INTRODUCTION Pulses are indeed an important source of dietary fibre and high-quality protein. They play a vital role in food and nutritional security, with a lot of potential in meeting future global food security, nutrition, and environmental sustainability needs (Singh et al., 2016). In India, pulses have been cultivated over an area of 28.8 million hectares, with total production of 25.72 million metric tons, yielding about 892 Kg/ha annually (Anonymous, 2022), and thus being the world’s largest producer, consumer and importer of pulses (Vishwakarma et al., 2019). Nevertheless, there are some constraints exists in the production as well as the post-production of pulses. Being highly proteinaceous, pulses are more prone to storage pests and that alone accounts for 5-10 % losses in pulses (Lal and Verma 2007). Pulse beetle, Callosobruchus spp. (Chrysomelidae: Coleoptera), also called bruchids, are quite well regarded as the most devastating pulse storage pest, particularly in the tropics and subtropics, causing notable losses to the stored pulse commodities (Mishra et al., 2017). The extent of damage and lossincurred by bruchids is variable depending on the crop and species. Among the species, Callosobruchus maculatus (Fabricius) and C. chinensis (Linnaeus) are the most notorious infesting several pulses such as cowpea, mung bean, black gram, chickpea, horse gram etc., during storage. In recent times, the bruchid species C. phaseoli has known to infest stored lablab seeds. During the recent survey, occurrence of Callosobruchus phaseoli (Gyllenhal) was recorded in stored lablab seeds and until now this species has not been reported from Tamil Nadu. C. phaseoli measures about 2.7 – 3.5 mm length and 1.5 – 1.7 mm width, having golden yellow brown body colouration. Like any other bruchid, it also glues its egg to the seed surface, the emerging grub entirely damages the cotyledon, and the adults make their way out by making circular exit holes. In view of C. phaseoli may expand its host range in future, the present study was focussed on identifying the host preference of bruchid by studying its biology in various pulses and to determine the range of susceptibility in pulses genotypes. MATERIALS AND METHODS Experiment details. The study was conducted at the Department of Agricultural Entomology, Tamil Nadu Agricultural University (TNAU), Coimbatore, Tamil Nadu from November 2021 to May 2022 by utilising Completely Randomized Design with three replications. Seed materials. Different types of uninfested pulses viz., green peas (Pisum sativum), chickpea (Cicer arietinum) (Desi and kabuli type), kidney beans (Phaseolus vulgaris) (Speckled and brown), blackgram (Vigna mungo), greengram (Vigna radiata), cowpea (Vigna unguiculata) and horsegram (Macrotyloma uniflorum) were used for the host preference study and were procured from the local markets. Black kidney beans, a local landrace collected from Kolli hills, Tamil Nadu and dolichos bean (Lablab purpureus) (Variety CO(GB)14), obtained from the Department of Vegetable Sciences, TNAU, Coimbatore, were also included in this study. All the seed materials were pre-conditioned in the deep freezer at -23˚C for two weeks to eliminate the hidden infestation by any other storage pests and then the seeds were thawed at room temperature for five days before experimentation. Bruchid culture. Callosobruchus phaseoli adults used in this experiment were obtained from the pure culture maintained at Seed Health Laboratory, Directorate of Seed Centre, TNAU, Coimbatore. The male and female beetles were differentiated using the key characters (Kingsolver, 2004). Ten pairs of freshly emerged adults were released in uninfested white lablab seeds (100 g) kept in a plastic container (10 cm diameter, 20 cm height). Seeds were exposed for oviposition for two days and adults were removed. Freshly emerged adults from the culture were used for the experiments. The culture was retained throughout the study by periodical sub-culturing. ‘No-choice’ study. The host preference of C. phaseoli to different pulses was determined using no-choice method of screening (Aidbhavi et al., 2021). The number of seeds taken for study varied according to their size viz., kidney beans - 20 nos.; green peas, chickpea, lablab, kolli hills bean - 30 nos. each); cowpea - 40 nos. and greengram, blackgram, horsegram - 50 nos. each. The pre weighed seeds were taken in plastic vials (7.5 cm height, 5 cm diameter) three pairs of mated beetles were released in each vial and allowed to oviposit for four days. The biological parameters viz., oviposition (no. of eggs laid per ten seeds), egg hatching success (Giga and Smith 1987), adult emergence (%) and Mean Developmental Period (MDP) were observed. Finally, seed damage (%) and weight loss (%) were computed (Seram et al., 2016). Based on the above parameters, Susceptibilty Index (SI) (Howe, 1971) was calculated, and pulses seeds were categorized into immune (0.000), resistant (0.001-0.050), moderately resistant (0.051-0.055), moderately susceptible (0.056-0.060), susceptible (0.060-0.065) and highly susceptible (>0.065). Seed biophysical characteristics. The qualitative (Seed colour, lustre and texture) and quantitative (Seed dimensions, surface area and sphericity) parameters of different pulses were analysed to understand whether it has any relationship with the host susceptibility to C. phaseoli. The qualitative aspects like seed colour and lustre were visually observed. Seed texture was analysed under LEICA stereo zoom microscope (Model: S8APO). Seed length, breadth, width and seed coat thickness were measured using digital vernier calliper (Model: Kency). From the above parameters, seed surface area and seed sphericity were worked out as per Sewsaran et al. (2019). Statistical analysis. The data were statistically analysed by one way ANOVA using SPSS software version 22.0 and the means were compared by Duncan’s Multiple Range test (DMRT) at 5.0 % significance level. To stabilize the