Biological activity of Cassia occidentalis L. against Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

In developing countries, traditional control methods are commonly used against stored-product insects and mites. In Senegal, the leaves of Cassia occidentalis L. (Caesalpiniaceae) are used to protect cowpea seeds (Vigna unguiculata L. (Walpers)) against Callosobruchus maculatus (Coleoptera: Bruchidae). The biological activity of the leaves, the seeds and oil of C. occidentalis was evaluated in controlled conditions (28 ± 2°C, 45 ± 5% r.h.) against C. maculatus. At the rate of 10% (w/w), both fresh and dry leaves as well as whole and ground seeds had no contact toxicity on the cowpea beetle. In contrast, seed oil induced an increase in mortality of C. maculatus eggs and first larval instar at the concentration of 10 ml/kg cowpea. The basis of the ovicidal and larvicidal activities are discussed in this paper. Several trials using pure compounds have highlighted that several fatty acids (linoleic, oleic and stearic) are responsible for C. occidentalis toxicity. C. occidentalis seed oil did not reduce the oviposition of C. maculatus at 10 ml/kg seed.     

Field infestation of pigeonpea (Cajanus cajan (L.) Millsp.) by Callosobruchus chinensis (L.) in Uganda

Studies were conducted in Uganda to determine the importance of field infestation of pigeonpea by bruchids, and whether or not the susceptibility of the pigeonpea pod to infestation changes during pod and seed development. A survey of farmers’ fields in the major pigeonpea growing areas in northern Uganda showed that bruchids did infest pigeonpea in the field. In all three districts surveyed (Apac, Gulu and Lira), infestation levels were similar and by one species only, Callosobruchus chinensis. Once harvested, infestation of stored seeds was four times greater than stored pods. In a separate study, caged pigeonpea pods were infested at seven different developmental stages by C. chinensis. The number of eggs laid increased with development, from pod formation to the mature yellow stage, but declined thereafter. When pods were incubated, there was no adult emergence from pods infested after they had matured and started to dry. The frequency of C. chinensis adult emergence varied significantly over time; a bimodal frequency pattern of emergence was observed from pods infested at mature green stage and, to a lesser extent at the preceding late pod filling state, suggesting the occurrence of polymorphism.     

Simulation studies on the effects of solar heat on egg-laying, development and survival of Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) in stored bambara groundnut Vigna subterranea (L.) Verdcourt

The effects of simulated solar heat on oviposition, development and survival of Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) in stored bambara groundnut, Vigna subterranea (L.) Verdcourt, were evaluated at three high temperatures (40°C, 45°C and 50°C) at a constant, low humidity (30% relative humidity). Exposure to these temperatures for 6 h significantly reduced oviposition in C. maculatus and C. subinnotatus females. Females of both species that were exposed to 50°C laid significantly fewer eggs than those exposed to 40°C; and in the case of C. maculatus, females exposed to 45°C also laid significantly fewer eggs than those exposed to 40°C. The percentage of eggs laid by females of both species that reached adulthood after exposure to 50°C for 2–6 h was significantly lower than the percentage that developed from eggs laid by females that were exposed to 40°C. No adult developed from eggs of C. maculatus exposed for 6 h at 50°C or from eggs of C. subinnotatus exposed for 2 h at this temperature. For both species, no adult progeny subsequently emerged from seeds harbouring first instar larvae when exposed at 50°C for 2, 4 or 6 h. Older larvae of C. maculatus were more tolerant of exposure at 50°C: 26.8, 10.2 and 0.9% of late instar larvae exposed for 2, 4 and 6 h, respectively, developed to the adult stage. In contrast, no adults of C. subinnotatus emerged from seeds harbouring late instar larvae when exposed at 45°C for 6 h nor in seeds exposed to the temperature of 50°C for 4 or 6 h. On average, immature stages of C. subinnotatus were more susceptible to heat treatment than those of C. maculatus.     

Resistance to Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in pigeonpea (Cajanus cajan (L.) Millsp.) and other Cajanus species

Seeds of 24 accessions of pigeonpea (Cajanus cajan (L.) Millsp.) and four other species of Cajanus (formerly Atylosia) were evaluated for their resistance to infestation by Callosobruchus maculatus (F.). None of the pigeonpea accessions was resistant but resistance was evident in three species of Cajanus. In C. platycarpus most of the larvae failed to enter the hard seed coats but the few which did enter the seeds, developed normally. Adults did not emerge from the seeds of C. scarabaeoides, even though most of the larvae entered the seeds. In A. sericeus, the number of larvae entering the seeds as well as adult emergence was significantly reduced.     

