Irradiation is a physical, environmentally friendly treatment which does not leave any residues in the product. It is increasingly used as an alternative to methyl bromide and other chemical fumigants for disinfestation of insect pest in stored grains. In this research, we try to evaluate the effect of low gamma irradiation doses in the range of 50–1200 Gy on the different stages of Callosobruchus maculatus. It was found that no adults emerged after irradiation of eggs at 450 Gy. No emerging adults (F1 generation) have been shown when larvae or pupae were exposed to 650 Gy. Also, no emerging adult has been shown from the parental C. maculatus adults irradiated with 650 Gy. When suppression of F1 generation was used for the measuring effective irradiation dose and phytosanitary efficacy, 650 Gy was required for disinfestation of cowpea seed weevils. The irradiation dose level of 650 Gy was used for the large-scale confirmatory tests applied to 27,754 adults of C. maculatus in cowpea seeds resulting in non F1 adults' production with a confidence level of 93.77%. All the physical and chemical characteristics of cowpea seeds were non-significantly (P ≤ 0.05) affected by the irradiation dose of 650 Gy. Meanwhile, this irradiation dose very slightly reduced the microbial load of cowpea seeds. We recommend the generic dose 650 Gy as the phytosanitary irradiation dose for the cowpea seed weevil.

There is a need to improve research and extension documentation to assist farmers in making better use of the available resistant cowpea genotypes to insects attack during storage. A study was conducted to determine the resistance of ten cowpea genotypes [Vigna unguiculata (L.) Walp.] to Callosobruchus maculatus F. attack in the Sudano-Guinean and Sudano-Sahelian agro-ecological zones (SS) of Cameroon. Thereafter, seeds were analyzed for physical properties and chemical composition to determine the main parameters of their resistance against C. maculatus. The SS was more suitable for insect infestation. Genotypes were classified into resistant to highly susceptible. Results showed that the physical characteristics of seeds were less important than the chemical components for conferring resistance to C. maculatus. Two genotypes, Samira and Lade, consistently demonstrated high tolerance to infestation by C. maculatus, and therefore may be recommended for use in breeding programs as a source of resistance and then to minimize the dependence on insecticides for the control of insect pests under subsistence farming conditions in Cameroon.

We studied host discrimination in flight morph of Callosobruchus maculatus (F.) among the legume plants Ife-brown (IB) and black-eyed (BE) cowpea, Vigna unguiculata (L. Walp), soybean (SB), and Glycine max (L.) and analysed legume volatiles towards developing an attractant for C. maculatus. Olfactometry studies were conducted to investigate attraction of mated 3–4-day-old female C. maculatus to legume plants with the green pod (PGP), green pods (GP), plant with the ripened pod (PRP), ripened pod (RP), and plant without pod (PWP). We also assessed the response of beetles to phenological stages of the most attractive legume. In Y-tube bioassays, C. maculatus showed greater attraction to individual legumes at three phenological stages: PGP (73–93%), PRP (80–100%), and RP (63–93%) compared with PWP (6–36%). In four-choice bioassays, C. maculatus preferred IB at all stages to other legumes. SB had an insignificant attraction on the beetle. The RP of IB was the most attractive part of the plant. Gas chromatography (GC) and GC–mass spectrometry (GC–MS) analyses of volatiles emitted by RP of the legumes revealed a variation in the compositions of odour blends. Benzaldehyde was found in the volatiles of IB and BE with a higher emission in IB. Octanone was detected only in IB. The two compounds were undetected in SB volatiles. These results reveal that in addition to infesting cowpea plants at RP stage as reported in previous studies, C. maculatus could also infest cowpea plants at the GP stage.

