Bruchid Population Research Articles

Efficacy of Neem and Papaya Leaf Powders on the Cowpea Bruchid Callosobruchus maculatus (Coleoptera: Chrysomelidae)

Callosobruchus maculatus Fab (Coleoptera: Chrysomelidae) is a pest that causes enormous damage to cowpea stocks. To limit this damage, farmers resort to synthetic insecticides despite their consequences on the environment and human health. The objective of this study was to evaluate the efficacy of neem and papaya leaf powders as an alternative to control C. maculatus pests of Vigna unguiculata Walp. stocks (Fabaceae). Five hundred grams (500 g) of cowpea seeds contained in one-litre glass jars were infested with 10 pairs of C. maculatus aged 24 hours. Each of the powders was used to treat the seeds at 20, 40, 60 g/kg cowpea in each jar respectively. For each dose of each biopesticide used, four batches (Batch 1, Batch 2, Batch 3 and Batch 4) were prepared and monitored after 1, 2, 3 and 4 months of storage respectively. The rate of reduction of the C. maculatus population, and the weight losses of the cowpeas, were determined. The results showed that after 4 months of cowpea storage, neem caused, at doses of 20, 40 and 60 g/kg, a significant reduction in the bruchid population by 42.58±6.97%; 79.1±5.31% and 84.27±5.7%; while at the same doses, papaya reduced the population by 14.32±4.53%; 42.18±5.83% and 64.86±8.03% compared to the negative control. No bruchids emerged from seeds treated with the synthetic insecticide (BEXTOXIN: fumigant) used at the dose of 0.25 g/kg during all storage periods. All doses significantly reduced cowpea weight losses, especially with the higher doses. Neem leaf powder was more effective than papaya leaf powder. Neem leaf powder could therefore be used as an alternative to synthetic chemicals in pest management of cowpea stocks.

Biological control of Acanthoscelides obtectus and Zabrotes subfasciatus in stored dried beans

This study assesses the feasibility of using natural enemies for the control of Acanthoscelides obtectus Say and Zabrotes subfasciatus Boheman (Coleoptera: Chrysomelidae), key pests of stored dried beans, Phaseolus vulgaris L. (Fabales: Fabaceae). The predatory mites Blattisocius tarsalis Berlese (Acari: Ascidae) and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) were able to prey on A. obtectus eggs, reducing the bruchid population by more than 60% under both controlled and warehouse conditions. Therefore, they show good potential as biological agents for controlling this pest. The larval parasitoids Anisopteromalus calandrae Howard and Lariophagus distinguendus Forster (Hymenoptera: Pteromalidae) were both moderately effective (34–38% reduction) at suppressing A. obtectus populations, but when A. calandrae was combined with B. tarsalis, a significant improvement in control efficacy (81% reduction in emergence) was observed. Therefore, the release of A. calandrae combined with B. tarsalis seems to be a promising strategy for controlling A. obtectus. Neither B. tarsalis nor A. swirskii were able to prey on Z. subfasciatus eggs. Only the parasitoid A. calandrae was moderately effective (39% reduction) at supressing Z. subfasciatus populations. Further testing is needed to identify other natural enemies that can complement the action of A. calandrae in reducing Z. subfasciatus populations.

Biological control of Callosobruchus chinensis (Coleoptera: Chrysomelidae) in stored chickpeas through the release of natural enemies

In this study, two predatory mites and two parasitoid wasps were evaluated for their effectiveness in controlling Callosobruchus chinensis (Coleoptera: Chrysomelidae), a common pest in stored chickpeas. The predatory mite Amblyseius swirskii (Acari: Phytoseiidae) preyed on the bruchid’s eggs but did not consume a large amount; the mite Blattisocius tarsalis (Acari: Ascidae) did not consume C. chinensis eggs. However, the larval parasitoids Anisopteromalus calandrae and Lariophagus distinguendus (Hymenoptera: Pteromalidae) were effective at reducing the bruchid’s larval population, producing mortality rates above 90% in controlled conditions (28 ± 2 °C, 75 ± 5% relative humidity [RH]). In tubes of 20-cm diameter filled with 9–35 kg of chickpeas, both parasitoids were able to parasitize the host at depths of 40, 100, and 150 cm, even when larvae were offered simultaneously at all depths. This indicates that parasitoids will probably be able to locate hosts at least at 150 cm of distance in a storage facility. A. calandrae was similarly effective at reducing the bruchid population at different parasitoid-to-host ratios (1:7, 1:15, 1:30, and 1:60). Moreover, A. calandrae efficiently reduced C. chinensis populations when released in 25-kg commercial polypropylene bags of chickpeas in simulated warehouse conditions (27 ± 2 °C and 65 ± 4% RH). This is the first time that A. calandrae and L. distinguendus are shown to be effective biological control agents for the integrated management of C. chinensis in stored chickpeas and can be an alternative to the application of pesticides for maintaining low bruchid population levels.