Biology of an egg parasite of Callosobruchus maculatus (Fab.) (Coleoptera: Bruchidae)

Uscana mukerjii (Mani) (Chalcidoidea, Trichogrammatidae) parasitizes eggs of Callosobruchus maculatus. Mated adult U. mukerjii lived for 5.0 ± 0.8 and 4.7 ± 0.9 days (males and females, respectively) at 27 °C. The female copulated only once, whereas males did so up to 4 times. The maximum parasitization of host eggs took place within the first 24 hours of egg laying and declined thereafter. The parasite completed its development inside the host egg in 7.2 days at 27 °C and 60–63% r.h. and emerged after cutting a circular hole in the chorion of the host egg. Mated and unmated females laid 35.4 ± 1.4 and 36.0 ± 2.2 eggs in their life time of which 27.3 ± 1.8 and 23.2 ± 2.8, hatched respectively. Parasitized host eggs did not hatch and were ultimately destroyed. The degree of parasitization varied with the pulses on which the host eggs were laid. This egg parasite may be useful in controlling the populations of C. maculatus and thus help in reducing the damage caused.     

Effect of field infestations of immature pigeonpea (Cajanus cajan (L.) Millsp.) pods on production of active (flight) and sedentary (flightless) morphs of Callosobruchus chinensis (L.)

A study conducted in Uganda on Callosobruchus chinensis showed that adults emerging from dry seed-infested and immature pod-infested pigeonpea differed in a number of morphological and biological characteristics in one or both sexes. Adults emerging from dry seed-infested pigeonpea were more or less uniform in a number of these characteristics; in contrast, adults emerging from green pod-infested pigeonpea differed depending upon when they emerged: the differences were greatest between those emerging during the 2nd to the 6th days from first emergence, and those emerging from the 8th to the last days of emergence. In one or both sexes, these differences were expressed in terms of elytral hue and size, body length, distance between the compound eyes, length of pygidium, body water content, pre-maturation periods, fecundity and adult longevity. We suggest that these differences are due to polymorphism, and specifically the predominance of flight forms among late emergers from pod-infested pigeonpea. The differences observed in the two morphs of C. chinensis and ascribed to the flight and flightless forms, are thought to be adaptations for survival and propagation under field and storage conditions, respectively. The predominance of emerged adults of the flightless forms from dry seed and the flight forms from green pods were associated with low moisture content in dry seed and high moisture content in green pods, respectively. These observations show that bruchid control measures are needed in the field as well as in storage.     

Efficacy of protectants against Callosobruchus phaseoli (Gyll.) and C. maculatus (F.) (Coleoptera: Bruchidae) in mungbeans

The organophosphorus (OP) compounds chlorpyrifos-methyl, fenitrothion, methacrifos and pirimiphos-methyl, synthetic pyrethroids (SP) deltamethrin and permethrin, and the insect growth regulator (IGR) fenoxycarb were evaluated as protectants against Callosobruchus phaseoli (Gyll.) and C. maculatus (F.) in mungbeans (Vigna radiata (L.) Wilczek). Treated mungbeans were sampled for efficacy testing using C. phaseoli after various periods of storage in hot and humid conditions (30°C, 70% r.h.). Minimum effective application rates were determined for different periods of protection. During storage the OP compounds (chlorpyrifos-methyl, fenitrothion, methacrifos and pirimiphos-methyl) lost activity against C. phaseoli much faster than the SPs (deltamethrin and permethrin) and the IGR (fenoxycarb). Tests were carried out on mungbeans which were infested with C. phaseoli before treatment with pirimiphos-methyl, fenoxycarb or deltamethrin. These tests showed that immature insects in the treated beans were protected from insecticides. Finally, freshly-treated mungbeans were exposed to C. maculatus for comparison with the results for C. phaseoli. The four OP compounds, two SPs and the IGR tended to have similar potency against C. maculatus and C. phaseoli.     

