Development of Ephestia kuehniella (Zeller), Plodia interpunctella (Hübner) and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) on kernels and wholemeal flours of Fagopyrum esculentum (Moench) and Triticum aestivum L.

Three stored product moth pests, Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica were reared on the following five foods: whole buckwheat with pericarp, decorticated buckwheat, wheat var. “Centauro” (kernels), wholemeal wheat flour and whole buckwheat flour. Results showed that achenes of buckwheat with pericarp are a poor food for the development of these species. A low rate of survival to adulthood for E. kuehniella and P. interpunctella was recorded, with a considerable extension of post-embryonic development. Although the mandibles of larvae are strong, they have trouble in breaking the fibrous buckwheat pericarp. It was observed that when the seed was decorticated there was a higher percentage of adults emerged. The emergence of E. kuehniella began, according to the food given, 34–42 days after the eggs were laid. The susceptibility index (s.i.) of achenes without pericarp (s.i. 9.7) was higher than that observed on wheat (s.i. 8.6). The first P. interpunctella adults were found after 29 days on wheat and after 56 days on buckwheat with pericarp. The shortest mean period of development occurred on wheat (34 days) while the longest was on buckwheat with pericarp at 81 days. The highest susceptibility index was on kernels (s.i. 12.8), the lowest one was on buckwheat with pericarp (s.i. 2.3). C. cephalonica began to emerge, according to the food given, after 40–55 days. In this case, fewer adults were recorded from buckwheat with pericarp, but no significant differences among the means of emerged adults on wheat, wholemeal wheat flour and whole buckwheat flour were observed. The longest mean period of development was recorded on wholemeal wheat flour (72 days) while the shortest was on wheat kernels (58 days). The highest value for the susceptibility index was obtained for wheat kernels (s.i. 7.4) and the lowest one for buckwheat with pericarp (s.i. 4.5).     

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.     

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.     

Comparative life history studies of four Callosobruchus species infesting cowpeas with special reference to Callosobruchus rhodesianus (Pic) (Coleoptera: Bruchidae)

A comparative study of the ecology of Callosobruchus analis (F.), C. chinensis (L.), C. rhodesianus (Pic) and two strains of C. maculatus (F.) was made at three temperatures (25, 30 and 35°C) and three relative humidities (60, 70 and 80% r.h.). The performances of C. rhodesianus and the strain of C. maculatus from Brazil were also compared at 20°C. The intrinsic rates of increase of each species at each temperature were estimated. The optimum temperature for multiplication of all species was around 30°C. Total oviposition was highest at 30°C for all species, but survival from egg to adult was highest at 25°C for C. rhodesianus and the Malawi strain of C. maculatus compared with 30°C for the others. Development of both strains of C. maculatus was fastest at 35°C, but all other species developed most rapidly at 30°C. Relative humidity in the range 60–80% had no appreciable effect on any of the biological characteristics studied. The performance of C. rhodesianus was better at 20°C than that of the Brazilian strain of C. maculatus, and the results are discussed in relation to the distribution of the two species in Africa.     

A practical trial of pyrethrins-in-oil surface sprays for the protection of bagged grain against infestation by Cadra cautella (Wlk.) (Lepidoptera, Phycitidae) in Kenya

Two formulations of synergized pyrethrins in technical white oil were tested as monthly protective sprays on stacks of fumigated bagged wheat, primarily against Cadra cautella (Wlk.) but also against Sitophilus oryzae (L) and Tribolium castaneum (Hbst.), under warm-temperate storage conditions in up-country Kenya. The formulations were: 0·4% pyrethrins with 2·0% piperonyl butoxide, applied at 50 ml/m², and 0·4% pyrethrins with 0·4% piperonyl butoxide at 20 ml/m².

Results were assessed by recording infestation in samples taken from each stack after 18 weeks storage and five spray applications.

Both treatments gave reasonably good protection against C. cautella but were not satisfactory against S. oryzae or T. castaneum. There was no evidence of any taint in bread made from the treated grain, but the higher application rate caused excessive staining of the bags.

It is concluded that satisfactory control of reinfestation by C. cautella can be expected in practice using 0·4% pyrethrins in oil with only a minimal quantity of added piperonyl butoxide, and that 20 ml/m² is a suitable rate for application to bagged produce.     