Local treatments and vacuum sealing as novel control strategies for stored seed pests in the tropics

Prevention of pests while maintaining viable seed during storage is often challenging for smallholder farmers in the tropics and subtropics. Investment in costly technologies or storage equipment is often unavailable or economically unreasonable, and alternative methods of seed storage can play a role in ensuring regional and global food security. This research evaluates whether or not vacuum sealing and locally available seed storage treatments are effective techniques to control cowpea bruchid (Callosobruchus maculatus). This research also assesses the effects of such techniques on the viability of stored Lablab (Lablab purpureus L.) seed in the humid tropics. Tested treatments included vegetable oil, pulverized bamboo charcoal, galangal powder, powdered detergent, a bleach solution, and carbaryl. Infested seed samples stored in northern Thailand under local treatment options and vacuum sealing were evaluated between May 2011 and May 2012 for bruchid presence, seed viability, and seed vigor. After 1 year of vacuum storage, seed viability was 77.6% compared with 66.5% under non-vacuum conditions. Over that period, vacuum storage successfully prevented bruchid population growth (4.9 compared with 123.3 insects per 50 seeds under non-vacuum conditions; F = 22.59, P < 0.001). By contrast, the oil treatment greatly reduced seed viability (1.3%), although it restrained bruchid population growth (3.5 compared to 97.0 insects per 50 seeds). Other local treatments (galangal powder, carbaryl, and bamboo charcoal) limited bruchid population growth (F = 8.37, P < 0.05) compared with the control, while maintaining seed viability. Seed germination duration was not affected by vacuum sealing and seed treatments but was rather influenced by changing environmental conditions throughout the trial. These seasonal changes also influenced overall insect lifecycle and seed metabolism. These results demonstrate that vacuum sealing and several locally available treatments provide novel, low-cost, appropriate seed storage options for local seed banks and smallholder farmers in the developing world, thus avoiding the use of locally rare or expensive chemicals, low temperature, or low moisture conditions.

Comparative evaluation of six storage methods for postharvest preservation of cowpea grain

Several technologies reputedly minimize losses of stored cowpea grain to bruchid beetles on low resource farms in Africa. Side by side comparison of these different postharvest storage methods can provide the basis for deciding which performs best. We compared six different technologies for cowpea storage: (1) grain mixed with ash; (2) mixed with sand; (3) fumigated with phostoxin; (4) admixed with the stems and leaves of Boscia senegalensis (Pers) Lam ex Poir, a potential botanical insecticide; (5) disinfested using a solar heater, and; (6) hermetically sealed in triple-layer plastic bags. Sampling was done at thirty-day intervals over five months of storage. Counts were made of (i) adult emergence holes, (ii) dead larvae and (iii) surviving bruchid larvae and adults. Controls, which consisted of infested cowpea grain stored in cloth bags, were damaged extensively. Boscia senegalensis-treated grain suffered similar severe damage. All other treatments suppressed bruchid population increases as was evident from the much lower counts of emergence holes and lower numbers of surviving or dead insects.

Regional and local scale metapopulation dynamics in the interaction between Callosobruchus maculatus and Anisopteromalus calandrae

Habitat structure increases the persistence of many extinction-prone resource–consumer interactions. Metapopulation theory is one of the leading approaches currently used to explain why local, ephemeral populations persist at a regional scale. Central to the metapopulation concept is the amount of dispersal occurring between patches, too much or too little can result in regional extinction. In this study, the role of dispersal on the metapopulation dynamics of an over-exploitative host–parasitoid interaction is assessed. In the absence of the parasitoid the highly vagile bruchid, Callosobruchus maculatus, can maintain a similar population size regardless of the permeability of the inter-patch matrix and exhibits strong negative density-dependence. After the introduction of the parasitoid the size of the bruchid population decreases with a corresponding increase in the occurrence of empty patches. In this case, limiting the dispersal of both species decouples the interaction to a greater extent and results in larger regional bruchid populations. Given the disparity between the dispersal rates of the two species, it is proposed that the more dispersive host benefits from the reduction in landscape permeability by increasing the opportunity to colonise empty patches and rescue extinction prone populations. Associated with the introduction of the parasitoid is a shift in the strength of density-dependence as the population moves from bottom–up towards top–down regulation. The importance of local and regional scale measurements is apparent when the role of individual patches on regional dynamics is considered. By only taking regional dynamics into account the importance of dispersal regime on local dynamics is overlooked. Similarly, when local dynamics were examined, patches were found to have different influences on regional dynamics depending on dispersal regime and patch location.