Insecticidal activities of five pesticidal plant species, Tephrosia vogelii, Dysphania (Syn: Chenopodium) ambrosioides, Lippia javanica, Tithonia diversifolia and Vernonia amygdalina, which have been reported to control storage pests, were evaluated as leaf powders against Callosobruchus maculatus (Fabricius 1775) in stored cowpea. Their efficacy was compared with the commercial pesticide Actellic dust (pirimiphos-methyl) at the recommended concentration (50 g/90 kg), and with untreated cowpea seeds as a negative control. The plant powders were applied at concentrations of 0.01, 0.1, 1 and 3 g/10 g of cowpea seeds in 250 ml plastic containers (to measure contact toxicity), or 0.005, 0.05, 0.5 and 5 g tied in small muslin cloth bags and hung in 500 ml plastic bottles containing 10 g of cowpea seeds (to measure fumigant toxicity). Mortality of adults, oviposition deterrence, adult emergence, and percent seed damage were recorded. Complete protection of seeds and inhibition of adult emergence were achieved in Actellic dust-treated seeds; contact toxicity using leaf powders of T. vogelii at all concentrations, D. ambrosioides at concentrations of 0.1, 1 and 3 g and L. javanica at concentrations of 1 and 3 g; and fumigant toxicity using D. ambrosioides at concentrations of 0.5 and 5 g and L. javanica at a concentration of 5 g. Head space analysis of D. ambrosioides and L. javanica identified ascaridole and camphor, respectively, as components that could be responsible for the bioactivity of these plant species. These plants may, therefore, serve as effective but less harmful biopesticide alternatives to Actellic. Conversely, V. amygdalina and T. diversifolia were not effective, indicating that they should not be promoted for controlling bruchids in cowpea.

Dry grain legume seeds possessing αAI-1, an α-amylase inhibitor from common bean (Phaseolus vulgaris), under the control of a cotyledon-specific promoter have been shown to be highly resistant to several important bruchid pest species. One transgenic chickpea and four cowpea lines expressing αAI-1, their respective controls, as well as nine conventional chickpea cultivars were assessed for their resistance to the bruchids Acanthoscelides obtectus (Say), Callosobruchus chinensis L. and Callosobruchus maculatus F. All transgenic lines were highly resistant to both Callosobruchus species. A. obtectus, known to be tolerant to αAI-1, was able to develop in all transgenic lines. While the cotyledons of all non-transgenic cultivars were highly susceptible to all bruchids, C. chinensis and C. maculatus larvae suffered from significantly increased mortality rates inside transgenic seeds. The main factor responsible for the partial resistance in the non-transgenic cultivars was deduced to reside in the seed coat. The αAI-1 present in seeds of transgenic chickpea and cowpea lines significantly increases their resistance to two important bruchid pest species (C. chinensis and C. maculatus) essentially to immunity. To control αAI-1 tolerant bruchid species such as A. obtectus and to avoid the development of resistance to αAI-1, varieties carrying this transgene should be protected with additional control measures.

In West Africa, Callosobruchus maculatus Fabricius mainly develops on cowpea (Vigna unguiculata (L.) Walpers) and sometimes on Bambara groundnut (Vigna subterranea (L.) Verdcourt). A survey on the development of a C. maculatus strain selected on cowpea was undertaken during eight generations on two local varieties of Bambara to determine their level of acceptability and suitability for the pest and its evolution over time and successive generations. When C. maculatus females were in contact with seeds from both Bambara varieties for the first time, they laid fewer eggs on these hosts in comparison with cowpea. However, females that have developed inside Bambara cv. Local Beige seeds deposited more eggs on their hosts of origin from the first generation onwards. The same result was obtained on Bambara cv. Local Striped seeds from the F4 generation onwards. Egg viability was not affected by host variability. On the contrary, the larval survival was significantly reduced on Bambara seeds. Larval survival and intrinsic rates of natural increase were improved on both Bambara varieties with successive generations in comparison to cowpea. Our results demonstrate that in a non-choice situation, C. maculatus is able to develop on both Bambara cv. and even increase its reproduction potential over successive generations, regardless of the climatic variations. The results help to better understand why C. maculatus is becoming a serious concern on Bambara in West Africa where the pest is frequently in contact with this occasional host.

