoptera: Pyralidae) on maize plants by laval infestation. Appl Entomol Zool 21:539–545
Le Ru BP, Ong’amo GO, Moyal P, Ngala L, Musyoka B, Abdullah Z, Cugala D, Defabachew B, Haile TA, Kauma Matama T, Lada VY, Negassi B, Pallangyo B, Ravolonandrianina J, Sidumo A, Omwega CO, Schulthess F, Calatayud P-A, Silvain J-F (2006) Diversity of lepidopteran stem borers on monocotyledonous plants in eastern Africa and the islands of Madagascar and Zanzibar revisited. Bull Entomol Res 96:555–563. https://doi.org/10.1079/BER2006457
Leppik E, Frérot B (2014) Maize field odorscape during the oviposition flight of the European corn borer. Chemoecology 24(6):221–228. https://doi.org/10.1007/s00049-014-0165-2
Lum PTM (1979) Degeneration of ova in the bulla seminalis of Lepidoptera. J Insect Physiol 25:595–599. https://doi.org/10.1016/0022-1910(79)90075-1
Maclellan CR (1962) Mortality of codling moth eggs and young larvae in an integrated control orchard. Can Entomol 94:655–666. https://doi.org/10.4039/Ent94655-6
Mattiacci L, Dicke M, Posthumust MA (1994) Induction of parasitoid atracting synomone in brussels-sprouts plants by feeding of Pieris brassicae larvae-role of mechanical damage and herbivore elicitors. J Chem Ecol 20:2229–2247. https://doi.org/10.1007/BF02033199
Memmott J, Gibson R, Carvalheiro LG, Henson K, Heleno RH, Mikel ML, Pearce S (2007) The conservation of ecological interactions. In: Stewart AJA, New TR, Lewis OT (eds) Insect conservation biology. CABI, Wallingford, pp 226–244. https://doi.org/10.1079/9781845932541.0226
Moolman J, Van den Berg J, Conlong D, Cugala D, Siebert S, Le Ru B (2014) Species diversity and distribution of lepidopteran stem borers in South Africa and Mozambique. J Appl Entomol 138:52–66
National Institutes of Standards and Technology (2008) NIST/EPA/NIH mass spectral library at http://www.nist.gov
Ngi-Song AJ, Overholt WA, Njagi PGN, Dicke M, Ayertey JN, Lwande W (1996) Volatile infochemicals used in host and host habitat location by Cotesia flavipes Cameron and Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae), larval parasitoids of stemborers on Graminae. J Chem Ecol 22:307–323. https://doi.org/10.1007/BF02055101
Ngi-Song AJ, Njagi PGN, Torto B, Overholt WA (2000) Identification of behaviourally active components from maize volatiles for the stemborer parasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae). Int J Trop Insect Sci 20:181–189. https://doi.org/10.1017/S1742758400019615
Ntiri ES (2015) Estimating the impacts of climate change on interactions between different lepidopteran stemborer species. PhD thesis. North-West University (Potchefstroom Campus)
Ntiri ES, Calatayud PA, Van Den Berg J, Schulthess F, Le Ru BP (2016) Influence of temperature on intra- And interspecific resource utilization within a community of lepidopteran maize stemborers. PLoS One 11:e148735. https://doi.org/10.1371/journal.pone.0148735
Ntiri ES, Calatayud PA, Musyoka B, Van Den Berg J, Le Ru BP (2018) Influence of feeding-damaged plants on oviposition responses within a community of female moths. Phytoparasitica. https://doi.org/10.1007/s12600-018-0695-1
Ochieng RS, Onyango FO, Bungu MDO (1985) Improvement of techniques for mass-culture of Chilo partellus (Swinhoe). Insect Sci its Appl 6:425–428. https://doi.org/10.1017/S1742758400004744
Ong’amo GO, Le Rü BP, Dupas S, Moyal P, Muchugu E, Calatayud PA, Silvain JF (2006a) The role of wild host plants in the abundance of lepidopteran stem borers along altitudinal gradient in Kenya. Ann la Société Entomol Fr 42:363–370. https://doi.org/10.1080/00379271.2006.10697468
Ong’amo GO, Le Rü BP, Dupas S, Moyal P, Calatayud PA, Silvain JF (2006b) Distribution, pest status and agro-climatic preferences of lepidopteran stemborers of maize in Kenya. Ann la Société Entomol Fr 42:171–177. https://doi.org/10.1080/00379271.2006.10700620
Onyango FO, Ochieng’-Odero JER (1994) Continuous rearing of the maize stem borer Busseola fusca on an artificial diet. Entomol Exp Appl 73:139–144. https://doi.org/10.1111/j.1570-7458.1994.tb01848.x
Pare PW, Tumlinson JH (1999) Plant volatiles as a defense against insect herbivores. Plant Physiol 121:325–331. https://doi.org/10.1104/pp.121.2.325
Peñaflor MFGV, Erb M, Robert CAM, Miranda LA, Werneburg AG, Dossi FCA, Turlings TCJ, Bento JMS (2011) Oviposition by a moth suppresses constitutive and herbivore-induced plant volatiles in maize. Planta 234:207–215. https://doi.org/10.1007/s00425-011-1409-9
Petit C, Ahuya P, Le Ru B, Kaiser-Arnauld L, Harry M, Calatayud P-A (2018) Influence of prolonged dietary experience during the larval stage on novel odour preferences in adults of noctuid stem borer moths (Lepidoptera: Noctuidae). Eur J Entomol 115:112–116. https://doi.org/10.14411/eje.2018.009
Pinto-Zevallos DM, Strapasson P, Zarbin PHG (2016) Herbivore-induced volatile organic compounds emitted by maize: Electrophysiological responses in Spodoptera frugiperda females. Phytochem Lett 16:70–74. https://doi.org/10.1016/j.phytol.2016.03.005