How host larval age, and nutrition and density of the parasitoid Dinarmus basalis (Hymenoptera: Pteromalidae) influence control of Acanthoscelides obtectus (Coleoptera: Bruchidae)

Choice of the targeted host developmental stage, regulation of parasitoid numbers released and introduction of food supplements are operational factors with a potential to influence the level of biological control. In a closed laboratory storage system maintained over two generations of the host, the impact of these three parameters on the control potential of the parasitoid Dinarmus basalis Rondani was investigated for high populations of larvae of Acanthoscelides obtectus (Say) feeding inside dry common bean seeds Phaseolus vulgaris. The beans were already infested with immature bruchids at the beginning of the storage period to simulate harvest conditions, characterized in a previous study. Treatments resulted in a reduction of 48-75% of the bruchid population within 16 weeks of storage. The best timing of parasitoid release was at the simulated harvest, as later releases reduced the bruchid population only by about half this percentage. Host feeding is postulated to be the key factor involved in the observed difference. The effect of increasing the number of parasitoids strongly depended on host age and food supplement. Addition of vials with honey had no direct effect on the bruchid population or on the parasitoid progeny. The ecological significance of these findings and implications for biological control are discussed.

Impact of the egg parasitoid Uscana lariophaga and the larval‐pupal parasitoid Dinarmus basalis on Callosobruchus maculatus populations and cowpea losses

AbstractIn West Africa, Uscana lariophaga Steffan (Hymenoptera: Trichogrammatidae) and Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae) parasitize the eggs and larvae, respectively, of Callosobruchus maculatus Fab. (Coleoptera: Bruchidae), an important pest of stored cowpea. The impact of the parasitoids on pest populations was evaluated in clay pots similar to the ones used in traditional storage in Niger. At the beginning of the storage period, cowpeas were infested with one density of C. maculatus and with either one or both of the parasitoid species. If the parasitoids we inoculated as single species in stores, both D. basalis and U. lariophaga significantly suppressed the bruchid population, but the former did so more effectively than the latter. A combination of D. basalis and U. lariophaga resulted in the same suppression of bruchid populations as when D. basalis was the only parasitoid. Fifteen weeks after storage, the parasitoids reduced the number of grains damaged significantly by 38–56%. The effect of inoculating single or multiple parasitoid species on C. maculatus populations in an augmentation strategy is discussed.

Susceptibility ofCallosobruchus maculatus(Coleoptera: Bruchidae) and its ParasitoidDinarmus basalis(Hymenoptera: Pteromalidae) to Sulphur-Containing Compounds: Consequences on Biological Control

In West Africa Callosobruchus maculatus F. causes major losses during storage of cowpea (Vigna unguiculata Walper). The larvae of C. maculatus are parasitized inside the seeds by Dinarmus basalis (Rondani). African farmers introduce aromatic plants into storage systems at the beginning of the storage period that release toxic volatile compounds into the headspace of the stores. The susceptibility of C. maculatus and D. basalis to two plant sulphur-containing compounds, methylisothiocyanate (MITC) and dimethyl disulfide (DMDS), was analyzed under laboratory conditions. The adults of C. maculatus and D. basalis had the same susceptibility to MITC but the parasitoid was more susceptible to DMDS than its host. The larvae were less affected by the treatments than the adults; the seed coat acts as a barrier for volatile penetration. Susceptibility to DMDS was high when the C. maculatus larvae were extracted from the seeds. DMDS was more toxic than MITC and differences in penetration inside the seeds could explain these results. The higher susceptibility of D. basalis to the treatments could have consequences on biological control in storage systems. The presence or absence of leaves of the shrub Boscia senegalensis Lamarck (Capparaceae), which release MITC into the jar atmosphere could have an impact on numbers of C. maculatus and D. basalis. When D. basalis adults were put into the storage systems in the absence of B. senegalensis leaves, successive generations of the parasitoids maintained the C. maculatus population at a low density. In the presence of B. senegalensis leaves, the D. basalis population was more affected by the treatment than its host C. maculatus and was incapable of preventing the increase in bruchid population. This traditional method appears to increase seed weight losses by limiting the efficiency of the biological control.