Evaluation of extracts of neem (Azadirachta indica A. Juss) for the control of some stored product pests

Laboratory investigations on the activity of neem leaf and seed extracts in water or methylated spirit on Callosobruchus maculatus, Sitophilus oryzae and Cylas puncticollis were made at 27 ± 2°C and 65 ± 5% r.h.. Field trials were conducted to determine their effectiveness as protectants of cowpeas and maize in storage at 28 ± 4°C and 82 ± 7% r.h for 5 months.

The results showed that the effectiveness of neem is affected by differences in insect behaviour. The extracts were more active as suppressants of C. maculatus than Sitophilus spp; there was no effect on C. puncticollis. All of the extracts tested resulted in a significant reduction in oviposition, % egg hatch and % adult emergence in C. maculatus and in adult emergence of Sitophilus.

Field trials showed that the extracts mostly gave good protection to cowpea against C. maculatus for 5 months, but only moderate protection to maize against S. zeamais. Seed extracts were more effective than leaf extracts.     

PCR assay for differentiating between Group I (proteolytic) and Group II (nonproteolytic) strains of Clostridium botulinum

Groups I (proteolytic) and II (nonproteolytic) C. botulinum are genetically and physiologically distinct groups of organisms, with both groups being involved with human botulism. Due to differences in spore heat resistance and growth characteristics, the two groups possess different types of human health risks through foods, drink, and the environment. The epidemiology of human botulism due to Groups I and II C. botulinum is poorly understood, largely due to insufficient characterization of disease isolates, and warrants thorough outbreak investigation with a particular attention to discrimination between the different physiological groups of C. botulinum. In this study, a PCR assay was developed to discriminate between Group I and Group II C. botulinum. The assay is based on the fldB associated with phenylalanine metabolism in proteolytic clostridia, and employs an internal amplification control targeted to conservative regions of 16S rrn in Groups I and II C. botulinum. The assay correctly identified all 36 Group I and 24 Group II C. botulinum strains, possessing a 100% exclusivity and inclusivity. The assay provides a substantial improvement in discriminating between the Groups I and II C. botulinum, which traditionally is based on a time-consuming and error-prone culture method. Differentiation between the physiological groups of C. botulinum is an essential step in investigation of human botulism outbreaks, and should be considered as a diagnostic corner-stone in order to improve our epidemiological understanding of human botulism.     

Nutritional behaviour of Trogoderma granarium Everts (Coleoptera: Dermestidae) on leguminous seeds

To make out the nature of dietary deficiencies of pulses for Trogoderma granarium, brewer's yeast was added in different proportions. Additions resulted in no improvement of the dietary values of green gram (Phaseolus aureus Roxb.), black gram (P. mungo L.), Bengal gram (Cicer arietinum L.), kabuli gram (C. arietinum L.) and cowpea (Vigna sinensis Savi.). But in soybean (Glycine max Merr.) or lentil (Lens esculenta Moench.) addition of yeast gave higher adult populations. In French bean (P. vulgaris L.) with or without yeast no adults were formed. Yeast alone proved to be a poor food, but with glucose the growth of insects improved significantly. The addition of cholesterol to lentil, or glucose to French bean greatly increased their food value. This indicated that lentil was qualitatively and/or quantitatively deficient in sterol, but the poor food value of French bean was due to the presence of non-utilizable carbohydrates in the seeds.     

Development and evaluation of sequential sampling plans for Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae) infesting farm-stored wheat

The development and evaluation of appropriate sampling plans are needed for cost-effective management of stored-product insects. Sequential sampling plans, which are based on a variable sample size, are generally more cost effective than plans based on a fixed sample size. For adults of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), we developed sequential sampling plans based on complete counts and the presence/absence of insects in 0.5 kg grain samples removed with a trier from the top 1 m of wheat stored in farm bins. Insect count data were used to develop a sampling plan for estimating the density of C. ferrugineus with a fixed level of precision. The presence/absence data were used to develop a sampling plan for classifying the C. ferrugineus infestation level relative to an action threshold. The performance of these sampling plans was evaluated (validated) using independent data sets and an IBM-PC software program specifically designed to test the plans. This is the first paper illustrating the development and evaluation of sequential sampling plans for a stored-product insect.     

