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.     

Effect of monoterpenoids on oviposition and mortality of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) under hermetic conditions

Monoterpeniods have been shown to cause mortality in certain stored-product insect pests. The current report investigated the prospects of using monoterpenoids as oviposition deterrents of the cowpea beetle, Callosobruchus maculatus (Fabricius), as well as in the management of populations of the beetle. The monoterpenoids investigated include E-anethole, estragole, S-carvone, linalool, L-fenchone, geraniol, γ-terpinene and DL-camphor, and at the concentrations of 66.7, 33.3, 16.7, 8.33 and 0 μL/L. Exposure of the life stages of the beetle, which included eggs, young larvae (first instar), 4th instar, pupae and adults to different concentrations of the monoterpenoids over 24 h period caused varying levels of mortality. The stages of the beetle that were the least susceptible to the monoterpenoids were the 4th instar, and the pupae, which required high concentrations of the monoterpenoids to achieve 99% mortality. The adults and the eggs exhibited the highest susceptibility to the monoterpenoids. Mated C. maculatus females that were offered cowpea seeds upon treatment with low doses (8.33 μL/L) of the monoterpenoids did not lay eggs, while control female beetles offered untreated seeds laid several eggs. However, mated C. maculatus females laid eggs on cowpea seeds treated with monoterpenoids 3 weeks before to the day of experimentation. The monoterpenoids did not exhibit residual toxicity to the cowpea beetles. These monoterpenoids could be further investigated for the postharvest management of seed beetles of grain legumes.     

Semiochemical modulation of host preference of Callosobruchus maculatus on legume seeds

Host preference of Callosobruchus maculatus (F.) on seeds of three legume cultivars, Ife-brown and black-eyed cowpeas [Vigna unguiculata L. (Walp)], and soybean (Glycine max L.), was investigated. Mated female C. maculatus showed high (90–95%) attraction to the three legume cultivars in Y-tube bioassays. However, the weevils discriminated among the cultivars in four-choice tests and showed greater attraction to Ife-brown cowpea (50%) than to soybean (30%) and black-eyed cowpea (15%). Coupled gas chromatography-electroantennography (GC-EAD) and GC–MS analyses of the headspace volatile organic compounds (VOCs) emitted by the legume seeds identified 2-ethyl hexanol as the principal EAD active component. Emission of 2-ethyl hexanol was two-fold greater in Ife-brown cowpea (∼0.54 μg g⁻¹ seeds) compared with black-eyed cowpea (∼0.23 μg g⁻¹ seeds) and soybean (∼0.21 μg g⁻¹ seeds). Synthetic 2-ethyl hexanol attracted 68% of female C. maculatus at 0.01 μg dose in Y-tube bioassays. These results demonstrated that host preference in C. maculatus is odor-mediated, and identified 2-ethyl hexanol as a potential attractant for C. maculatus.     

Insecticidal potential of a synthetic zeolite against the cowpea weevil,Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae)

The insecticidal potential of a synthetic zeolite was evaluated against the cowpea weevil, Callosobruchus maculatus (Fabricius). The synthetic zeolite was applied to concrete surfaces at 0, 2.5, 5, 10 and 20 g/m², and the mortality of adults was assessed after 1, 3, 6, 9, 12, 24, 36, 48, and 72 h at 28 °C and 65% r.h. The residual efficacy of zeolite applied at 5 g/m² was evaluated on concrete surfaces at 0, 1, 2, 3, and 4 months post-treatment. Adults of C. maculatus were exposed to cowpeas treated with zeolite at 0, 0.1, 0.5, 1, 2, 3, 4, and 5 g/kg. The number of eggs deposited on cowpea kernels and their hatchability were determined after 7 and 14 d, respectively. The cumulative adult mortality was recorded after 1, 2, 3, and 4 d, and adult progeny production after 42 d. The residual efficacy of zeolite on cowpeas was tested at 0, 1, 2 and 3 months after treatment. On concrete, zeolite applied at ≥ 5 g/m² resulted in 100% mortality of C. maculatus adults after 24–72 h of exposure. Zeolite at 5 g/m² exhibited high residual efficacy with 100% mortality of C. maculatus adults after 36 h exposure on treated surfaces for up to 4 months. The mortality of C. maculatus adults exposed to zeolite-treated cowpeas increased with increasing concentration and exposure time. The number of eggs laid by C. maculatus, number of kernels with eggs, and adult progeny production decreased with increasing zeolite concentration. Zeolite applied to cowpeas at 1 g/kg produced 100, 99 and 77% adult mortality at 1, 2, and 3 months post-treatment. Progeny production on zeolite-treated cowpeas was significantly lower than that on untreated cowpeas. These results show that the synthetic zeolite is effective on concrete surfaces and on cowpeas in controlling C. maculatus.     