variance, data in percentage were transformed using arc-sine transformation, while others were transformed by square root transformation. To understand the mechanism of resistance, seed biophysical parameters were correlated with the biological parameters of C. phaseoli. RESULTS AND DISCUSSION A. Screening by no-choice test Biological parameters of C. Phaseoli obtained from the host preference study were given in Table 1. Eggs of C. phaseoli were observed on all the pulses seeds but there was significant variation in the rate of ovipositon. Maximum oviposition was observed in kidney beans (speckled) (70.17 eggs/10 seeds) and minimum in horsegram seeds (2.60 eggs/10seeds). Maximum eggs on kidney beans (speckled) might be due to the larger size, because seed size influence the ovipositon pattern of bruchid (Lambrides and Imrie 2000). The hatching success of bruchid eggs had a significant variation between the pulses. Hatched eggs were differentiated from the unhatched ones by their dirty white opaque colour (Unhatched eggs are shiny and translucent). Maximum percentage of egg hatching was noticed in chickpea (Desi type) (94.72%) and in green peas (94.43%), whereas only 33.70% eggs were hatched in kidney beans (Brown). Maximum adult emergence (%) was observed in lablab seeds (78.11%). In blackgram, black beans (local land race) and kidney beans (speckled and brown) no adult emergence was observed. Despite higher percentage of hatching success, the seeds of blackgram, black beans and kidney bean has not supported the larval development. This might be due to the presence of antinutritional factors in the seed cotyledon that has hindered the larval development. Under laboratory condition in lablab seeds, C. phaseoli adult emergence occurs in 25-28 days after oviposition. However, in this study, Mean Developmental Period (MDP) of C. phaseoli varied significantly in different pulses. MDP ranged from 0.0 to 32.78 days, with green peas registering the longest MDP. C. chinensis had a prolonged developmental period in the resistant chickpea varieties (Ahmad et al., 2017). Per cent seed damage was higher in lablab (93.33%) followed by cowpea (85.83%), which also recorded maximum weight loss (29.95%). The seed damage and weight loss had a prominent association with the adult emergence rates. Tripathi et al., (2020) also found a significant positive relationship between adult emergence and percent seed weight loss. Based on SI, different pulses seeds were categorized and mentioned in Table 1. B. Biophysical seed characters The results of qualitative and quantitative seed characters are presented in Table 3. There is a variation in seed coat colour among the different pulses seeds, however most of them had smooth texture and shiny lustre. The current findings revealed that seed coat colour did not have any impact on C. phaseoli oviposition, because there was no variation in the number of eggs laid on the light as well as dark coloured pulses seeds. In contrast, Esen et al. (2019) observed that seed colour of peas influenced the oviposition by C. chinensis, wherein black and brown coloured varieties had significantly lesser number of eggs per seed than yellow and green varieties. Seed lustre also had no effect on the oviposition. This finding contrasted with Duraimurugan et al., (2014), they reported that small and shiny green gram seeds had fewer eggs compared to the large and dull seeds. The seed texture of pulses seeds used in this study did not show much variation as most of them had smooth texture, except chickpea (Desi and kabuli type) and blackgram. The roughness of black gram seed could be a factor for non-preference by C. phaseoli. A similar attribute was noticed by Shaheen et al. (2006) wherein the resistant chickpea cultivars had rough and wrinkled seed coats. The quantitative seed parameters viz., seed dimensions, seed coat thickness, seed surface area and seed sphericity, all exhibited significant variations between the pulse seeds. The seed coat thickness was minimum in the small sized pulses seeds like blackgram, greengram, horsegram and cowpea. Chickpea (Desi type) had the maximum seed coat thickness of 0.18 mm. As far as the Seed Surface Area (SSA) is concerned, Chickpea (Kabuli type) had the maximum SSA of 307.02 mm2 and horse gram had the minimum of 31.37 mm2. Seed sphericity denotes the roundness of the seed, that is, higher the value of seed sphericity, the more spherical is the seed (Wood et al., 2012). The seed sphericity of pulses seeds ranged from 53.71% (Kidney beans brown) to 90.29% (Green peas). C. Correlation study Correlation analysis was performed to understand the influence of biophysical parameters of pulses seeds on the biology of C. phaseoli (Table 4). Surprisingly, only the ovipositional preference of bruchid had significant positive association with the seed length (r=0.803), breadth (r=0.763) and seed surface area (r=0.721). This elucidates that C. phaseoli had a high preference to larger seeds for oviposition, and it is evident that greater the seed size and area, higher is the rate of oviposition by bruchid. This is in consistent with Holay et al., (2017) who reported that the seed surface area of cowpea seeds was positively correlated with the number of eggs laid. Furthermore, the seed biophysical characters had no effect on the susceptibility of pulses. The bruchid biological parameters such as number of adults emerged, percent adult emergence, seed damage, weight loss was highly associated with one another. The SI had a significant positive correlation with number of adults emerged (r=0.735), MDP (r=0.751), percent adult emergence (r=0.931), seed damage (r=0.818), and weight loss (r=0.805). Thus, the present study infers that the major reason behind bruchid resistance in some pulses may be attributed to the seed biochemical factors or the presence of any antinutritional substances and this was found consistent with several reports (Srinivasan and Durairaj 2007; Saruchi and Thakur 2014; Swamy et al., 2020).