Characterization of Callosobruchus chinensis (L.) resistance in Vigna umbellata (Thunb.) Ohwi & Ohashi

Resistance to azuki bean weevil, Callosobruchus chinensis, was studied in a series of field and laboratory experiments in two accessions of rice bean (Vigna umbellata (Thunb.) Ohwi & Ohashi), one accession of black gram (V. mungo (L.) Hepper), and one accession of mungbean, (V. radiata (L.) Wilczek). Weevil damage to immature pods of the rice bean accessions, ‘Menaga’ and ‘Miyazaki’, was significantly less than to the susceptible mungbean, VC1973A. In mature pods, the pest damage to the pod wall of Menaga was significantly higher than to VC1973A, whereas the damage to Miyazaki was similar to VC1973A. Seeds within the pods of both rice bean accessions were resistant no matter when the pods were harvested. When the insects were exposed directly on dry seeds, both rice bean accessions and a black gram accession VM2164 were resistant to them. In artificial seeds made by mixing flour of the individual resistant Vigna accessions with VC1973A and subsequently exposed to bruchid oviposition, the higher the quantity of resistant Vigna flour the lower the number of bruchids that emerged from such seeds. No bruchids emerged from artificial seeds containing crude starch fraction from the three resistant Vigna accessions when such seeds were exposed to bruchid infestation, whereas many insects emerged from the seeds containing starch of VC1973A or flour of VC1973A alone. In artificial seeds made by mixing crude protein fractions of the three resistant Vigna accessions with flour of VC1973A, as the concentration of protein increased the number of C. chinensis adults that emerged decreased. Fractionation of crude proteins into acetone-precipitable proteins and peptide and amino acid portions resulted in the loss of antibiosis effect. Artificial seeds made from purified starch-polysaccharides fraction, however, exhibited antibiosis effects if prepared from the rice bean seed of Menaga and Miyazaki but not if made from the black gram seed, VM2164.     

Electroantennogram and behavioral responses of Pteromalus cerealellae to odor stimuli associated with its host, Callosobruchus maculatus

Pteromalus cerealellae (Ashmead) (Hymenoptera: Pteromalidae) is a generalist parasitoid of the larvae of many stored-product insects, including the cowpea seed beetle, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), which live endophytically in cowpea seeds. The role of host-related semiochemicals in the host location behavior of this parasitoid was investigated using electroantennogram (EAG) and behavioral (olfactometer) techniques. Responses of mated and unmated female P. cerealellae were tested to a variety of host-related chemical stimuli including hexane extracts of uninfested cowpea seeds, (bruchid)-infested cowpea seeds, bruchid larvae (whole body or WB), larval frass, adult female bruchids (WB), and adult male bruchids (WB). All of the tested stimuli elicited significant EAG responses in unmated and mated female P. cerealellae, with mated females exhibiting a greater EAG response than unmated females to some treatments. Results from Y-tube olfactometer bioassays demonstrated a significant response of mated female P. cerealellae to extracts of uninfested cowpea seeds, infested cowpea seeds, adult female bruchids, bruchid larvae, and larval frass, but no significant response was elicited by the extract of adult male bruchids. Pair-wise comparisons of the four most attractive stimuli (i.e. uninfested seeds, infested seeds, bruchid larvae, and larval frass) in a four-way olfactometer showed preference of mated female P. cerealellae for the extract of uninfested cowpea seeds compared to larval frass extract. No significant differences were recorded between other paired treatments. These results suggest the relative importance of volatile cues from seeds (host habitat) in mediating host location by P. cerealellae.     

Screening of endemic wild Vigna accessions for resistance to three bruchid species