Insecticidal action of Lantana camara against Callosobruchus chinensis (Coleoptera: Bruchidae)

Aerial parts of Lantana camara were investigated for their insecticidal, antiovipositional and antifeedant activity against Callosobruchus chinensis. Petroleum ether and methanol extracts of the plant showed 10–43% mortality at 1–5% concentrations. The extracts also showed complete feeding deterrent action at 5% concentrations. Loss of fecundity was also noticed in both the extracts at higher doses. The antiovipositional values were 30 mg/100 g for petroleum ether extract and 40 mg/100 g of seed for methanol extract.     

Sensory organs involved in egg distribution in Callosobruchus subinnotatus Pic. (Coleoptera: Bruchidae)

Some Callosobruchus spp are known to distribute their eggs on the legume seeds which they infest to ensure an even distribution of food resource among the offspring. The neurosensory organs involved in the dispersion of the eggs on bambarra nuts were studied in Callosobruchus subinnotatus. The antennae were necessary for the bruchid to discriminate between seeds with or without eggs. Amputation of the antennae caused the bruchid to deposit eggs indiscriminately between the two types of seeds. Secondly, the terminal half of the antenna was found to be the site of sensory cells that locate the seeds without eggs. The labial and maxillary palpi were found to mediate the even distribution of eggs on seeds. Amputation of the palpi did not impair the ability of the beetles to identify seeds without eggs but caused considerable clustering of the eggs on a few seeds. Treatment of the tarsi with 20% hydrochloric acid which destroyed sensory cells did not impair the ability of the female beetles to avoid egg laden seeds and distribute eggs evenly on pristine seeds. Thus the tarsi were not involved in the distribution of eggs on the seeds. The role of the palpi was only fully realized in the presence of the antennae. The eyes played no role in either the location of pristine seeds or the distribution of eggs among seeds. These results were related to the observation of behavioral events that led to egg deposition on seeds.     

Intraspecific and interspecific competition in Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) on stored bambara groundnut, Vigna subterranea (L.) Verdcourt

Intraspecific competition was studied in Callosobruchus maculatus and Callosobruchus subinnotatus. Interspecific competition between the two bruchids was also studied to determine which of these species is likely to cause more damage to stored bambara groundnuts, Vigna subterranea in cases of joint infestation. Results showed that increasing the adult density up to 8 females per 10 g of bambara groundnut seeds did not significantly reduce the mean number of eggs laid per female, the number of eggs developing to the adult stage, or the weight of emerged adults of either species. The developmental period of the two species was also not significantly affected. The adult emergence curve of C. maculatus was similar to that of C. subinnotatus and was of the scramble type. C. maculatus performed better than C. subinnotatus in interspecific competition and it achieved this through a higher egg-laying ability and a higher rate of progeny production coupled with a shorter life-cycle. The implications of these findings with respect to damage and possible loss of stored bambara groundnut are discussed.     

Characterization and insecticidal properties of globulins and albumins from Luetzelburgia auriculata (Allemao) Ducke seeds towards Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

We evaluated the development of Callosobruchus maculatus growing in artificial seeds composed of Vigna unguiculata (cowpea) seed flour mixed with exogenous proteins from Luetzelburgia auriculata. Albumin and globulin fractions from Luetzelburgia auriculata were characterized in terms of protein content, amino acid composition and antimetabolic proteins (trypsin/chymotrypsin inhibitory, porcine pancreatic alpha-amylase inhibitory, lectin activity and presence of chitin-binding proteins). Both fractions were distinct in terms of protein content and diversity as determined by electrophoresis. Lectin activity was present only in the globulins. Neither fraction exhibited inhibitory activity towards porcine pancreatic alpha-amylase but trypsin inhibition was observed. Interestingly, chitin-binding proteins were detected in both protein classes. Albumins had a severe effect upon larval development and were detrimental to insect emergence (LD₅₀=0.4%) while globulins displayed slight toxicity upon larval development and no effect towards insect emergence. The presence of serine proteinase inhibitory activity and chitin binding proteins could explain, at least in part, the harmful effects on C. maculatus development while lectin activity and amino acid availability seem not to correlate with any deleterious effects. Luetzelburgia auriculata would be an interesting source of seed proteins to study behavior of C. maculatus upon infestation and genes coding for insecticidal proteins could become candidates for molecular biology programs devoted to producing transgenic seeds expressing resistance towards the beetle.     