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 LC 50 was respectively 0.48 and 0.54 mg/l for C. maculatus and D. basalis. The ovicidal activity of this compound was high; the LC 50 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.

Biological Control of Bruchids in Cowpea Stores by Release of Dinarmus basalis (Hymenoptera: Pteromalidae) Adults

Bruchids cause major losses during cowpea storage in West Africa, Two species, Callosobruchus maculatus (F.) and Bruchidius atrolineatus (Pic), and one endemic pteromalid, Dinarmus basalis (Rondani), are present in the Bobo Dioulasso region of Burkina Faso where this study was carried out. B. atrolineatus adults emerging in the stores from December to January are in reproductive diapause and the C. maculatus population is small. Numbers of C. maculatus increase substantially from February onward when temperatures and humidity rise. The number of D. basalis is low at the beginning of cowpea storage in December and the parasitoid cannot control the C. maculatus population, which therefore causes important seed weight losses. When adults of D. basalis are introduced into the stores at regular intervals, either during the first 2 mo of storage or during the entire storage period, the parasitoids reduce the increase in C. maculatus numbers and the seed weight losses are <100 g/kg of seeds, Releases of D. basalis adults were made in stores containing varieties of cowpea which had been infested naturally in the fields before harvest or were infested artificially. The introduction of high numbers early in the storage period limited the buildup of the bruchid population even when the climatic conditions become favorable for the rapid multiplication of C. maculatus. Studies in the laboratory under controlled conditions confirmed the results obtained under natural conditions in Burkina Faso. A high ratio of parasitoids to host larvae and pupae was critical to the successful biological control. It is only when this ratio is high that C. maculatus populations can be controlled. Biological control of bruchids, using inoculation by D. basalis adults in cowpea stores at the beginning of the storage time, is possible and limits weight losses of stored seeds to <10% after 6 or 7 mo.

Influence of temperature and humidity on populations of Callosobruchus maculatus (Coleoptera: Bruchidae) and its parasitoid Dinarmus basalis (Pteromalidae) in two climatic zones of Burkina Faso

AbstractCallosobruchus maculatus (Fabricius) develops in the seeds of Vigna unguiculata in the Sahel region of Africa. The reproductive activity of this species and the development of its offspring were studied during the dry season at Ouagadougou and Bobo Dioulasso (Burkina Faso), two zones with different climatic conditions. The length of imaginal life of the females and the developmental time varied with changes in climatic conditions, the lowest values for both parameters being found at the end of the dry season when temperature and humidity increased. In the two zones, variations in the density of the bruchid populations have been studied in experimental stores. The density of the bruchid population was low at the beginning of the study and increased when temperature and humidity rose. The introduction of Dinarmus basalis (Rondani) adults to the stores caused a significant reduction in the numbers of C. maculatus adults. The density of the D. basalis populations was low from December to February and increased when temperatures and then humidity became higher. The increase of the D. basalis population and the rate of parasitism were greater at Bobo Dioulasso than at Ouagadougou. Laboratory studies have demonstrated that fecundity, duration of adult life and developmental times depend on humidity. This study has shown the importance of local climatic conditions on parasitoid reproduction and development and also in the control of bruchid populations in stores.

Pre-dispersal seed predation in Central AmericanAcacia farnesiana: factors affecting the abundance of co-occurring bruchid beetles.