Several bruchid species attack stored pulses including those belonging to Vigna species.Wild Vigna accessions offer a host of useful traits for improvement of their cultivated types and hence 42 endemic wild Vigna accessions from 13 species were screened against three cosmopolitan bruchid species viz., Callosobruchus maculatus (F.), C. chinensis L. and C. analis (F.). The accessions exhibited varied reactions to three bruchid species and were categorized based on two criteria-seed damage (SD) and susceptibility index (SI). Based on SD, IC251442 accession of V. umbellata was found highly resistant, whereas accessions of V. umbellata (IC251439, PRR 2007-2 and IC251440), V. vexillata (IC248326 and IC248343), V. trilobata (JAP10-5) and V. trineriva var. bournei (IC247407) were found resistant to C. maculatus. Likewise, the accessions of V. mungo var. mungo (IC251390, IC251385 and IC251387), V. vexillata (IC248326) and V. khandalensis (Kumur local) were found highly resistant, whereas the accessions V. umbellata (IC251440), V. mungo var. mungo (IC251397), V. vexillata (IC248343) and V. dalzelliana (IC247408) were found resistant to C. chinensis. Interestingly, none of the accessions was found either highly resistant/resistant to C. analis. Based on SI, several accessions (including those susceptible on the basis of SD) recorded lower SI (<0.05) and were found resistant. A few accessions namely, V. trinervia (JAP 10–51), V. trinervia var. bournei (IC247407), V. pilosa (IC210575, IC210580 and IC210576) and V. dalzelliana (IC203864) were found resistant/moderately resistant to C. chinensis and C. maculatus, whereas the same lines were found moderately susceptible/susceptible against C. analis. The remaining accessions were found to be susceptible/highly susceptible to all bruchid species tested. These resistant lines could be further subjected to biochemical as well as molecular analysis to identify the specific seed components imparting resistance to bruchids. Simultaneously, these may be deployed in introgression breeding to develop bruchid resistant superior cultivars.     

Analysis of the insecticidal activity of methylisothiocyanate on Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) and its parasitoid Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae)

The bruchid Callosobruchus maculatus causes major losses during the storage of the seeds of Vigna unguiculata in West Africa. An endemic parasitoid, the pteromalid Dinarmus basalis is present in the stores and can reduce the increase in bruchid populations. African farmers often place in the stores the leaves of a shrub, Boscia senegalensis Lam.(Capparaceae), which release methylisothiocyanate (MITC). This compound is toxic to adult bruchids and could reduce seed losses but its influence on the bruchid natural enemy D. basalis was hitherto unknown. The susceptibility of C. maculatus and D. basalis to MITC was assessed under laboratory conditions. The susceptibility of adults of both species towards MITC were similar. After a 24 h exposure, the LC₅₀ was respectively 0.48 and 0.54 mg/l for C. maculatus and D. basalis. The ovicidal activity of this compound was high; the LC₅₀ of C. maculatus eggs was 0.04 mg/l after a 24 h exposure to MITC. High MITC concentrations only slightly affected the survival of C. maculatus during its post-embryonic development in the seeds of V. unguiculata. Gas chromatographic analysis demonstrated that 25-35% of the MITC present in the atmosphere of the experimental jars was absorbed by the seeds but concentrations inside the cotyledons were too low to influence the survival of the C. maculatus larvae. The D. basalis larvae developing at the expense of their host inside the larval galleries, were more affected by the treatment. The introduction of B. senegalensis releasing MITC in the storage systems could reduce the density of the parasitoid population and so increase the seed losses by permitting the development of the bruchid population.     

Legume type and temperature effects on the toxicity of insecticide to the genus Callosobruchus (Coleoptera: Bruchidae)

Three bruchid pest species, Callosobruchus maculatus, Callosobruchus chinensis and Callosobruchus rhodesianus, were studied for their response to insecticide toxicity taking into account the separate and interactive effects of temperature and pre-adult food. The food types used were cowpea (Vigna unguiculata) and mungbean (Vigna radiata). Callosobruchus maculatus was the most tolerant to malathion and the least affected by temperature change while C. rhodesianus was the least tolerant. Over a 4 °C range (23°, 25°, 27 °C), there was generally a significant impact of temperature on the tolerance of the three species to the insecticide. The food type on which the insects developed influenced considerably the degree of insecticide tolerance. Callosobruchus maculatus and C. chinensis populations reared on mungbean had higher tolerance to malathion than their counterparts reared on cowpea, but the opposite was observed in C. rhodesianus populations. The food influence in this study suggested an ancestral cause or fitness cost depending on the species. The interaction of food-by-temperature had no significant effect on malathion toxicity to this genus. Correlation analysis showed C. chinensis to be relatively less sensitive to insecticide concentration over the range studied compared with the other two species.     