Toxicological and physiological effects of allyl isothiocyanate upon Callosobruchus maculatus

This study aimed at evaluating the toxicity of allyl isothiocyanate (AITC) to adults of Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae) and its effects upon oviposition rate, population development, respiration rate, and dry mass loss in cowpea beans. The toxicity of AITC was determined by applying lethal concentrations (LC) of the compound, whereas the mortality curves were drawn by utilizing increasing concentrations of AITC (from 5.0 to 13.33 mL m⁻³ of grains). Population development was assessed through oviposition, progeny and both daily and accumulated emergence at sublethal concentrations (LC₁ = 3.81 mL m⁻³, LC ₁₀ = 5.71 mL m⁻³, LC ₃₀ = 7.67 mL m⁻³, and LC ₅₀ = 9.41 mL m⁻³). Furthermore, the loss of dry mass in grains and the respiration rate of adults when exposed to AITC (LC₁, LC₁₀, LC₃₀, and LC₅₀) were withal appraised. The values of LC ₅₀ and LC ₉₅ to adults of C. maculatus were of 9.41 and 17.85 mL m⁻³ of grains, respectively. At sublethal concentrations of AITC, the respiration oviposition, and emergence rates declined. The fumigant agent also prevented mass loss in cowpea beans. On account of that, it is safe to say that the compound has significant potential for controlling C. maculatus, inhibiting its development in storage conditions.     

Cowpea resistance and bioactivity of two diatomaceous earths against Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) on three cowpea varieties

The bruchid, Callosobruchus maculatus (F.) is the most important pest of stored cowpea in tropical climates. Experiments were conducted to evaluate the susceptibility of three cowpea varieties and the bioactivity of SilicoSec® and FossilShield® against this insect pest under ambient laboratory conditions at the contents 0, 0.5, 1, 1.5 and 2 g/kg of cowpea. The Dobie susceptibility index for cowpea genotypes was estimated to compare their relative tolerance to this insect pest. Adult mortality was assessed after 1, 2, 4 and 6 days of exposure followed by the evaluation of the F₁ progeny. Population increase, percentage seed damage and weight loss were assessed after three months of storage. The results showed that the CRPS and TN5-78 varieties were highly susceptible to C. maculatus, while Lori variety was moderately susceptible to the weevil. SilicoSec® and FossilShield® caused a significant and increasing bruchid mortality according to the dose rates and periods of exposure. Malathion 5% caused complete mortality after one day exposure time. SilicoSec® was more effective than FossilShield® on the three varieties of cowpea. The greatest dose of SilicoSec® and FossilShield® (2 g/kg) caused 100% mortality on all three varieties; 4 days of exposure in the Lori variety was the shortest exposure time leading to complete mortality. Regarding LD₅₀ and LD₉₅ values, it was observed that C. maculatus adults are more susceptible to SilicoSec® than to FossilShield®.The two formulations of diatomaceous earth (1.5 g/kg) reduced the F₁ progeny by more than 70%, and produced less than 10% of seed damage and weight loss for the three varieties of cowpea. The varietal resistance and the use of diatomaceous earth against C. maculatus in storage could represent an alternative to Malagrain® for the protection of the cowpea.     