Poelman EH, Broekgaarden C, Van Loon JJA, Dicke M (2008) Early season herbivore differentially affects plant defence responses to subsequently colonizing herbivores and their abundance in the field. Mol Ecol 17:3352–3365. https://doi.org/10.1111/j.1365-294X.2008.03838.x
R Core Team (2017) R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing. https://www.R-project.org/
Roberts DD, Pollien P, Milo C (2000) Solid-phase microextraction method development for headspace analysis of volatile flavor compounds. J Agric Food Chem 48:2430–2437. https://doi.org/10.1021/jf991116l
Rothschild M, Schoonhoven LM (1977) Assessment of egg loard by Pieris brassicae (Lepidoptera: Pieridae). Nature 266:352–355. https://doi.org/10.1038/266352a0
Sato Y, Yano S, Takabayashi J, Ohsaki N (1999) Pieris rapae (Lepidoptera: Pieridae) females avoid oviposition on Rorippa indica plants infested by conspecific larvae. Appl Entomol Zool 34:333–337. https://doi.org/10.1303/aez.34.333
Shiojiri K, Takabayashi J, Yano S, Takafuji A (2002) Oviposition preferences of herbivores are affected by tritrophic interaction webs. Ecol Lett 5:186–192. https://doi.org/10.1046/j.1461-0248.2002.00292.x
Skoczek A, Piesik D, Wenda-Piesik A, Buszewski B, Bocianowski J, Wawrzyniak M (2017) Volatile organic compounds released by maize following herbivory or insect extract application and communication between plants. J Appl Entomol 141:630–643. https://doi.org/10.1111/jen.12367
Speight MR, Hunter MD, Watt AD (2008) Ecology of insects: concepts and applications, 2nd edn. Environ Entomol Entomol Soc Am. https://doi.org/10.1603/022.038.0448
Steidle JLM, Fischer A, Gantert C (2005) Do grains whisper for help? Evidence for herbivore-induced synomones in wheat grains. Entomol Exp Appl 115:239–245. https://doi.org/10.1111/j.1570-7458.2005.00295.x
Takabayashi J, Dicke M, Posthumus MA (1994) Volatile herbivore-induced terpenoids in plant-mite interactions: variation caused by biotic and abiotic factors. J Chem Ecol 20:1329–1354. https://doi.org/10.1007/BF02059811
Trematerra P, Valente A, Athanassiou CG, Kavallieratos NG (2007) Kernel–kernel interactions and behavioral responses of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Appl Entomol Zool 42:129–135. https://doi.org/10.1303/aez.2007.129
Ukeh DA, Woodcock CM, Pickett JA, Birkett MA (2012) Identification of Host Kairomones from Maize, Zea mays, for the Maize Weevil, Sitophilus zeamais. J Chem Ecol 38:1402–1409. https://doi.org/10.1007/s10886-012-0191-x
Underwood DLA (1994) Methods for sexing Lepidoptera larvae. J Lepid Soc 48(3):258–263
Van Rensburg JBJ, Van den Berg J (1992) Infestation patterns of the stalk borers Busseola fusca Fuller (Lep.: Noctuidae) and Chilo partellus Swinhoe (Lep.: Pyralidae) in grain sorghum. J Entomol Soc S Afr 55:197–212
Viswanathan DV, Narwani AJ, Thaler JS (2005) Specificity in induced plant responses shapes patterns of herbivore occurrence on Solanum dulcamara. Ecology 86:886–896. https://doi.org/10.1890/04-0313
Viswanathan DV, Narwani AJT, Thaler JS (2015) Specificity in induced plant responses shapes patterns of herbivore occurrence of Solanum dulcamara. Ecology 86:886–896. https://doi.org/10.2307/3450842
Wise JM, Weinberg MA (2002) Prior flea beetle herbivory affects oviposition preference and larval performance of a potato beetle on their shared host plant. Ecol Entomol 27:115–122. https://doi.org/10.1046/j.0307-6946.2001.00383.x
Wootton JT, Emmerson M (2005) Measurement of interaction strength in nature. Annu Rev Ecol Evol Syst 36:419–444. https://doi.org/10.1146/annurev.ecolsys.36.091704.175535
Acknowledgements
The authors wish to thank IRD for funding the research; the German Academic Exchange Service (DAAD) for funding the PhD fellowship under the grant number 91636630, University of Nairobi and icipe capacity building Capacity Building Program (ARPPIS) for hosting the PhD student. Thanks are also given to the staff of the IRD-NSBB project and BCED Unit at icipe, especially Boaz Musyoka and Onesmus Kaye Wanyama for their technical assistance provided. They also thank the stemborer rearing unit of the ARCU-icipe, especially Peter Malusi for the rearing and supply of insect larvae for this experiment. Thanks also to Fritz Schulthess for his critical review of the manuscript.
Author information
Authors and Affiliations
Corresponding author
Electronic supplementary material
Below is the link to the electronic supplementary material.
Rights and permissions
About this article
Cite this article
Sokame, B.M., Ntiri, E.S., Ahuya, P. et al. Caterpillar-induced plant volatiles attract conspecific and heterospecific adults for oviposition within a community of lepidopteran stemborers on maize plant. Chemoecology 29, 89–101 (2019). https://doi.org/10.1007/s00049-019-00279-z
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00049-019-00279-z