Varietal effects of cowpea, Vigna unguiculata, on tolerance to malathion in Callosobruchus maculatus (Coleoptera: Bruchidae)

The impact of cowpea variety on the response of cowpea bruchid, Callosobruchus maculatus, to malathion was investigated. The interaction of six cowpea varieties (Adamawa Brown, Ife BPC, Ife Brown, Lilongwe, Ntcheu and NCRI-L25) with the geographical strains of C. maculatus (Brazil and Cameroon), temperature (23, 25, 27 °C) and insecticide concentration were considered. Cowpea variety (V) had an unpredictable effect on C. maculatus response to malathion. Bruchid populations produced by Ife BPC were the most susceptible to malathion while those yielded by NCRI-L25 were the most tolerant. Regardless of the cowpea variety, the Brazil strain showed higher tolerance than the Cameroon strain. There was significant effect of temperature (T) and insecticide concentration (C) on malathion tolerance in both strains (S). Likewise, there was significant impact of all two-way interactions on cowpea bruchid tolerance except V x C. Significant three-way interactions on C. maculatus tolerance to malathion was only observed in S × T × V and S × T × C. The predictability of changing one of the factors on the susceptibility of C. maculatus to insecticide was very low. This study suggests a need to take the insecticide tolerance of insect populations produced by novel varieties into account during plant breeding in addition to factors such as yield and resistance to insect and disease attack.     

Genetic analysis of seed resistance to Callosobruchus chinensis and Callosobruchus maculatus in cowpea

Callosobruchus chinensis (azuki bean weevil) and Callosobruchus maculatus (cowpea weevil) are the most destructive pests that cause significant losses to cowpea (Vigna unguiculata) seeds during storage. Development of cultivar(s) resistance to bruchids is a major goal in cowpea breeding program. Cowpea accession “TVu 2027” has been identified as moderately resistant to C. maculatus. Genetic studies of the seed resistance in this accession using strains of C. maculatus from Africa and America have demonstrated that the resistance is controlled by one or two recessive genes. However, there is no reports on genetics of the resistance to C. chinensis and to strain(s) of C. maculatus from Asia. Therefore, the objective of this study was to investigate genetics of the resistance to C. chinensis and C. maculatus in TVu 2027. TVu 2027 (P₂) and PK2015VTN001 (P₁; susceptible cowpea) were used to develop six basic generations (populations), viz. P₁, P₂, F₁ (P₁ × P₂), F₂ (P₁ × P₂), BC₁P₁ (P₁ × F₁) and BC₁P₂ (P₂ × F₁). The population were evaluated for percentage of damaged seeds (PDS) and area under the disease progress stairs (AUDPS; indicating infestation severity) by C. chinensis and C. maculatus. The results showed that TVu 2027 was moderately resistant to both bruchid species. Broad-sense heritability for PDS and AUDPS was moderate, being 70% and 73% for C. chinensis, respectively, and 64% and 61% for C. maculatus, respectively. Number of genes controlling C. chinensis resistance and C. maculatus resistance was two genes and one gene, respectively. Generation mean analysis revealed that genes with additive effect and additive × dominance gene interaction are involved in the resistance to both bruchid species. Correlation analysis suggested that the genes controlling resistance to C. chinensis and those conferring resistance to C. maculatus are unlinked.     

Resistance determination of a South Indian bruchid strain against rice bean landraces of Manipur (India)

Rice bean (Vigna umbellata) is one of the under-exploited tropical food legumes. It is regarded as a potentially valuable multipurpose (grain, fodder and green manure) crop among farmers in the marginal hill areas of North-Eastern India, Manipur in particular. Rice bean seeds are comparatively resistant to storage grain pests including bruchids (Callosobruchus spp.), which generally damages other pulses of the same genus Vigna and related legumes. However, there are reports of seed infestation by bruchids during storage. The present investigation involved subjecting seeds of rice bean landraces from Manipur to low and high bruchid infestation levels in order to determine their reaction. This is the first report on bruchid bioassay conducted on landraces of this remotely situated Indian state. The landraces were classified based on the seed damage per cent with 1–9 score. Although variations in oviposition response were observed among the landraces, regression and correlation studies between seed characteristics and bruchid life parameters suggested no significant role of antixenosis (non-preference) mechanism in imparting resistance to bruchids. To date, rice bean has not been subjected to systematic breeding, despite the species' many useful characteristics. The experiments revealed identification of new sources of bruchid resistance. Hence, these landraces can be effectively used as promising donors for hybridization in pulse improvement programmes.     