Effect of hydroprene on Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

The effect of the insect growth regulator, hydroprene, was observed on Callosobruchus maculatus (F.). Hydroprene was applied topically to the last 2–3 sternites of unmated males and females with a micropipette. No significant decrease in fecundity was observed even with the highest dose of 0.75 μg of hydroprene, whereas the fertility of the eggs laid by treated females was affected on the first day of the oviposition period even with the lowest dose of 0.1 μg, and the effect was diluted with time. Male fertility was also affected. The emerged F₁ adults showed morphological abnormalities and the developmental period was prolonged.     

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.     

Egg distribution on seeds by Callosobruchus subinnotatus (Pic.) (Coleoptera: Bruchidae)

This study investigated the ability of the females of Callosobruchus subinnotatus (Pic.) to discriminate between seeds with differing egg loads. It established the presence of an oviposition marker in C. subinnotatus which enabled the female bruchids not only to distinguish between egg-laden and pristine control seeds, but also to assess egg loads quantitatively. Observations after the second and third days of setting up the experiments showed that the females tended to distribute eggs uniformly on the control and the treated seeds once the number of eggs on the control seeds equals that on the treated seeds. The oviposition marker was soluble in ether as egg-laden seeds could not deter oviposition after washing them twice with ether. Washing once with ether was not effective and this suggested that traces of the marker were effective in deterring oviposition. Males did not produce oviposition deterrents that could be recognised by the females. There was cross-effectiveness of the C. subinnotatus marker for the females of Callosobruchus maculatus (F.) and vice versa.     

Effect of constant temperature and humidity on oviposition and development of Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) on bambara groundnut, Vigna subterranea (L.) Verdcourt

The effect of different conditions of temperature and humidity on oviposition and development of Callosobruchus maculatus and Callosobruchus subinnotatus was investigated in the present study. Four temperatures (25°C, 30°C, 35°C and 40°C) and three humidities (30%, 60% and 90% r.h.) were evaluated on both species in pure and mixed populations on bambara groundnut (Vigna subterranea) seeds. In both pure and mixed populations, temperature influenced oviposition and progeny development of both species significantly more than humidity. Egg-laying and progeny development in C. maculatus were optimal at 35°C. In contrast, oviposition and progeny development in C. subinnotatus were optimal at 30°C. In mixed populations, where eggs were laid by females of C. maculatus and C. subinnotatus held together, more C. maculatus adults than C. subinnotatus adults were produced at the various temperatures and humidities. No adult progeny of either species developed in pure or mixed populations at 40°C. C. maculatus was more fecund than C. subinnotatus and development from egg to adult took much longer in C. subinnotatus than in C. maculatus in both pure and mixed populations. The implications of these findings for the development and survival of both species in the different agroecologies and seasons in Nigeria are discussed.     

Efficacy of essential oil of Ocimum basilicum L. and O. gratissimum L. applied as an insecticidal fumigant and powder to control Callosobruchus maculatus (Fab.) [Coleoptera: Bruchidae]

Essential oils from sweet basil, Ocimum basilicum, and African basil, O. gratissimum, (Labiatae) grown in Guinea were obtained by steam distillation. Following exposure of newly emerged adult beetles (Callosobruchus maculatus) to 12 h of fumigation using pure essential oils at a dose of 25 μl/vial, 80% mortality was recorded for O. basilicum, 70% for O. gratissimum and 0% in the control. A significant difference was observed between the responses of males and females with males exhibiting greater sensitivity. When 1 g of aromatized powder was applied to adults, a 50% lethal concentration at 48 h was found to be 65 μl/g for O. basilicum and 116 μl/g of O. gratissimum oils. The essential oils from the two plant species exhibited a significant effect both on the egg hatch rate and on the emergence of adults. The egg hatch rate was reduced to 3% with O. basilicum and 15% with O. gratissimum using an essential oil concentration of 30 μl, whereas the egg hatch rate for the control was 95%. When compared with the control (97%), adult emergence dropped to 0% with O. basilicum and to 4% with O. gratissimum. Storage bioassays were run to assess the long-term effect of powders aromatized with essential oils of Ocimum. Complete protection was observed over 3 months starting at a dose of 400 μl in the case of both oils. From a germination test, it was concluded that aromatized powders have no significant effect on the seed germination rate. After 5 d, a rate of 88% germination was seen in seeds treated with aromatized powder and protected from insects, compared with 97% for untreated seeds that were not exposed to insects.     