Oviposition preference and development of azuki bean weevil,Callosobruchus chinensis,on five different leguminous seeds

This study was conducted to determine the oviposition preference and development of azuki bean weevil, Callosobruchus chinensis (L.) (Coleoptera: Bruchidae) on five different leguminous seeds a) cowpea cultivar Yeonbundongbu, b) white kidney bean cultivar Hwanghyubilho, c) soybean cultivar Daepung, d) mung bean cultivar Seonhwanogdu, and e) azuki bean cultivar Hongeon. A multiple-choice test and a no-choice test were conducted to record the number of eggs laid, total developmental time, number of adults emerged, and adult longevity of C. chinensis on the five different leguminous seeds. Both choice and no-choice tests revealed cowpea seed as the most preferred oviposition substrate. Total developmental time from egg to adult stage ranged from 28 to 31 days; developmental time was shortest on the cowpea. Successful development of C. chinensis was not observed on soybean or on kidney bean. Rate of adult emergence was higher on azuki and mung bean seeds with longer adult longevity of those emerged from azuki bean and cowpea. Higher egg laying preference and shorter developmental time with longer adult longevity of the beetle on cowpea probably signifies importance of physical as well as chemical attributes of the seed as an oviposition substrate other than evolutionary history of the insect.     

Trehalose and proline failed to enhance cold tolerance of the cowpea weevil,Callosobruchus maculatus (F.) (Col.: Bruchidae)

The cowpea weevil, Callosobruchus maculatus (F.) (Col.: Bruchidae) is a cosmopolitan field-to-store pest ranked as the major post-harvest pest of cowpea in tropical regions. The cold tolerance of an insect species can vary as a result of abiotic features including food resources. In this study, C. maculatus larvae were fed with proline and trehalose (10, 20, and 40 mmol) treated cowpea seeds to determine the effects of these potential cryoprotectants on the supercooling (SCP) and cold hardiness of the upcoming adult beetles. The SCPs of the control, proline-fed and trehalose-fed adults non-significantly changed from −18.2 °C for the control to −17.2 °C for trehalose-fed adults. The cold hardiness (24 h at 0, -5.0, −7.5, −10.0, and −12.5 °C) of the adults was almost the same for control and treatments. Median lethal times (LT₅₀; lethal time for 50% mortality) were 6.3, 6.0, and 5.4 h, respectively. Moreover, feeding the larvae with proline and trehalose-treated seeds did not affect the proline and trehalose contents of the adult beetles. Our results showed that C. maculatus could not tolerate subzero temperatures well above their SCP, indicating that this species might be a chill-susceptible insect.     

Genetics of bruchid (Callosobruchus maculatus Fab.) resistance in cowpea (Vigna unguiculata (L.) Walp.)

Bruchid resistance has been measured using a variety of techniques. Mean development period (MDP) and percentage adult emergence (PAE) are two of the more important traits measuring bruchid (Callosobruchus maculatus Fab.) resistance in cowpea. The objective of the study was to evaluate the genetic relationship between MDP and PAE in C. maculatus resistant cowpea. Seventy-two F₂ population plants were developed from the cross between C. maculatus resistant TVu-11953 (with delayed MDP and low PAE) and C. maculatus susceptible Ife Brown (with early MDP and high PAE) which were evaluated for resistance to cowpea C. maculatus. MDP at 45 days after infestation (DAI) and PAE at 60 DAI were taken as analysed measures for resistance to C. maculatus infestation. Data generated were subjected to chi-square analysis. Varied resistant response to C. maculatus infestation was observed among the F₂ generation plants but their responses showed inclination to the susceptible parent. A 15:1 ratio for susceptible to resistant genotypes was observed with MDP among the F₂ genotypes evaluated which is an indication of the presence of two recessive genes that control of MDP. The segregation of PAE also showed a 15:1 ratio goodness of fit (P > 0.05) for susceptible to resistant genotypes. Test of independence between MDP and PAE was not significant (χ² = 2.19, P = 0.19). This study revealed that the recessive genes controlling these two traits (MDP and PAE) were independently assorted and showed no linkage. This was also evident in the observed F₂ genotypes with C. maculatus resistance expressing either delayed MDP or low PAE and not both in the study.     