The ability of Bruchidius atrolineatus (Pic) (Coleoptera: Bruchidae) to infest and damage seeds of different tropical legumes

The beetle Bruchidius atrolineatus (Pic) commonly infests and damages seeds of cowpea, Vigna unguiculata (L.) Walp. in tropical Africa. Its ability to infest and damage eight other tropical legumes, Vigna angularis (Willd.) Ohwi and Ohashi, Vigna radiata (L.) Wilczek, Voandzeia subterranea (L.) Thou., Cicer arietinum L., Lens culinaris Medik, Glycine max (L.) Merr. and two cultivars of Phaseolus vulgaris L. was determined. The beetle could not successfully complete its life cycle in seeds of V. subterranea, G. max, L. culinaris and P. vulgaris, but the others supported development to adult emergence. C. arietinum and V. radiata were as susceptible as V. unguiculata and could serve as primary or alternative hosts to the beetle.

In no-choice tests, there were no significant differences in the number of eggs laid by B. atrolineatus on each species or cultivar of legume. When simultaneously given seeds of V. unguiculata, V. angularis, V. radiata and C. arietinum, the beetle preferentially laid eggs on V. unguiculata.     

Antioxidant activity of Caryocar brasiliense (pequi) and characterization of components by electrospray ionization mass spectrometry

The Caryocar brasiliense known commonly as pequi is a tropical fruit of Brazilian Cerrado and is considered an important option of income and food for the populations living in this biome. Our previous study indicated that C. brasiliense had high total phenol content (209 g as gallic acid equivalent kg⁻¹) and excellent scavenging activity against 2,2-diphenyl-1-picrylhydrazyl radical (IC₅₀ of 9.44 μg ml⁻¹). In this study, we evaluated the highly efficient antioxidant activity of C. brasiliense using the biological relevant method of chemically induced lipid peroxidation. The half inhibition concentration did not exceed 0.8 μg ml⁻¹. In addition, polar components of pequi ethanolic extract were investigated by direct infusion electrospray ionization mass spectrometry (ESI-MS). The technique revealed the presence of important bioactive components widely reported as potent antioxidants such as gallic acid, quinic acid, quercetin, and quercetin 3-O-arabinose possibly explaining its higher antioxidant activity. This is the first report on the composition by ESI-MS of pequi extract demonstrating excellent antioxidant activity.     

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.     

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.     

Studies on the abundance of Cryptolestes turcicus (Grouv.) (Coleoptera, Cucujidae) in different machines of an English flour mill

The relative abundance of Cryptolestes turcicus (Grouv.) in eight centrifugals of an English flour mill was studied during the months preceding the annual fumigation in each of five years. The machine which regularly supported the largest population was that containing the least nutritious stock. It also contained the dampest residues in the only year in which the moisture content of the millstocks was studied. An infestation of over 32,000 C. turcicus was found in this centrifugal on one occasion. Three additional centrifugals, replicating the function of the badly infested machine, contained large infestations and damp or moderately damp residues when examined during one year. The relative abundance of C. turcicus in these machines appeared to depend more on the moisture content of the residues than on the nutritional differences between the free-flowing centrifugal flours passing through them. Large infestations may be dependent on the moulds which develop in damp flour residues. The centrifugal sieves did not form an impassable barrier to mutant C. turcicus released into the feed of two machines.     

Inhibition of Non-proteolytic Clostridium botulinum with Lactic Acid Bacteria in Extended Shelf-Life Cook-Chill Soups

The possibility of protecting cook-chill foods with microbial cultures against the risk of botulism was demonstrated. Three commercial soups were incubated with Clostridium botulinum 17B (10³ spores/g) and protective cultures (PCs) during 10-15 days at 10°C. The PCs populations were enumerated on M17, MRS and maltose tryptic soy agar, C. botulinum—on sorbitol tryptic soy agar, botulinal toxin was detected by the immunoassay, bacteriocins—by well diffusion assay. C. botulinum did not grow in two soups with low pH (5.2-5.5) and was unaffected by the PCs. In seafood chowder (pH 6.2) C. botulinum populations reached 10⁸ cfu/g. The co-incubation with the PCs, nisin-producing Lactococcus lactis (10⁷ cfu/g) or pediocin-producing Pediococcus pentosaceus (3×10⁸ cfu/g) singularly and as a mixture, prevented toxigenesis as well as reduced the product pH to 4.8-5.0 and C. botulinum populations to undetectable levels. Color, mouth-feel, texture, flavor and the overall acceptability of seafood chowder was not affected by the presence of the PCs.     