Insect pests cause major damage to stored grain and foodstuffs, reducing the products' weight, quality and market value. Eight spices commonly used to add flavour and colour to food were evaluated, singly and in combination, for their contact and fumigant toxicity, repellency and effects on progeny development against the cowpea weevil Callosobruchus maculatus F. and rust red flour beetle Tribolium castaneum Herbst. The powders of large cardamom, turmeric and ginger showed contact toxicity against the two test insects. Green cardamom powder was found to have fumigant toxicity against adults of both insects. Clove powder at 1.5 g/50 g dose showed 100% repellency against adults of T. castaneum. The powders of large cardamom, cinnamon and clove caused complete inhibition of progeny production in C. maculatus and T. castaneum at a dose of 5 g/100 g. A 1:1 mixture of green cardamom and turmeric showed both contact and fumigant toxicity against C. maculatus, while a mixture of clove and large cardamom showed repellency and inhibited progeny development in T. castaneum.

Development and reproductive success of the solitary egg parasitoid Uscana lariophaga Steffan were examined after development in eggs of the bruchid storage pest Callosobruchus maculatus Fabricius reared at either low or high densities on cowpea seeds and laid at day 1 and 4 of maternal life. Both bruchid larval competition and maternal age negatively affected egg size, but the latter more than the former. Uscana lariophaga reared in small hosts developed slower, were smaller and produced fewer eggs compared to parasitoids reared in large hosts. Fecundity of the parasitoid was heavily influenced by host egg size. This was reflected in the values for the intrinsic rate of increase of U. lariophaga, which differed for wasps that developed in host eggs laid by bruchid females of different age. Wasps allocated marginally more female offspring to larger hosts.

Inbreeding depression is well documented in insects but the degree to which inbreeding depression varies among populations within species, and among traits within populations, is poorly studied in insects other than Drosophila. Inbreeding depression was examined in two long-term laboratory colonies of the seed beetle, Callosobruchus maculatus (Fabricius), which are used frequently as models for experiments in ecology, evolution and behaviour. Inbreeding depression in these laboratory colonies are compared with one recently field-collected population of a different seed beetle, Stator limbatus Horn. Inbreeding reduced embryogenesis, egg hatch and larval survival in both species, such that eggs produced by sib matings were >17% less likely to produce an adult offspring. Inbred larvae also took 4–6% longer to develop to emergence in both species. Inbreeding depression varied among the measured traits but did not differ between the two populations of C. maculatus for any trait, despite the large geographic distance between source populations (western Africa vs. southern India). Inbreeding depression was similar in magnitude between C. maculatus and S. limbatus. This study demonstrates that these laboratory populations of C. maculatus harbour substantial genetic loads, similar to the genetic load of populations of S. limbatus recently collected from the field.

Effect of heating on Callosobruchus maculatus (Fabricius) in Vigna angularis (Willd.), Ohwi & Ohashi, seed was assessed using an 118° obtuse base angle solar box heater. The box heater was constructed with 1.2 mm thick sheet metal, glued inside with aluminium foil and insulated on the outside by fixing 1 cm thick polystyrene and glazed with 0.15 mm thick clear plastic sheet. Electric energy from a solar simulator panel adjusted to simulate heat trapped from natural solar energy was used. Exposure of the various developmental stages of C. maculatus infesting adzuki bean seed to heat for 45 min and more raised the temperature between and within the seeds well in excess of the lethal level (>60 °C) and resulted in complete control. Heating at 60°C of up to 3 cm adzuki bean seed (seven to eight seed layers) took about 1 h and resulted in complete control of the pest. This would enable this heater to treat large amounts of seed at a time compared with solar heaters demonstrated so far in which only a single layer of seed can be treated. Therefore, solar heating of infested adzuki bean seeds using the aforementioned box heater around noon, for 1 h, gives effective control of C. maculatus. Results of the effect of heat treatment on seed viability and moisture content showed that adzuki bean seed germination is affected by heating; hence seed meant for planting should not be heat treated to control storage insect pests. Heat treatment also did not affect seed moisture content.

Essential oils were extracted by steam distillation from Cymbopogon nardus, Cymbopogon schoenanthus and Ocimum basilicum. They were used in fumigation to investigate their absorption by cowpea, Vigna unguiculata seeds during treatment and their residual effects on adult Callosobruchus maculatus (Fabricius) survival and female reproduction, and seed germination. During the treatment, seeds absorbed the essential oil compounds differently. Treated seeds dried for 24 h and then maintained at 20, 30 and 50°C for degassing continued releasing terpenic compounds. After a 72-h exposure, adult C. maculatus mortality was less than 50% in the presence of treated and degassed seeds. The treated seeds did not affect reproduction in female C. maculatus nor seed germination.

