Introduction

Mung bean is one of the most important legume crops in many Asian countries, including Korea (Hong et al. 2015; Malik 1994; Somta et al. 2008). At least three species of bruchines are known to attack mung bean (Talekar 1988). Among the bruchines, azuki bean weevil, Callosobruchus chinensis (L.) is a pest of Vigna beans such as mung bean (V. radiata) and cowpeas (V. unguiculata) (Tuda et al. 2005). It is a widely distributed species throughout the tropical and sub-tropical regions of the world (Rees 2004; Southgate 1979). Infestation by C. chinensis starts in the field and can cause severe damage to stored leguminous seeds (Bellows 1982; Southgate 1984). Damage to stored mung bean seeds leads to weight loss, low viability of seeds, and low nutritional quality (de Sa et al. 2014; Talekar 1988). Losses of 35% in Central America (McGuire and Cradall 1967), 7–13% in South America (Schoonhoven 1976), and 73% in Africa have been recorded for this pest (Khamala 1978; Nahdy 1994). Immature stages, especially larva, of the beetle spend their entire time inside the seeds (Credland and Wright 1990), and reduce nutritional value of seeds (Tohiuddin et al. 1993).

Callosobruchus maculatus (F.) beetles commonly mate and oviposit immediately after adult emergence and spend adulthood without water and food (Chiu and Messina 1994). Adults of C. chinensis lay numerous eggs on seeds and can complete many overlapping generations (6–7) during seed storage (Chandra 2006). Callosobruchus chinensis have a wide range of leguminous hosts on which they successfully develop (Fujii 1968; Nakamura 1969). Host selection for oviposition by adult C. chinensis has important fitness consequences, because offspring survival is influenced by physical and biochemical factors of seed coats (Nwanze et al. 1975), seed size (Horber 1983), thickness of seed coat (Gupta and Mishra 1970), geographical differences among host plants (Horton et al. 1988; Scriber 1986), host quality (Bernays and Chapman 1994; Coyle et al. 2011; Heisswolf et al. 2005; Hoffman and Rao 2011; Mangel 1989), and plant chemical defense compounds (Dobie 1981; Janzen et al. 1976) as well as abiotic factors such as temperature (Howe and Currie 1964; Maharjan et al. 2017). Female seed beetles have the ability to discriminate quality of host seeds, and do distribute their eggs according to host seed size in a manner that maximizes the amount of resources and secures the offspring survival (Cope and Fox 2003). Prior experience with particular hosts can also alter beetle orientation and host acceptance for oviposition (Howard and Bernays 1991; Papaj and Prokopy 1989; Szentesi and Jermy 1990). Natural selection shapes the oviposition behavior of bruchine seed beetles so as to maximize individual fitness because immature life stages of beetles have limited mobility and beetle larvae must feed on the seed on which oviposition occurred (Cope and Fox 2003; Wijeratne 1998).

Callosobruchus chinensis has until recently been managed with chemical pesticides and fumigants, but insecticide residues can remain on treated seeds, reducing their quality for both human consumption and planting. Other effective, low-cost control methods have therefore been sought, such as plants with natural resistance to bruchine beetles. Several studies have reported resistance of the wild mung bean [V. radiata var. sublobata (Roxb.) Verdc.], to bruchines, whose use in plant breeding programs has led to a number of newly developed mung bean cultivars (TC1966, V2709 and V2802, ACC23, and ACC41) (Fujii and Miyazaki 1987; Fujii et al. 1989; Lambrides and Imrie 2000; Talekar and Lin 1992). In Korea, three mung bean cultivars are widely grown: cv. Seonhwa, cv. Gyeongseon, and cv. Jangan. Among these, cv. Jangan is reported to be particularly resistant to bruchines and stink bugs, a trait developed by back crossing with the V2709 resistant donor (Bae et al. 2009; Hong et al. 2015). Previous studies have reported cowpea seeds to be the most preferred host for C. chinensis oviposition (Mainali et al. 2015a, b). However, information on the oviposition behavior and development of bruchines on these cultivars is limited and is needed to help breeders enhance the development of resistant lines for use in Korea. In this study, we evaluated the oviposition preference and development of the C. chinensis on three mung bean varieties Seonhwa, Gyeongseon, and Jangan, and compared this to cowpea, cv. Yeonbun. Studies have reported temperature is a critical factor, and it has been an important source of variation in bruchine development and oviposition choices (Maharjan et al. 2017; Mainali et al. 2015a, b); therefore, our experiments were also conducted in four constant temperatures.