Effect of different legume seeds on life table parameters of cowpea weevil,Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae)

The cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) is one of the most important storage pests of legume seeds. The effect of various legume species including chickpea (Cicer arietinum L.) (cultivars Hashem and Mansour), cowpea (Vigna unguiculata L.) (cultivars Mashhad and 1057), green gram (Vigna radiata L.) (cultivar Parto), lentil (Lens culinaris Medikus) (cultivar Bilehsavar) was studied on the life history and life table parameters of C. maculatus at 30 ± 1 °C, relative humidity of 65 ± 5% and complete darkness. The developmental time was longest on lentil and shortest on cowpea 1057. The fecundity (number of eggs laid per reproductive period) of the pest was the lowest on lentil. The longest oviposition period was observed on chickpea Hashem. The gross and net reproductive rates were the highest on chickpea Mansour and lowest on lentil. The intrinsic rate of increase and finite rate of increase were the lowest when C. maculatus was reared on lentil and highest when it was reared on other hosts. The longest and shortest mean generation times were observed on lentil and cowpea 1057, respectively. According to the obtained results, lentil was relatively resistant and the other tested legumes were more susceptible hosts for feeding and population increase of C. maculatus. It is concluded that the resistant host cultivar can be proposed to be incorporated into breeding programs to minimize the economic losses incurred by C. maculatus.     

Identification,biochemical characterization and biological role of defense proteins from common bean genotypes seeds in response to Callosobruchus maculatus infestation

Common bean is a legume of significant socioeconomic importance and is cultivated worldwide. This crop is affected by several pests and diseases, which cause considerable economic losses and reduce yield. In recent years, several studies have demonstrated the role of proteins and peptides with activity against a wide range of insects and pathogens. The objective of this work was to identify defense proteins, such as antimicrobial peptides, protease and amylases inhibitors in common bean genotypes and evaluate the relationship of these proteins with Phaseolus vulgaris seed resistance to Callosobruchus maculatus infestation. Nineteen common bean genotypes were subjected to protein extraction, pH 5.4, and precipitation with ammonium sulfate at 70% saturation. The obtained extracts were separated by tricine gel electrophoresis. Experiments were carried out with natural seeds of common beans and artificial seeds (Vigna unguiculata seeds covered with seed coats of common beans) to evaluate the rate of oviposition and development of the insect species Callosobruchus maculatus. Lipid-transfer proteins were identified in nine genotypes whereas defensins were present in all genotypes. The inhibitory activity of α-amylases and trypsin and fungal development were determined in crude extracts (50 μg mL⁻¹). The results also indicated that the extracts from all bean genotypes inhibited the activity of human salivary α-amylase and C. maculatus larval α-amylase. Except for the extracts of four genotypes, all other extracts inhibited trypsin activity. None of the extracts from the evaluated bean genotypes inhibited the growth of tested fungi. Natural seeds from all genotypes did not inhibit insect oviposition, however, the larvae did not survive after feeding on these seeds. Artificial seeds containing seed coat flour of all genotypes inhibited the oviposition of C. maculatus, indicating that the seed coat was also repellent to insect.     

Effects of temperature on development of the azuki bean weevil,Callosobruchus chinensis (Coleoptera: Bruchidae) on two leguminous seeds

The azuki bean weevil, Callosobruchus chinensis L., is one of the most serious stored product pests in the world. The temperature driven stage-specific development of C. chinensis was examined at eight constant temperatures of 15.97, 18.31, 22.09, 26.15, 30.50, 34.39, 38.00, and 40.00 °C on azuki bean (Vigna angularis [Wild.] Ohwi & Ohashi) and cowpea (Vigna unguiculata L.) seeds. Parameters for stage-specific development such as threshold temperatures and thermal constants were determined by linear and nonlinear models. The total developmental time (egg - adult) decreased with increasing temperature from 14 to 38 °C on both seeds. However, total developmental time varied from 127.93 to 122.25 days at 15.97 °C to 19.31 and 19.17 days at 38.00 °C on azuki bean and cowpea seeds, respectively. The nonlinear Logan-6 and Performance models estimated optimal temperatures as 37.3, 37.0, 36.5 and 37.1 °C on azuki bean, and as 36.7, 36.4, 34.5 and 36.6 °C on cowpea for egg, larva, pupa and egg to adult, respectively. The linear model estimated the lower temperature thresholds (T_min) of egg, larva, pupa and egg to adult as 16.97, 10.47, 1.36, and 10.28 °C on azuki bean, respectively, and 16.84, 10.33, 10.92, and 9.83 °C on cowpea, respectively. The thermal constants (K) for each stage completion was 35.13, 255.21, 233.11, and 503.41° days (DD) for egg, larva, pupa, and egg to adult on azuki bean, respectively and 32.45, 246.50, 107.04, and 490.02 DD for egg, larva, pupa, and egg to adult on cowpea, respectively. Temperature also influenced the adult longevity. These findings on thermal requirements and temperature thresholds can be used to predict the occurrence, number of generations and population dynamics of C. chinensis.     