Seed coat has no value in protecting cowpea seed against attack by Callosobruchus maculatus (F.)

Experiments were conducted to compare the oviposition preference of the cowpea seed beetle Callosobruchus maculatus (F.) on 22 cowpea varieties, with and without seed coat. The cowpeas included five resistant, four moderately resistant and 13 susceptible varieties. Ten of the varieties had smooth seed coats while 12 were wrinkled. Mean numbers of eggs laid on smooth and wrinkled varieties were not significantly different. The survival of the bruchid was also assessed on intact and decorticated seeds of five varieties, comprising two resistant varieties “Kanannado” and “IT89KD-288”, a moderately resistant variety “IT93K-513-2” and two susceptible varieties “IT87K-941-1” and “IT89KD-374-57”. There was no correlation of resistance level with the number of eggs oviposited on cowpea varieties. Under limited and free-choice conditions, cowpea seeds with intact seed coats were preferred to decorticated seeds for oviposition. Adult emergence, mean development periods and pre-adult mortality were similar when seed coats were removed or left intact. It is concluded that the seed coat may not be a useful aspect to consider for breeding of bruchid resistance into cowpea varieties.     

Screening of chickpea accessions for resistance against the pulse beetle,Callosobruchus chinensis L. (Coleoptera: Bruchidae)

During storage, chickpea (Cicer arietinum L.) is severely attacked by some bruchid species, especially Callosobruchus chinensis L. (Coleoptera: Bruchidae), resulting in losses in quantity and nutritional quality. In the present study, three species of Cicer including five accessions of Cicer arietinum L. (three kabuli and two desi chickpeas), four accessions of C. echinospermum P.H. Davis and five accessions of C. reticulatum Ladiz. were screened for resistance to C. chinensis in both free-choice and no-choice tests in the laboratory. Resistance was evaluated by measuring oviposition (number of eggs per seed), adult emergence (number of holes per seed), damaged seed rate and seed weight loss (%). The results revealed that no eggs were laid by the bruchid females to the C. echinospermum accessions in free-choice test, but in no-choice test only two C. echinospermum accessions (AWC 304 and AWC 305) had few eggs (4.3 and 3.3 eggs/seed, respectively). The highest rate of oviposition occurred in kabuli chickpeas, especially in YAR (25.1 eggs/seed in free-choice test). The accessions exhibited a similar pattern for adult emergence like in the oviposition rates. As for damaged seed rate, no damage was observed in both tests in the C. echinospermum accessions, except AWC 304 (6.7%) in no-choice test. The highest seed damage was seen in kabuli-type accessions, being 100% in YAR and ILC 8617. Considering seed weight loss, no weight loss occurred in the C. echinospermum accessions in both tests (except, AWC 304 in no-choice test) whereas the highest weight loss was seen in the kabuli-type accession, CA 2969 (28.6%) in free-choice test and in the desi type accession, ICC 4957 (35.0%) in no-choice test. Since lower numbers of eggs were laid on hairy, wrinkled/reticulated and dark seed accessions, these features seemed to be important in the preference of the bruchid for host selection and oviposition. These results suggest that resistant varieties can be used as gene sources in breeding new cultivars resistant to C. chinensis.     

Effect of relative humidity on the susceptibility of Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) to two modified atmospheres

It is known that modified atmospheres (MA) created in a storage environment, involving high carbon dioxide (CO₂) levels (hypercarbia) or low oxygen (O₂) levels (anoxia) are detrimental to bruchid pests of grain legumes. The possibility of enhancing MA action by increasing or decreasing the relative humidity (r.h.) conditions in storage at 25±2°C was investigated against Callosobruchus maculatus (F.), a major bruchid pest of stored cowpea seeds. Mortality of eggs and adults of the bruchid in 70% CO₂ in air and 1.0% O₂ in nitrogen (N₂) was higher at 10±3% and 34±2% than at 70±2% and 90±3% r.h. Mortality of larvae and pupae of the bruchid in the atmospheres was not affected by the r.h. in storage. Development period was longer for adults emerging from bruchid eggs exposed for 12 h to these atmospheres at the lower r.h. Freshly emerged adult bruchids from treated eggs also laid fewer eggs after 12 h of exposure to these atmospheres at the lower r.h.     