Essential oils of three genotypes of Tagetes minuta, six of Tagetes patula and 15 of Tagetes erecta were screened for potential fumigant and contact toxicity against three stored product beetle species, Callosobruchus maculatus (Fabricius), Sitophilus oryzae (Linnaeus) and Tribolium castaneum (Herbst). Genotype 1 of T. minuta (TM-1), genotype 2 of T. patula (TP-2) and genotype 13 of T. erecta (TE-13) were the most toxic. These three genotypes were then evaluated for adult toxicity, oviposition deterrence, and ovicidal and population reduction activities. Essential oils of genotypes TM-1 and TP-2 induced 100% adult mortality for all three insect species at dosages of 50,000 ppm and 500 μg/insect in fumigant and contact toxicity bioassays, respectively. Adults of C. maculatus and S. oryzae were highly susceptible to the essential oils of the three genotypes in both fumigant and contact toxicity bioassays. The essential oil of genotype TM-1 deterred oviposition in T. castaneum by 81% and suppressed its egg hatchability by 91% when applied at a dosage of 70,000 ppm on filter paper.

The reproductive activity and the offspring development of the bruchid Callosobruchus maculatus (Coleoptera: Bruchidae) were monitored in the seeds of seven cultivars of Cicer arietinum and three cultivars of Vigna unguiculata. The number of eggs laid by the C. maculatus was higher on the V. unguiculata cultivars than on those of C. arietinum. The survival rate during the embryonic development was higher than 90% regardless of the plant species and cultivars while the post-embryonic development rates did not differ significantly between the cultivars. However, the duration of the embryonic and post-embryonic development and the weight of the emerging females varied with seed species. V. unguiculata seeds allow a higher reproduction and a better development than C. arietinum. In this study, no cultivar had been found to be resistant. In Algeria, C. maculatus can develop in stored grains of both chickpea and cowpea, and it is a major stored grain insect pest.

Powders from dry leaves of four plant species: Ficus carica (Moraceae), Eucalyptus globulus (Myrtaceae), Olea europaea (Oleacea) and Citrus limon (Rutaceae), were evaluated under controlled conditions (30±1°C and 70±5% RH), for their biological activity against Callosobruchus maculatus (Coleoptera: Bruchidae), and were compared to a powder from cloves of myrtle Syzygium aromaticum (Myrtaceae) and to eugenol (the essential oil from cloves). Once mixed with seeds of chickpea Cicer arietinum at doses of 1 to 5% (w/w), all the five powders significantly reduced adult longevity. Among these tested botanicals, clove powder was the most toxic as adult survival in treated seeds was less than 24h, even at the lowest dosage of 1%. The powders from dry leaves also reduced fecundity while that from cloves completely inhibited oviposition in C. maculatus. Indeed, the mean number of eggs laid in chickpea seeds treated with powders from dry leaves of the four plant species above varied from 273.2±30.3 to 373.8±58.2 against 401.8±37.9 in the control (untreated seeds). At the highest dose of 5%, all powders significantly reduced the number of emerging adults: 149.3±46.7 in treatment with O. europaea, 139.8±25.1 with E. globulus, 82.8±48.1 with C. limon, 31.5±20.5 in treatment with F. carica and 0.0±0.0 with S. aromaticum. Tests with lower doses (0,1–0,5%) of clove powder revealed that from the dose of 0.2% and above, C. maculatus adults died before laying eggs. Treatments with eugenol at 5μl/50g seeds (v/w), significantly reduced adult longevity (1±0.0 day), the number of eggs laid (0.0±0.0 egg) and adult emergence rate (0.0±0.0 adult), compared to the control used in this test where these parameters are respectively 7.00±0.8 days, 1134.4±204.2 eggs and 745.6±144.9 adults of the first generation.