Effects of chemical- and bio-fertilizers on cowpea resistance to cowpea weevil,Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae)

The cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) is a destructive pest of cowpea grains in the field and storage. Effects of two chemical fertilizers (triple superphosphate (TSP) and urea) and three bio-fertilizers (Bradyrhizobium japonicum, Pseudomonas putida and mycorrhizal fungi) compared to control were studied on resistance of cowpea pod and grain to C. maculatus. Pod resistance was evaluated as oviposition preference, egg-to-adult survival and developmental time, and grain resistance was measured as life history and life table parameters of the pest. Cowpea plants treated with tested fertilizers were grown under field condition. Then, the full-size green pods and their immature grains were harvested and used in the experiments. The highest oviposition preference and percentage of adults emergence were on control (untreated) pods as compared to treated ones. The longest developmental times were recorded on the pods obtained from TSP and B. japonicum treatments. In most cases, significant differences were observed for the life history and life table parameters of C. maculatus on the grains treated with examined fertilizers. Delayed developmental time was recorded when C. maculatus was fed with P. putida- and B. japonicum-treated grains. The highest and lowest number of eggs laid by each female (fecundity) was on the grains obtained from TSP and control treatments, respectively. The net reproductive rate (R₀), intrinsic rate of increase (r_m) and finite rate of increase (λ) were the lowest on cowpea grains fertilized with B. japonicum and highest on the grains treated with urea. Our results showed that B. japonicum can be suggested to utilize, as an alternative for chemical fertilizers, to minimize cowpea infestation by C. maculatus. These findings could be helpful in developing integrated management of the pest on cowpea.     

Resistance screening of 14 Cajanus cajan (L.) Millsp. cultivars to Callosobruchus maculatus (F.) (Coleoptera:Bruchidae)

Pigeonpea, Cajanus cajan, is a rich source of human dietary protein and carbohydrate as well as an income generator for farmers especially in developing countries. However, a major limiting factor to the viable production and post-harvest preservation of pigeonpea is infestation by the cowpea weevil, Callosobruchus maculatus. An experiment to screen for resistance in 14 newly developed C. cajan cultivars from The University of the West Indies (UWI) was conducted. The experiment compared oviposition preference based on eight parameters, namely, testa thickness, testa hardness, seed sphericity, surface area, total adult emergence, larval + pupal mortality, seed hardness and surface roughness. Four of the pigeon pea cultivars screened were resistant and could be ranked in the order of decreasing resistance as: A16 = A66PL1> A112 > A196PL2. Seed surface roughness, seed testa hardness and seed grain hardness were all found to play a major role in oviposition deterrence with seed roughness being the most effective deterrent. The results suggest that breeding for pigeonpea cultivars with rougher seed coats, harder seed testa and harder grains could enhance pigeonpea seed resistance to C. maculatus by reducing infestation and damage while in storage.     

Species diversity and relative abundance of Callosobruchus (Coleoptera: Chrysomelidae) in stored cowpea in four major agricultural produce markets in the central region,Ghana

A study was conducted to investigate species diversity and relative abundance of Callosobruchus (Coleoptera: Chrysomelidae), a major insect pest infesting stored cowpea in the central region of Ghana. Cowpea stocks from Burkina Faso, Ejura, Ghana and Niger were obtained from the markets, and held to collect adults emerging from the cowpeas. Adult Callosobruchus spp. were identified based on the pattern of their hind femora and elytra. Five species, Callosobruchus maculatus, Callosobruchus rhodesianus, Callosobruchus chinensis Callosobruchus analis and Callosobruchus subinnotatus, were identified, with C. maculatus being the most abundant.     

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.     