Inhibition of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) development with essential oil extracted from Cymbopogon schoenanthus L. Spreng. (Poaceae), and the wasp Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae)

The control of the development of Callosobruchus maculatus was studied using a method that combined exposure to essential oil extracted from Cymbopogon schoenanthus and the introduction of a pteromalid natural enemy of the bruchid, Dinarmus basalis. The effect of the essential oil used was evaluated on all developmental stages of C. maculatus and on adults of D. basalis. At the highest concentration tested (33.3 μl/l) all adults of C. maculatus were killed within 24 h of exposure to the oil and the development of newly laid eggs and neonate larvae was also inhibited. However, the oil had variable efficacy against the bruchid instars developing inside the seeds: 5-day-old larvae (63% LI and 37% LII) of C. maculatus developing inside the seeds proving to be highly susceptible while 15-day-old insects (84% of pupae and 16% of larvae) were tolerant. Under the same conditions (33.3 μl/l), adults of D. basalis were very susceptible to oil vapours and to the residual activity of the oil after 3 or 6 days. However, the introduction of 10 pairs of adult D. basalis into a jar containing 100 hosts aged 10 days, 3 or 6 days before the oil application, gave respectively an emergence of 26 or 18 adults of the parasitoid compared to 28 in the control and there was no adult emergence of the host. The possibility of an integrated pest management strategy by using allelochemicals such as essential oils and indigenous natural enemies to control C. maculatus development in cowpea stocks is discussed.     

Seed coat tannins and bruchid resistance in stored cowpea seeds

Seeds of wild species and varieties of Vigna were screened for their tannins and α‐amylase inhibitor contents as defensive compounds against cowpea weevil. Seed coats contained condensed tannins that were positively correlated to their colour but not to their resistance against the insect. The α‐amylase inhibitors were present in different amount in cotyledons of all species analysed. Amongst the cultivated lines assayed, Vigna unguiculata TVu 2027, an accession identified as moderately resistant, was found to contain the higher amount of α‐amylase inhibitor. When wild species were considered, V luteola and V vexillata (two resistant species) showed the highest content of α‐amylase inhibitors. In addition, two cultivated accessions (Vita 7 and IT 84E‐1‐108) of cowpea seeds, both classified as susceptible accessions, showing a different degree of bruchid damage in storage, were also analysed. No α‐amylase inhibitory activity was found in cotyledons of undamaged Vita 7 seeds, while the seed coat tannin content was found to be 13 times higher in undamaged Vita 7 seeds than in IT 84E‐1‐108 infested seeds. These latter results support the hypothesis that seed coat tannins must also be considered in biochemical defence mechanisms, which can deter, poison or starve bruchid larvae that feed on cowpea seeds. Copyright © 2004 Society of Chemical Industry     

Deterrent and insecticidal properties of bean seed (Phaseolus vulgaris L.) whole meal or protein extract incorporated into the diet of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Callosobruchus maculatus, a pest that causes serious damage to chickpea Cicer arietinum, cannot develop in the seeds of Phaseolus or Vigna spp. which contain lectins. The insecticidal activity towards C. maculatus in these seeds is attributed both to lectins with specific affinity to N-acetylglucosamine, the major component of insect chitin, and to alpha-amylase inhibitors (lectin-like proteins). The insecticidal properties of bean meal or bean protein extracts from different sources towards different pest species are variable and need to be experimentally evaluated. The main objective of this study was to determine through a feeding trial on artificial chickpea seed the potential of bean seed meal from a wild bean Vigna caracalla, four varieties of Phaseolus vulgaris, and of a protein extract of P. vulgaris seed, to alter different life history traits of C. maculatus. The chickpea weevil was set up on artificial chickpea seeds containing different amounts of bean meal to observe the effects on female oviposition, percentage of development to adulthood and juvenile development time. These traits were combined in a composite index measuring the alteration of the multiplication rate of C. maculatus fed on artificial seed. The activity of lectin-like extracts was observed on chickpea artificial seed spiked with bean seed extract. Incorporation of bean flour at a rate of 10 and 20% in chickpea artificial seed significantly decreased C. maculatus female fecundity, percentage of adult emergence, and greatly increased the development time. Feeding trials with protein extracts of P. vulgaris reduced fecundity and survival of C. maculatus. Incorporation of 10% V. caracalla bean seed meal in chickpea artificial seed, reduced the multiplication potential of C. maculatus by over 90% showing that bean seed lectin extracts are worthy of further investigation for post-harvest infestation control.     