Feeding and 20-hydroxyecdysone treatment reverses the effect of starvation on total haemocyte count in larval forms of Corcyra cephalonica (Lepidoptera)

Starvation during the larval development prevented the normally occurring increase in the total haemocyte number in Corcyra cephalonica. This effect was reversed either by resumption of feeding or by the application of exogenous 20-hydroxyecdysone.     

Laboratory studies on behavioural interactions of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) with conspecifics, synthetic pheromone and the predator Teretriosoma nigrescens (Lewes)(Coleoptera: Histeridae)

A bioassay method was devised to test the responses of adult Prostephanus truncatus (Horn) to conspecific adults or synthetic pheromone and to observe the response of the predator Teretriosoma nigrescens (Lewes) to adult or larval P. truncatus or the synthetic pheromone of this species.

The results confirmed earlier observations that male P. truncatus are the source of a pheromone attractive to both males and females, P. truncatus adults (in this case virgin females) are disinclined to leave food in response to the pheromone and maize itself is relatively unattractive to P. truncatus. For the first time it has been demonstrated that males are not attracted to females, females repel or avoid each other and males are less attracted to the naturally produced pheromone secretion than are females. In view of the fact that unmated females will not leave food to locate a calling male it was concluded that the female response to the pheromone is primarily a means of locating a food source, rather than a sexual partner. In contrast, males release their secretion to attract females.

When adult P. truncatus were tested against grains treated with the synthetic pheromone the response of males and females was apparently identical, in contrast to the lower response of males when tested against conspecific males. It seems probable that the amounts of pheromone used when testing the synthetic mixture are greater than would be produced naturally by a calling male and that this may mask the apparently lower sensitivity of males to the natural pheromone.

The pheromone of P. truncatus is known to be a kairomone for T. nigrescens, but in the bioassay this species was not attracted to synthetic pheromone and responded more strongly to empty maize grains than to adult or larval P. truncatus. It would appear that when walking, adult T. nigrescens are unwilling to approach closely to P. truncatus. The possible significance of this is discussed.     

Efficacy of ash for controlling infestations of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in stored cowpeas

Storing cowpeas, Vigna unguiculata (L.) Walpers, with ash to protect them against Callosobruchus maculatus (F.) is a traditional storage method in northern Cameroon. The amount of ash used and the details of the methodology (i.e. mixing vs layering, the source of ash used) varies among farmers. In experiments designed to simulate traditional ash-storage procedures, it was found that a minimum ratio of 3 parts of ash to 4 parts of cowpeas prevented population growth of C. maculatus and that a 3 cm layer of ash on top of stored seeds prevented infestation by adults.     

Repellent effect of pea (Pisum sativum) fractions against stored-product insects

Peas (Pisum sativum) are toxic to some stored-product insects. The repellent effect of fractions of pea seed to stored-product insects was evaluated in multiple-choice tests in which wheat kernels were dusted with fractions rich in either protein, fibre or starch at 0.001 to 10% (wt:wt). There was a negative correlation between pea protein concentration and the number of adults found in grain for Cryptolestes ferrugineus and Sitophilus oryzae, but not for Tribolium castaneum. Pea fibre repelled C. ferrugineus adults but not S. oryzae and T. castaneum. Pea starch did not repel any of the insects. One-week old and 6-week old C. ferrugineus were equally repelled by pea protein. Repellency was detectable 1 h after exposure. Cryptolestes ferrugineus and S. oryzae did not become habituated to the repellent action of pea protein even after 4 weeks of exposure. Habituation was observed, however, when C. ferrugineus was exposed to pea fibre for 4 weeks. In a two-choice bioassay (0 vs. 0.1% and 0 vs. 1% pea protein), the pea-protein-treated grain had significantly fewer insects (C. ferrugineus, S. oryzae, Sitophilus zeamais, T. castaneum, and Tribolium confusum) than untreated grain. The properties of the pea protein fractions seem well suited for developing a natural stored grain protectant.     

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.