Materials and methods

Insect rearing

Azuki bean weevil adults were collected from a field of azuki bean, Vigna angularis (Willd.) Ohwi & Ohashi, of NICS, RDA in Miryang (Gyeongsangnam-do; 35° 49′ N, 128° 74′ E), Korea in 2011. This field-collected population was maintained in the laboratory on azuki bean seeds, cv. Hongeon, for over a year before being used in this study. Collected adult weevils were held in a square shaped, transparent petri-plate (24 length × 2.5 height cm with lid ventilation) and provided with azuki bean seeds. All petri-plates were held at 28 ± 1 °C, 50 ± 5% RH and a 16:8 h L:D photoperiod. Adults were collected with the help of a glass funnel.

Azuki bean weevil adults used in this study were collected from a location where average high temperature and relative humidity during the azuki bean cultivation season are around 31 °C and 72%, respectively. However, average daily temperature for each month during cultivation season ranged from 18.5 to 28.9 °C. The experimental conditions we chose were, therefore, similar to the average of the environmental conditions that the adult weevils would experience in the field. We thus believe this minimizes the possible variations in results due to the environmental conditions experienced by C. chinensis.

Sources of seeds

One bruchine -resistant mung bean cultivar [cv. Jangan: Geumseong Nokdu (Korean cultivar) × AVI-3-1 (AVRDC pedigree)], two susceptible cultivars [cv. Seonhwa (AVRDC line) and cv. Gyeongseon: Gyeonggi Nokdu (Korean cultivar) × VC3738A (AVRDC pedigree)], and cowpea [cv. Yeonbun (pure line selection from Yecheon landrace, Korea)] were used in this study. Mung bean and cowpea seeds were dried to a consistent moisture level (< 12%) before being tested. To determine the seed size of each legume species, digital photographs of seeds were taken with a Nikon D300 digital SLR camera. The camera was fixed pointing down on the frame at a height of 40 cm. The length of seeds was measured from looking at these photographs on a Leica M205C stereomicroscope (Leica, Wetzlar, Germany), and the net length of seeds of each legume species was analyzed. Previous studies reported that an image analysis system has been widely adopted and used to measure the size and shape, and even physical properties of a wide range of crop seeds and fruits (Boydas et al. 2012; Ercisli et al. 2012; Firatligil-Durmus et al. 2010; Kara et al. 2013; Sayinci et al. 2012; Venora et al. 2007; Yurtlu and Yesiloglu 2011). However, moisture content, variation in carbon, and the carbon/nitrogen relation can also influence seed hardness and seed size (Amin et al. 2004; Kanawde et al. 1990; McGinley and Charnov 1988). A total of 100 seeds were measured for each species.

No-choice and choice experiments

Observations on the oviposition preference, developmental time, adult emergence, and adult weight of C. chinensis on different mung bean and cowpea seeds were carried out at 28 ± 1 °C, 50 ± 5% RH and a 16:8 h L:D photoperiod. Twenty seeds of mung bean (cvs. Seonhwa and Gyeongseon [susceptible], Jangan [resistant], or cowpea (cv. Yeonbun) were placed in a petri-dish (5 cm dia. × 1.5 cm height), and held inside a fine mesh ventilated breeding dish (14.5 cm dia. × 2.5 cm height) for a no-choice experiment in which a pair of newly emerged adult C. chinensis was introduced to the legumes.

In a separate choice experiment, another newly emerged pair of C. chinensis was introduced to the legumes, with each legume (n = 20) presented separately in petri-dishes (5 cm dia. × 1.5 cm height), which themselves were placed together inside a fine mesh ventilated breeding dish (14.5 cm dia. × 2.5 cm height) with random distribution.

In both experiments, the introduced weevils were allowed to lay eggs for 72 h. After every 24 h, seeds with eggs were removed and replaced with new seeds, and the numbers of eggs per seed were counted. The seeds with eggs were held under the same conditions until adult emergence. Two days after adult emergence, unmated adults were counted and weighed with a digital scale (Sartorius, CP124S, Sartorius AG Gottingen, Germany). Their sex was then determined, and weevils were placed individually in micro-tubes (1.3 cm dia., 3.8 cm height, vol. 1.7 ml; Scientific Specialties Inc. USA) without water or food to determine the longevity of each male and female. A week after adult emergence, seeds were also dissected to determine immature mortality. After death, adults were sexed based on the morphology of antenna (Hu et al. 2009). Each experiment was replicated 15 times.