Effects of cowpea varietal susceptibility and low pressure on the mortality of life stages of Callosobruchus maculatus (Coleoptera: Bruchidae)

Low pressure creates a low-oxygen controlled atmosphere that can kill all developmental stages of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae). This study investigated the interaction of low pressure with seed variety to determine the susceptibility of different cowpea varieties to developmental stages of C. maculatus. Laboratory studies were performed to determine exposure periods to low pressure (32.5 ± 1.0 mm Hg) necessary to kill all life stages of C. maculatus on different cowpea varieties. The results indicated that with the exception of eggs, differences in exposure periods required to achieve 100% mortality varied with life stage and variety. The larval stages were the most susceptible, and larvae required shorter exposure periods to low pressure when reared on C. maculatus resistant varieties (24-125B-3 and IT89KD-288) than on susceptible varieties (CB-3, CB-5, CB-46 and UC-27). Analysis of variance (ANOVA) showed a significant interaction between the life stages of C. maculatus, exposure time and cowpea varieties on mortality. Integration of low pressure applications with storage of cowpea varieties resistant to C. maculatus has the potential of providing an alternative pest management tool to fumigants, which are sometimes used in protecting cowpea in storage from infestation by C. maculatus.     

Possible effects of Ultraviolet ray (UV-C) on biological traits of Callosobruchus maculatus (Col.: Chrysomelidae)

Cowpea seed beetle, Callosobruchus maculatus (F.) (Col.: Chrysomelidae), is one the most important pests of stored products worldwide, which specially distributed in the tropical and subtropical regions. In the present study, effects of different irradiation times of Ultraviolet ray (0, 10, 20, 30, 40 and 50 min) on the most important biological traits of this pest were evaluated under laboratory conditions. Our findings revealed that different irradiation times significantly affect mortality of immature stages of C. maculatus. The UV-C irradiation had no significant effects on duration of different life stages of this pest. Population growth parameters of C. maculatus were significantly affected by different treatments. The highest and lowest recorded values for net reproductive rate (R₀) were calculated at Control (38.70 offspring) and 50 min of irradiation (10.36 offspring), respectively. The calculated values for intrinsic rate of increase (r) at different treatments were significantly decreased with increasing irradiation time. The lowest value of this parameter was obtained at 40 min of irradiation (0.058 day⁻¹) and followed by 50 min (0.061 day⁻¹), while the highest value was recorded at Control (0.096 day⁻¹). Sex ratio of C. maculatus was not significantly affected at different treatments. The results of the present study can be used for further assessment of irradiation as a means to control C. maculatus.     

Storage of mung bean (Vigna radiata [L.] Wilczek) and pigeonpea grains (Cajanus cajan [L.] Millsp) in hermetic triple-layer bags stops losses caused by Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Dry mung bean and pigeonpea grains that had sustained some insect damage but fumigated before the start of the experiment were stored in triple-layer hermetic bags (Purdue Improved Crop Storage (PICS™ bags) or woven polypropylene (PP) bags for 6 months. Some of the bags were artificially infested with cowpea bruchid Callosobruchus maculatus (F.) (PICS1, PP1) while others were not (PICS0, PP0). In an additional trial, PP bags containing the grains were treated with Actellic Super^® dust before being artificially infested (PP1Ac). Moisture content, live adult C. maculatus count, grain damage, weight loss, and seed germination were determined on a monthly basis. At six months, moisture contents of grain stored in PICS and PP bags remained below 12%. Storage in PICS bags halted multiplication of C. maculatus, and the initial damage level and weight of grains did not change. Conversely, in the PP bags, C. maculatus populations increased massively and seed damage reached 71.8 ± 1.9%, 76.9 ± 0.4%, and 60.3 ± 0.6% corresponding to weight losses of 14.5 ± 0.1%, 16.5 ± 0.2% and 12.5 ± 0.1% in PP0, PP1 and PP1Ac, respectively, in mung beans. With the pigeonpeas, seed damage reached 55.1 ± 0.6%, 95.7 ± 0.4% and 75.8 ± 0.9%, corresponding to weight losses of 13.0% ± 0.3%, 26.2 ± 0.2% and 13.5 ± 0.1%, in PP0, PP1 and PP1Ac, respectively. PICS bags are an effective tool for preserving mung beans and pigeonpeas against C. maculatus attack, and their performance is superior to that of Actellic Super^® dust.     

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.