Repellency and toxicity of troponoid compounds against the adzuki bean beetle, Callosobruchus chinensis (L.) (Coleoptera: Bruchidae)

We compared the repellency and toxicity against adzuki bean beetles among six troponoid compounds, and examined the relationship between their structure and activity. γ-Thujaplicin showed the highest repellency against the beetles among the compounds tested, while the repellency of tropiliden was quite low. The results suggested that the keto and hydroxyl groups are important in the repellent properties of troponoid compounds. Although an isopropyl group was also important in repellency, the effect varied according to its position on the seven-member ring; the farther the isopropyl group was from the keto and hydroxyl groups, the higher the repellency became. As with its repellency effect, the toxicity of tropiliden was quite low. Tropone showed the highest toxicity among the compounds tested while its repellency was relatively low. Similar to its repellency, γ-thujaplicin showed the highest toxicity among the thujaplicins. However, the toxicities of α-thujaplicin and β-thujaplicin (hinokitiol) were similar, unlike the repellency. In summary, it appears that the toxicity of troponoid compounds does not always coincide with their repellency. Furthermore, the repellency and toxicity of a mixture of γ-thujaplicin and β-thujaplicin, whose production cost is cheaper than that of hinokitiol alone, were investigated. The mixture strongly repelled the adzuki bean beetles. We conclude that the mixture of γ-thujaplicin and β-thujaplicin is a promising repellent.     

Egg production and development of three strains of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

The numbers of eggs laid by individual females of three geographically isolated strains of C. maculatus (F.) on different numbers of cowpeas were counted. Females of strains originating in the Yemen and Brazil laid about 40 eggs when provided with a single cowpea, whilst females of a Nigerian strain laid 75. Given 40 cowpeas, females of all three strains laid between 80 and 90 eggs. Only one or two adults of the Yemen strain emerged from cowpeas irrespective of the initial number of eggs present, compared with the ten or more adults of the other two strains which emerged when the cowpea bore numerous eggs. The daily levels of oviposition did not differ among the strains when females had access to cowpeas changed daily for others bearing no eggs. The periods of development differed among the three strains, the greatest median value being 33 days in the Yemen strain where the greatest individual variation in development times was also noted. The significance of the results to the development of possible control measures for this pest is discussed.     

Characterization of new sources of mungbean (Vigna radiata (L.) Wilczek) resistance to bruchids, Callosobruchus spp. (Coleoptera: Bruchidae)

The bruchid beetles Callosobruchus chinensis (L.) and C. maculatus (F.) are destructive pests of stored mungbean (Vigna radiata (L.) Wilczek). The development of resistant mungbean varieties to manage bruchids is a major breeding objective. In the present study, we investigated the characteristics of resistance to C. chinensis and C. maculatus in two new resistant mungbean accessions V1128 and V2817, and two previously reported resistant accessions V2709 and V2802, compared to the susceptible mungbean cultivar, KPS1. Evaluation for resistance to both bruchid species using whole and decorticated seeds revealed that V1128 and V2817 were free from damage, V2709 and V2802 showed partial damage with low or moderate number of bruchids emerging from seeds, and KPS1 showed complete damage with the highest number of bruchids emerged. Comparison of the seeds harvested at seed filling, early maturity and full maturity stages revealed that the percentage of damaged seeds from resistant accessions was lower at all stages compared with KPS1. V1128 and V2817 showed complete resistance against both bruchids regardless of when their seeds were harvested, while resistance in V2709 and V2802 were most pronounced at full maturity, and KPS1 was totally damaged at all times tested. These results suggest that the chemical factor(s) conferring resistance is synthesized as early as the seed filling stage. Evaluation of resistance using artificial seeds showed that increasing the percentage of resistant seed powder adversely affected bruchid growth and development. The number of adults emerging from seeds and number of damaged seeds decreased while adult developmental period increased as the proportion of resistant seed powder increased. The weight of emerging male and female adults of C. maculatus was lighter than those from the seeds containing susceptible seed powder alone. However, C. chinensis adults were not affected by the same test. The results suggest that biochemical(s) in cotyledon tissue are responsible for the resistance and the seed coat had no protective role against the bruchids. Although all four resistant accessions evaluated are useful for mungbean breeding, V1128 and V2817 show complete resistance to both C. chinensis and C. maculatus. Thus, these two new resistant sources may be the most effective for breeding purposes.