Temperature experiment

Developmental time, adult longevity, and sex ratio of C. chinensis was examined at four constant temperatures [20, 25, 30, and 35 °C (± 0.5 °C)], 75 ± 5% RH, and a 16:8 h L:D photoperiod. The RH level within the chambers was maintained by using saturated salt solutions (Duksan Pure Chemicals, Korea) as described in Winston and Bates (1960). The saturated salt solution used was NaCl to maintain 75% RH. To monitor these conditions (temperature and humidity), data loggers [Huato Log-USB, Huato Electronic (Shenzhen) Co. Ltd., China] were used to record the actual temperature inside the environmental chambers. To allow oviposition, seeds of each legume (100 seeds/legume variety) were exposed for 24 h to a laboratory colony C. chinensis (a mixed sex population, 1–2 days old) in a square, transparent petri-plate (25 cm L × 15.5 cm W × 15 cm H) at 28 ± 1 °C, 50 ± 5% RH and a 16: 8 h L: D photoperiod. Since oviposition could only take place during this period, the age of the eggs and therefore of the subsequent larvae were uniform. After this 24 -h exposure, adult C. chinensis were removed, and eggs were tracked and counted using a stereomicroscope (4.4:1, 35X, Leica EZ4, Wetzlar, Germany). Any seeds bearing eggs were placed individually into a centrifuge-tube case (13.5 cm L × 13.5 cm W × 5 cm H with 100 individual wells; Daihan Scientific, Korea), and held inside humidity chambers (27 cm L × 20 cm W × 17 cm H). Humidity chambers were then placed inside incubators (Eyela, model-MTI-202B, Japan) set at 20, 25, 30, and 35 °C. The larva and pupa stages of C. chinensis were separated according to Campbell et al. (1976). To measure the duration of each developmental stage, some seeds were dissected every 12 h to identify the developmental stage, and observations were made until adult emergence or death of all insects in the experiment. Once adults emerged, their sex was determined, and they were kept individually in micro-tubes (1.3 cm dia., 3.8 cm height, vol. 1.7 ml; Scientific Specialties Inc. USA) without food or water until death to determine the adult longevity providing respective temperatures used during their development.

Seed weight loss

Seed weight was measured with a digital balance (Sartorius, CP124S, Sartorius AG Gottingen, Germany) before and after use in the study. Weight loss of seeds was estimated by subtracting weight of seeds after being exposed to C. chinensis from the initial weight.

Statistical analysis

Seed size and number of eggs laid, for both no-choice and choice tests, were analyzed using one-way analysis of variance (ANOVA), PROC GLM in SAS (SAS Institute Inc 2000), and Tukey’s test was used for post hoc analysis. Developmental time and adult longevity were analyzed using a two-way ANOVA, and the Tukey’s test was used for post hoc analysis for sex, varieties, and their interactions (SAS Institute Inc 2000). Adult emergence rates were analyzed with a Chi-square test using a contingency table and a post hoc multiple comparison test analogous to the Tukey’s test (Zar 2010). Developmental time of life stages on different leguminous seeds at different temperatures were analyzed using one-way analysis of variance (ANOVA), PROC GLM in SAS (SAS Institute Inc 2000) and the Tukey’s test was used for post hoc analysis. Longevity was compared between females and males with t-tests.

Results

Seed size

The leguminous seeds from different species or varieties used in the study were significantly different in size (F = 2094.34, df = 3, 396, p < 0.0001). Among the cultivars, the mung bean seed, cv. Jangan was the smallest in size.

No-choice and choice experiments

Oviposition

The ovipositional response of female C. chinensis varied with different leguminous seed sources. The number of eggs laid was significantly higher on the cowpea seeds (cv. Yeonbun) in both no-choice (F = 529.27, df = 3, 76, p < 0.0001) and choice tests (F = 1230.9, df = 3, 76, p < 0.0001), followed by mung bean, cvs. Seonhwa and Gyeongseon (Fig. 1). Mung bean cv. Jangan had the fewest eggs in both tests (no-choice: 0.7 per seed and choice: 0.4 per seed).