Correlation between biophysical seed characteristics of rice bean,Vigna umbellata (Fabaceae: Faboideae: Phaseoleae) and the development of Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae)

The bruchid, Callosobruchus maculatus is a serious pest of stored pulses. Four biophysical seed characteristics viz. Seed size, texture of seed surface, thickness of seed coat and seed hardness of 10 genotypes of rice bean, a wild pulse crop were investigated for assessing mechanism of resistance against C. maculatus. Oviposition preference and larval penetration in seed coat did not differ significantly among different test genotypes. Highest number of larvae which developed up to last larval/pupal instar were observed in susceptible check variety of mungbean, PAU 911 (30.00) and lowest in rice bean genotype, LRB 535 (0.83). Highest and lowest seed weight was noticed in rice bean genotype, LRB 529 (6.81 g) and PAU 911 (3.88 g), respectively. Almost similar seed coat thickness was recorded among different test genotypes. Maximum seed hardness was noted in genotype LRB 507 (6.45 kg) whereas minimum in PAU 911 (2.00 kg) among all test genotypes. Any remarkable correlation of biophysical seed characteristics of test genotypes with ovipositon, larval penetration and development of C. maculatus was not observed. Thus, biophysical seed characteristics of rice bean did not suggest to play a vital role in imparting resistance against C. maculatus.     

Resistance of Vigna unguiculata (cowpea) seeds to Callosobruchus maculatus is restricted to cotyledonary tissues

We have investigated the survival of Callosobruchus maculatus larvae when reared on resistant IT81D 1045 Vigna unguiculata seeds, whose resistance has been associated with variant forms of vicilins. Here, we present data which show that larvae of C. maculatus feeding on embryonic axis of resistant cowpea reach a mass of around 28 times higher than those feeding on cotyledonary tissues. Additionally, incorporation of 5–10% of embryonic axis flour on artificial seeds made of resistant flour restores toxicity of seeds to the bruchid. Vicilins purified from both susceptible and resistant embryonic axis had no deleterious effects either on insect development or on insect survival until a level of 4% of incorporation. In contrast, vicilins from resistant cotyledons show an LD₅₀ (50% lethal dose) and WD₅₀ (half weight dose) of 2%. Total vicilin contents of embryonic axes were around two times lower than in cotyledonary tissues, while proteolytic activities of all four proteinase classes were always higher in the former tissues. By 2D‐PAGE we visualized eight protein spots, which seem to be exclusively found on resistant cotyledons. Copyright © 2006 Society of Chemical Industry     

The influence of geographic origin and food type on the susceptibility of Callosobruchus maculatus (Fabricius) to Piper guineense (Schum and Thonn)

The tolerance of Callosobruchus maculatus from different geographical locations reared on two cowpea varieties, pale brown Ife Brown (IFBV) and dark brown IAR48 (IAR48V), to seed powder of Piper guineense (Schum and Thonn) was investigated. C. maculatus populations were collected from nine different locations across Osun state in the South Western part of Nigeria. The main and interactive effects of cowpea variety, population origin and dose on C. maculatus tolerance to P. guineense were explored. It was observed that bruchids that emerged from IAR48V had greater tolerance of P. guineense than bruchids reared on IFBV. There were significant effects (P < 0.001) of cowpea variety, population and dose, and significant interactions among these factors (except variety × dose, P > 0.05) on the response of bruchids to P. guineense. When reared on IAR48V, bruchid populations from the North-Eastern part of the state show greater tolerance to P. guineense than their counterparts from the South–West. This study underscores the importance of knowledge of the origin of the population and the cowpea variety on which C. maculatus developed when managing bruchids damage using P. guineense.     