A commercially produced palm oil brand, Palmin oil, was evaluated for its effect on eggs and larvae of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) on cowpea (Vigna unguiculata) (L.) Walp. Application of 1 μ1 of the oil on eggs deposited on 10 cowpea seeds, or directly on larvae growing inside seeds resulted in their death. Embryo mortality occurred only when the oil was placed at the anterior end of the egg. The nutritive content of cowpea seeds treated with Palmin oil remained unchanged. Furthermore, the oil did not go rancid following six months of storage.

l-menthol isolated from the essential oil of Mentha arvensis and seven of its acyl derivatives were tested for contact and vapour toxicity, and ovicidal and repellent activity against the storage pests Callosobruchus maculatus F., Rhyzopertha dominica F., Sitophilus oryzae L. and Tribolium castaneum Herbst. Menthyl propionate and l-menthol were highly toxic in contact assays and vapour toxicity assays respectively. l-menthol was also found to be strongly repellent (82–100% at 0.353 μg/cm2 dose) against all the insects, while menthyl acetate was highly ovicidal against T. castaneum.

The fumigant toxicity, ovicidal and oviposition-deterrent potential of the essential oil of Indian dill, Anethum sowa and its three major fractions against the grain beetle Callosobruchus maculatus (Coleoptera: Bruchidae) on chickpea were investigated. Two fractions produced 100% mortality of adult beetles at 3.0 μl/ml dosage, whereas the essential oil was the least effective. Fraction III was 100% ovicidal at a 70 μl/ml concentration. The essential oil and fraction III both completely deterred oviposition at the lowest concentration tested, 10 μl/ml. Neither the essential oil nor its fractions had any significant effect on chickpea seed germination.

A laboratory study was carried out to assess the effects of seed treatment and fumigation of artificially infested cowpea with the volatile oil of air-dried leaves of Ageratum conyzoides L. (Asteraceae). The oil exerted acute toxicity on adults of the cowpea weevil, Callosobruchus maculatus F. upon fumigation. Maximal mortality of 95–97% was inflicted by 60 μl oil. Application of oil dressing on cowpea seed exhibited remarkable insecticidal activity-against the weevil. Significant oviposition deterrency and complete inhibition of emergence of adult insects (F1 offspring) from oil-treated beans were evident at doses of 2.5 μl to 10 μ1/9.5 g beans. No adverse physical effects on the beans were noticed at these doses. The major isolate of the essential oil, precocene I, was four times as active as the oil.

The total number of eggs laid by Callosobruchus rhodesianus (Pic.) and Callosobruchus maculatus (F.) females in the presence of single and mixed species populations of males at different densities were counted. Increasing male density significantly reduced the realised fecundity of C. maculatus but not C. rhodesianus females. In the presence of C. maculatus males, however, the number of eggs laid by C. rhodesianus was greatly reduced. The reduction in egg laying and observations on mating behaviour indicates direct physical interference between weevils and competition for mates. An adequate number of beans were provided so competition for oviposition sites by females was unlikely. The ability of C. maculatus to inhibit oviposition of C. rhodesianus is suggested as one reason for its superiority over the latter when the two species compete for limited resources.

Some aspects of the biology of Callosobruchus maculatus (F.) on three varieties of bambara groundnut, Voandzeia subterranea (L.) Thou and a local brown cowpea variety, Vigna unguiculata (L.) Walp were studied under ambient laboratory conditions. Egg hatchability of C. maculatus was above 90% on all the legume varieties. The mean developmental period of C. maculatus ranged from 23.7 days on cowpea to 28.5 days on the Piele kargu variety of groundnut. The percent emergence of C. maculatus ranged from 61.1% on var. Piele kargu to 89.5% on var. Piele balgu. There was a significant difference (P < 0.05) between the damage caused to the brown cowpea and the bambara groundnut varieties. However, there were no significant differences (P > 0.05) in damage among the three groundnut varieties. In experiments to assess the insecticidal potential of three plant materials against C. maculatus, Azadirachta indica (neem) seed powder showed a higher efficacy than both Citrus sinensis peel powder and the powder of Chromolaena odorata leaves. At 1.0 g per 40 g of legume seed, it was twice as effective as Ci. sinensis and Ch. odorata over a period of 40 days.