Fig. 1
figure 1

Number of eggs (mean ± SE) laid by a Callosobruchus chinensis female on different legume seeds in no-choice and choice tests in a period of 72 h. All paired means differed significantly (p < 0.05)

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Developmental time

The developmental time [egg- adult (oviposition date to adult emergence)] of C. chinensis also varied significantly on legume seeds of different species of varieties tested in both no-choice (F = 407.15, df = 7, 110, p < 0.0001), and choice tests (F = 266.48, df = 7, 56, p < 0.0001). The developmental time was found to be significantly shorter on cowpea, cv. Yeonbun in both no-choice (F = 635.91, df = 3, 110, p < 0.0001), and choice (F = 441.77, df = 3, 56, p < 0.0001) tests compared to values on mung bean cultivars. The longest developmental time was found on mung bean, cv. Jangan (Fig. 2). A significant difference in developmental time between weevil sexes was found in both no-choice (F = 933.03, df = 1, 110, p < 0.0001), and choice (F = 489.86, df = 1, 56, p < 0.0001) tests. Also, significant differences in the interaction between seed types (species or varieties) and sexes were detected in both no-choice (F = 3.11, df = 3, 110, p = 0.02), and choice (F = 16.72, df = 3, 56, p < 0.0001) tests (Fig. 2).

Fig. 2
figure 2

Developmental time (day, mean ± SE) of Callosobruchus chinensis on different legume seeds in no-choice and choice tests. Capital and small letters above bars denote differences among cultivars for female and male, respectively (Tukey’s test, p < 0.05). Asterisk denotes the significant differences between sexes (t test, p < 0.05)

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Adult emergence

We found significant differences in the number of adult emergences among legume seeds types (species or varieties). Higher adult emergence was recorded on the cowpea, cv. Yeonbun in the no-choice (χ 2 = 13.73, df = 3, p = 0.003), while adult emergence rates were not different between mung bean cvs. Seonhwa and Gyeongseon. Higher adult emergence rates were recorded on cowpea, cv. Yeonbun and mung bean, cv. Seonhwa than mung bean cv. Jangan in the choice (χ 2 = 12.36, df = 3, p = 0.006) tests (Fig. 3).

Fig. 3
figure 3

Adult emergence rates of Callosobruchus chinensis from different legume seeds in no-choice and choice tests. Bars represent standard error. Means followed by same letters are not significantly different (p < 0.05)

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Adult longevity

Adult longevity of C. chinensis under conditions of starvation and lack of water was found to differ among leguminous seeds in both no-choice (F = 111.36, df = 7, 109, p < 0.0001), and choice (F = 73.32, df = 7, 96, p < 0.0001) tests. Adults that emerged from cowpea seeds, cv. Yeonbun were found to be longer-lived than those emerging from mung bean cultivars, while the shortest longevity was found on the mung bean, cv. Jangan in both no-choice (F = 200.55, df = 3, 109, p < 0.0001), and choice (F = 111.00, df = 3, 96, p < 0.0001) tests. A significant difference in longevity between sexes was detected in both no-choice (F = 165.24, df = 1, 109, p < 0.0001), and choice (F = 160.69, df = 1, 96, p < 0.0001) tests. Also, significant differences in the interaction between seed type and beetles sex were detected in both no-choice (F = 4.20, df = 3, 109, p = 0.007), and choice (F = 6.53, df = 3, 96, p = 0.0005) tests (Fig. 4).

Fig. 4
figure 4

Adult longevity (day, mean ± SE) of female and male Callosobruchus chinensis that emerged from different legume seeds from no-choice and choice tests. Capital and small letters above bars denote differences among cultivars for female and male, respectively (Tukey’s test, p < 0.05). Asterisk denotes the significant differences between sexes (t test, p < 0.05)

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Adult weight

Adults of C. chinensis that emerged from the mung bean, cv. Seonhwa were significantly heavier than adults from other seed types, in both no-choice (F = 42.57, df = 3, 252, p < 0.0001) and choice (F = 17.00, df = 3, 217, p < 0.0001) tests (Fig. 5).

Fig. 5
figure 5

Adult weight (mg, mean ± SE) of Callosobruchus chinensis that emerged from different legume seeds in no-choice and choice tests. Means followed by same letters are not significantly different (p < 0.05)

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Temperature experiment

Developmental time

The developmental time (oviposition date to adult emergence) of C. chinensis varied significantly with temperatures on different legume seed types: 20 °C (F = 88.92, df = 2, 93, p < 0.0001), 25 °C (F = 2.71, df = 2, 227, p = 0.04). 30 °C (F = 11.20, df = 2, 163, p < 0.0001), and 35 °C (F = 8.13, df = 2125, p = 0.0005) (Table 1). Developmental time was significantly shorter on cowpea, cv. Yeonbun at all tested temperatures. Meanwhile, larva could not survive on the mung bean, cv. Jangan at any temperature.