Pre-dispersal seed predation of the leguminousAcacia farnesiana byMimosestes nubigens andM. mimosae (Coleoptera: Bruchidae) was investigated in Santa Rosa National Park, northwestern Costa Rica. The purpose of the study was to determine the patterns of resource utilization by the seed predators and the mechanisms causing such patterns. Immature, mature, and fallen fruits were monitored during the dry seasons of 1987 and 1988 from different shrubs and areas. Parameters describing plant size, fecundity, and relative plant isolation were measured on each shrub. No evidence of spatial or temporal segregation was found between the two species and the intensity of seed predation was independent of the variables measured from each plant.M. mimosae was scarcer and always occurred withM. nubigens. Both were present in areas with low and high densities of the host plant, and the frequency distributions of their emergences from the fruits overlapped through the fruiting season.urosigalphus sp., a hymenopteran parasitoid, represented ca. 40% of all insect emergences in 1987 and ca. 30% in 1988. This wasp attacked a greater proportion of bruchid eggs on pods on the shrub than on pods beneath it, and more on green than on mature fruits. Parasitism thus appears to select against bruchid females that oviposit at an early stage of pod maturation. The harsh conditions of the dry season, namely heat and desiccation, also accounted for a high level of bruchid pre-emergence mortality, especially in fallen fruits, where survival from egg to adult was only about 18%. Beneath the shrubs, bruchid females exhibited selectivity, ovipositing more on pods in the shade than on those exposed to direct sunlight. In contrast to parasitoids, abiotic factors probably impose a selective force against those bruchid females that oviposit at a late stage of maturation or on pods already dropped. Both bruchid species can have more than one generation during the fruiting period. The intensity of seed predation did not, however, change during the season. The data obtained in this study suggest that factors like natural enemies and severe weather are more likely to limit the bruchid population densities than intra- or interspecific competition.

Carry over of bruchid,Caryedon serratus(Olivier) (Coleoptera) from field to stores through seeds ofAcacia nilotica(L.) Willd. in India

Abstract A percentage pod damage of 6.8% in Acacia nilotica (L.) Willd. by the bruchid, Caryedon serratus (Olivier) in the field was recorded by examining exit holes on the pods. The mean number of females and males that emerged from 50 pods kept in laboratory were 1.3 and 1.2 respectively. The pods of A. nilotica gathered from the field for seed purposes were found to be infested in small numbers but the bruchid population increased during storage. The infestation of seeds and carry over to stores is not only a danger to uninfested seeds of A. nilotica and other plants, important in social forestry, but the tree also acts as secondary host for the population build‐up of C. serratus which spreads to its primary host, the groundnut, Arachis hypogea (L).

Spondias mombin is culturally deprived in megafauna-free forest

ABSTRACTIn the semi-deciduous forests of Santa Rosa National Park in the Pacific coastal lowlands of northwestern Costa Rica, the large and fast-growing tree Spondias mombin(Anacardiaceae) experiences greater than 95% post-dispersal seed predation by a bruchid beetle (Amblycerus spondiae) on its nuts that have been dispersed to any part of pristine or secondary successional forest. Nuts dispersed (by white-tailed deer) to abandoned pastures immediately adjacent to the forest suffer less than 20% post-dispersal seed predation but seedlings are killed by frequent grass fires. S. mombin displays significant recruitment of saplings and young trees only on forest edges free of fire for long intervals. The very high percent seed predation in the forest and the failure of many nuts to ever be dispersed away from the parent tree is attributed directly and indirectly to the absence of a herbivorous (frugivorous) megafauna that would have been part of the habitat of S. mombin through most of its evolutionary history. These large animals would have consumed large numbers of S. mombin fruits and thereby dispersed the nuts in such a manner as to have both led to more escape from bruchids and an overall reduction in the bruchid population density. By their defecation patterns, these mammals would also have defecated more nuts in sites of high quality for S. mombin sapling survival than is the case at present. In contemporary habitats, S. mombin is culturally deprived in that it can no longer interact with the habitats, animals and densities of animals whose selective pressures were a major force in the evolution of the tree's traits.

Observations on the effects of initial population densities in culture, and humidity on the production of ‘active’ females of Callosobruchus maculatus (F.) (Coleoptera, Bruchidae)

The effects of varying initial populations of normal females and males of Callosobruchus maculatus (F.), and of varying relative humidities, on the production of long-lived, flight-prone ‘active’ females was studied. Increased initial populations in cultures of cowpeas led to increased production of ‘active’ females and to higher ‘active’ female/normal female ratio, with an approximately curvilinear relationship of active female production to initial adult population. The significance of the ‘active’ form is further discussed and it is suggested that the build up of bruchid population in storage is a principal factor involved in ‘active’ form production. This leads to the dispersal of the insects from high density infestations and to the initiation of infestation at other field and storage sites. The development of the insects from egg to adult at 10%, 30%, 60%, 80% and 95% r.h. showed that ambient relative humidity has no apparent influence on ‘active’ form production. It is suggested that previously observed peaks in the incidence of ‘active’ forms of C. maculatus might be due principally to the production of ‘active’ forms from high density infestations after many months of storage and not to ambient temperature and humidity conditions.