Automatic, rapid screening of seed resistance in cowpea, Vigna unguiculata (L.) Walpers, to the seed beetle Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) using acoustic monitoring

The biomonitor technique was investigated as a rapid and automatic method for measuring the resistance of cowpea varieties to the seed beetle Callosobruchus maculatus. This technique measures the activity of internally feeding insect larvae by counting ultrasonic emissions produced as they feed. Activity throughout the development of C. maculatus larvae in known susceptible and resistant cowpea varieties was recorded. This showed details of the development of each larval instar, and showed clear differences between the resistant and susceptible cowpeas. A rapid method for comparing cowpeas was proposed in which the activity of larvae was recorded for 24 h starting 14 days after oviposition. Using this method, significant differences in activity were apparent between one susceptible and two resistant cowpea varieties. Further comparisons using a randomised block experimental design also showed a clear difference in activity between one susceptible and one known resistant cowpea variety. This experimental protocol took 21 days. It is suggested that the biomonitor offers a promising method for screening seeds for resistance to insect pests with a reduction in the time and effort required over conventional bioassay methods.     

Desiccant drying prior to hermetic storage extends viability and reduces bruchid (Callosobruchus chinensis L.) infestation of mung bean (Vigna radiata (L.) R. Wilczek) seeds

Seeds of mung bean (Vigna radiata (L.) R. Wilczek) are subject to loss of viability due to aging and damage from pulse beetles (or bruchids; Callosobruchus spp.) infestation during storage. We investigated whether seed drying using desiccants and hermetic packaging would prevent or ameliorate these consequences of storage. Sun-dried mung bean seeds at a moisture content of 10% were subjected to further drying for 72 h using five different desiccants: Drying Beads® (a zeolite-based desiccant), silica gel, sodium aluminum silicate, activated alumina, and cow-dung ash (a traditional desiccant). Seeds were subsequently stored in hermetic plastic containers in the presence of these desiccants under ambient conditions along with sun-dried seeds stored in cloth bags or in hermetic containers. In addition, parallel samples of each treatment were inoculated with one pair of bruchid beetles (C. chinensis L.) and stored under the same conditions. The seed drying treatments did not affect initial seed quality (germination percentage and seedling vigor) significantly. After storage for 9 months at ambient temperatures, seeds dried using Drying Beads, silica gel, sodium aluminum silicate and activated alumina had higher germination percentages, seedling vigor indices and soil emergence, and lower electrical conductivity (leakage upon imbibition) and fungal infestation compared to other conditions. In addition, the mung bean seeds inoculated with bruchids and stored with these effective desiccants had less damage, oviposition, and insect respiratory activity in the hermetic containers and maintained higher seed germination and seedling vigor after six months of storage compared to other treatments and controls. The results demonstrate the superior ability of desiccants to quickly and safely dry seeds prior to and during storage and the benefits of such drying and hermetic storage conditions for preventing seed deterioration and insect damage during storage.     

Biochemical basis of insect resistance in inged bean (Psophocarpus tetragonolobus) seeds

Mature seeds of the inged bean (Psophocarpus tetragonolobus) are toxic to developing larvae of a range of cosmopolitan storage Bruchidae of economic importance, including the copea seed eevil, Callosobruchus maculatus. Insect feeding trials ere carried out in hich protein fractions from seeds of inged bean ere incorporated at a range of concentrations into artificial seeds, and their effects upon development of C maculatus determined. Both albumin and globulin fractions ere toxic to the developing larvae and their toxicity correlated ith their haemagglutinating activity. Assay of Psophocarpin A, B and C fractions demonstrated Psophocarpin B to be the most insecticidal and to contain the highest haemagglutinating activity. Purified basic seed lectin as highly insecticidal to C maculatus larvae, ith an LC₅₀ value of c. 3·5 g kg^?1. The physiological level of this protein in inged bean seeds is sufficient to account for their resistance to attack by C maculatus. inged bean trypsin inhibitor as also purified and tested in artificial seeds against C maculatus. Hoever, even at concentrations in excess of tice the physiological concentration it had no deleterious effects upon development.