Table 1 Developmental time (day, mean ± SE) of immature stages, adult females and males, and sex ratio of Callosobruchus chinensis on different species or varieties of legume seeds at constant temperatures
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Adult longevity

Adult longevity of C. chinensis under conditions of starvation and lack of water, was found to differ with temperature among legume seed types: 20 °C (female: F = 7.66, df = 2, 118, p = 0.0007 and male: F = 4.32, df = 2, 104, p = 0.01), 25 °C (female: F = 5.33, df = 2, 125, p = 0.006 and male: F = 3.98, df = 2, 98, p = 0.02), and 30 °C (female: F = 4.32, df = 2, 78, p = 0.01 and male: F = 2.94, df = 2, 82, p = 0.05). Adults that emerged from the cowpea seeds, cv. Yeonbun, lived longer than those that emerged from the mung bean cultivars at 20, 25 and 30 °C, and females lived longer than males at 20 °C (cowpea, cv. Yeonbun: t = 2.01, p = 0.04), 25 °C (cowpea, cv. Yeonbun: t = 3.43, p = 0.001, mung bean, cvs. Seonhwa: t = 6.63, p < 0.0001 and Gyeongseon: t = 2.53, p = 0.01), and 30 °C (cowpea, cv. Yeonbun: t = 2.79, p = 0.007, mung bean, cv. Seonhwa: t = 3.79, p = 0.0004), and 35 °C (mung bean, cvs. Seonhwa: t = 2.23, p = 0.02 and Gyeongseon: t = 2.32, p = 0.02) (Table 2).

Table 2 Adult longevity (day, mean ± SE) of female and male Callosobruchus chinensis that emerged from different legume seeds held at constant temperatures
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Sex ratio

Callosobruchus chinensis sex ratio (proportion of female) was not different among legume cultivars (p > 0.05) (Table 1). The female proportion of individuals reaching adulthood was almost a 1:1 ratio.

Seed weight loss

Seed weight loss was found to differ with temperature among legume seed types: 20 °C (F = 61.44, df = 3, 284, p < 0.0001), 25 °C (F = 30.64, df = 3, 348, p < 0.0001), and 30 °C (F = 19.74, df = 3, 348, p < 0.0001), and 35 °C (F = 43.65, df = 3, 348, p < 0.0001) (Table 3). The least seed weight loss was recorded for mung bean, cv. Jangan.

Table 3 Seed weight loss (mg, mean ± SE) of legume seeds after Callosobruchus chinensis consumption at constant temperatures
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Discussion

In this study, Callosobruchus chinensis showed a consistent oviposition preference to one legume varieties among the tested legume varieties. Previous studies have suggested that beetles varieties preference could be related to physical characteristics of seed such as seed size, surface area of seed, seed texture and so on (Cope and Fox 2003; de Sa et al. 2014; Huignard et al. 1985; Mitchell 1990). Instead, females must either use olfactory cues other than physical parameters of seeds for host location and continued through oviposition (Cope and Fox 2003). Credland and Wright (1988) reported that chemical cues from the seeds play a vital role in oviposition, and C. maculatus discriminate among hosts based on odors, which response is further mediated by taste receptors on the maxillary palps (Messina et al. 1987), demonstrating that olfaction is used by beetles in host location. Moreover, chemical compounds such as phenol concentration in seed (Bhattacharya and Banerjee 2001), and seed morphology and texture can also influence the oviposition choice of female Callosobruchus spp. (Brewer and Horber 1983; de Sa et al. 2014; Huignard et al. 1985; Janzen 1977; Nwanze and Horber 1976).

In this study, we found a higher number of eggs laid by C. chinensis on cowpea, cv. Yeonbun in both no-choice and choice tests. This might be due to the size of seeds. The seeds of cowpea had a larger surface than the mung bean seeds, findings that are in line with that of Seddiqi (1972), and Bhattacharya and Banerjee (2001), who reported more eggs were laid by Callosobruchus spp. on larger seeds. Very few eggs were laid by C. chinensis on mung bean, cv. Jangan in either no-choice or choice tests. This low preference on mung bean, cv. Jangan might be associated with its rough seed coat and small size. Previous studies have shown that both C. chinensis and C. maculatus choose leguminous seeds with smooth seed coat for oviposition (Bhattacharya and Banerjee 2001; de Sa et al. 2014; Girish et al. 1974; Huignard et al. 1985; Nwanze et al. 1975; Southgate 1979). Further, a small seed size functions as a protection mechanism against bruchines through countermechanisms to defensive traits against bruchines such as gum production by pods, dehiscence, smaller size of seeds, indehiscence, and flaking of pod surface (Center and Johnson 1974).

In this study, we noticed scraped markings (2–3 short lines) made by C. chinensis on the seeds with rough seed coat such as mung bean, cv. Jangan (personal observation), suggesting the beetles prefer suitable seed hosts on which their offspring will have the best chance to survive and develop. Study has shown that both larvae and adults of C. maculatus altered their host preference behavior based on past experience (Wasserman 1981). In addition, the test insect used in this study (C. chinensis) was originally collected from an azuki bean field and reared on the azuki bean seed for successive generations, precisely so that host preferences would not be influenced by previous feeding experience. The results presented here suggest that C. chinensis can complete its development on cowpea, cv. Yeonbun, and mung bean, cvs. Seonhwa and Gyeongseon, but not on mung bean, cv. Jangan. This phenomenon, similar to the ovipositional preference of C. chinensis, might be mediated by nutrient and the morphology/physical characteristics and chemicals associated with the seeds (Brewer and Horber 1983; Janzen 1977; Panizzi 1987). In this study, none of C. chinensis were able to develop on mung bean, cv. Jangan in constant temperature experiments. Microscopic observation showed that internal damage occurred by larvae from mung bean cv. Jangan and all larva of C. chinensis feeding on the cv. Jangan died in the first and second instar due to a failure to penetrate through the seed coat to the cotyledons. Similarly, Somta et al. (2008) reported that first and second instar larvae failed to develop because of plant defense compounds in the embryo and/or cotyledons and that such insecticidal chemicals play a vital role in making a seed coat resistant to bruchines. Several studies related to biochemical defense in legume seeds (see Kashiwaba et al. 2003; Somta et al. 2006; Sugawara et al. 1996; Talekar and Lin 1992 for examples) have been reviewed by Gatehouse et al. (1990). Seed genotypes can also influence resistance characteristics against bruchines (Kitamura et al. 1988).

In this study, we found the shortest developmental time of C. chinensis was on cowpea seeds, in both no-choice and choice tests, and in the constant temperature experiments. These findings are in line with that of Mainali et al. 2015a, b, who reported the shortest developmental time on cowpea seeds, and stand in contrast to the result of Kim and Choi (1987) who reported that the shortest developmental time was on the azuki bean seed. In our study, females took longer to develop than males. Tuda and Shimada (1995) also reported longer female development. The results from our constant temperature experiments also suggests that ovipositional behavior and development of C. chinensis are influenced first by host seeds but then by environmental conditions.

Higher adult emergence was recorded from mung bean, cv. Seonhwa and cowpea, cv. Yeonbun in choice tests. Similarly, adults that emerged from the cowpea, cv. Yeonbun lived longer in both no-choice and choice tests, and in the constant temperature experiments; meanwhile, males lived for shorter periods than females, similar to findings by Seddiqi (1972) and Mainali et al. 2015a, b, who reported higher adult emergence from mung bean and cowpea seeds, and contrary to the findings of Tuda and Shimada (1995), who found no difference in longevity of males and females. This discrepancy might be due to differences in the genetic makeup of each insect population. Adults of C. chinensis that emerged from the mung bean, cv. Jangan were weighed significantly less than adults that emerged from other seed types tested here. This difference might be due to a longer exposure to the defensive biochemicals and proteins associated with seeds such as cyclopeptide alkaloid (Sugawara et al. 1996), trypsin (Dobie 1981), peptide compound ‘GIF-5′ (Kaga et al. 2000), and cysteine-rich protein (Chan et al. 2005; Chen et al. 2002).

The ovipositional behavior preference and developmental time trend of C. chinensis in both no-choice and choice tests, and in the constant temperature experiments were similar. From both experiments, mung bean, cv. Jangan is found to be the least attractive seed host for oviposition, development, adult emergence, and shortest adult longevity. It also had the lowest seed weight losses. The behavioral preference of C. chinensis and its performance on different seeds is likely mediated by the biochemicals and toxicity associated with the seeds as discussed earlier. Our findings suggest that mung bean cv. Jangan could be a model seed source for exploring resistance related to seed chemicals to better understand resistance mechanisms against bruchines. Further, this information could be a base to enhance the resistant breeding program of mung beans in Korea.