Tyrophagus putrescentiae (Schrank) (Astigmata: Acaridae) as a new predator of Lasioderma serricorne (F.) (Coleoptera: Anobiidae) in tobacco stores in Greece

While studying Lasioderma serricorne in tobacco stores, during the years 2002 and 2003, the presence of the cosmopolitan mite species Tyrophagus putrescentiae¹ preying on live L. serricorne larvae was noted. At intervals during this 2-year period, samples of dried tobacco leaves infested with L. serricorne were taken and the rate of parasitism by the mite was measured. The percentage of L. serricorne predated by T. putrescentiae, depending on time and tobacco store, was about 20%. Tyrophagus putrescentiae is reported for the first time as a predator of L. serricorne in tobacco stores in Greece.     

Identification of female adult Lasioderma serricorne (F.) by simple external observation of the abdomen

Lasioderma serricorne (F.) adults were examined under a stereomicroscope after being placed in 70% alcohol or benzene for about 5 min. The urosternites were thus rendered transparent and the V-shaped apodeme (important sexual characteristic of the female) was made visible through simple external observation, without dissection of their abdomen.     

Contact and fumigant activities of aromatic plant extracts and essential oils against Lasioderma serricorne (Coleoptera: Anobiidae)

Methanol extracts from 30 aromatic medicinal plant species and five plant essential oils were tested for their insecticidal activities against Lasioderma serricorne (F.) adults using direct contact application and fumigation methods. Responses varied with plant material and exposure time. Good insecticidal activity against L. serricorne adults was achieved with extracts of Agastache rugosa whole plant, Cinnamomum cassia bark, Illicium verum fruit and Foeniculum vulgare fruit as well as cinnamon (C. cassia), horseradish (Cocholeria aroracia) and mustard (Brassica juncea) oils applied at 3.5 mg/cm² in a filter paper diffusion method. Over 90% mortality at 3 days after treatment was achieved with an extract of Acorus calamus var. angustatus rhizome. Cinnamon, horseradish and mustard oils, at 0.7 mg/cm², were highly toxic to the adult beetles 1 day after treatment. In a fumigation test with the beetle adults, insecticidal activity of horseradish oil, mustard oil and Foeniculum fruit extract was much more effective in closed cups than in open ones, indicating that the insecticidal activity of these materials was largely attributable to fumigant action. These naturally occurring plant extracts and essential oils could be useful for managing populations of L. serricorne.     

Life history parameters of Lasioderma serricorne (F.) as influenced by food sources

Fecundity, egg to adult survival rate, developmental time, and adult body weight of the cigarette beetle, Lasioderma serricorne (Coleoptera: Anobiidae) were evaluated on seven food sources at 28 °C. Ground chili, paprika, cayenne pepper, chewing leaf tobacco, cigar tobacco, a commercial insect bait referred to as NOW bait, and wheat flour were used to evaluate mean lifetime fecundity. The highest fecundity (52.4±4.8 eggs/female) was observed in wheat flour, whereas the lowest fecundity (5.8±0.8 eggs/female) was observed in cigar tobacco. Among the seven food sources, beetles reared in wheat flour showed the highest survival rate of 91.0±2.7%. Only 15% of the eggs laid in NOW bait developed to the adult stage. In the three food sources containing Capsicum spp. the survival rate ranged from 30% to 40%. The egg, larval, and pupal development times varied from 3 to 5, 38 to 92 and 4 to 18 d, respectively, among food sources. Body weight and adult longevity studies showed that the heavier adults also had the longest life span. Ovipositing female L. serricorne appear to discriminate among different food sources. Although L. serricorne laid eggs in all food sources evaluated, larval and pupal survival were lowest in NOW bait. Information on the biology and host use pattern of L. serricorne may help to explain how various stored commodities are affected by this species and may lead to develop appropriate pest management strategies for this insect pest.     

Comparison of trapping efficacy for Lasioderma serricorne (F.) adults with electric, pheromone, food attractant and control-adhesive traps

During July, August, September and October 1997, in three tobacco stores in the area of Thessaloniki, four types of adhesive traps: electric (black light), pheromone (serricornin and anhydroserricornin), food attractant and control, were used for trapping Lasioderma serricorne (F.) (Coleoptera: Anobiidae). All traps had the same adhesive area based on 29.5×21 cm² polyethylene sheets. Five replicate comparisons of the four trap types took place. The electric trap caught 8912, the pheromone trap 6608, the food attractant trap 1974 and the control 1231 L. serricorne adults. The electric adhesive trap was significantly more effective than the other traps and the control. The electric trap captured a smaller number of male adults than the pheromone trap but many more females. The ratio between female and male adults was 60.15 : 39.84 for the electric trap, 8.75 : 91.25 for the pheromone trap, 51.57 : 48.42 for the food attractant trap and 43.41 : 56.58 for the control trap.     

Toxicity of carbon dioxide to drugstore beetle Stegobium paniceum and cigarette beetle Lasioderma serricorne

Mortality and sub-lethal effects of carbon dioxide (CO₂) against Stegobium paniceum and Lasioderma serricorne were studied. All life stages of S. paniceum were relatively more susceptible than those of L. serricorne. In both species, the pupal stage was the most tolerant followed by larva, egg and adult. The influence of changing CO₂ concentrations (stepwise increase or stepwise decrease) in comparison with constant CO₂ concentration on the mortality responses of adults of S. paniceum and L. serricorne at fixed Ct products was also examined. Both changing concentrations of CO₂ were more effective than constant concentration and the effect was more pronounced in S. paniceum. CO₂, at LD₅₀ doses, prolonged the developmental period of the survivors in both species. Treatment of adults caused a significant reduction in progeny production indicating an adverse effect on the multiplication potential of the survivors.     

The effect of sub-zero temperatures on different lifestages of Lasioderma serricorne (F.) and Ephestia elutella (Hübner)

The effect of sub-zero temperatures on different lifestages of Lasioderma serricorne and Ephestia elutella was investigated as a means of disinfesting stored tobacco. Eggs, unacclimated cocoons and acclimated cocoons of L. serricorne were exposed to −10 °C, −15 °C and −20 °C in insulated boxes. There was no adult emergence from eggs or unacclimated cocoons following exposure to the respective temperatures for 4 h, 2 h and 1 h. With acclimated cocoons there was no adult emergence after 2 h at −15 °C and 1 h at −20 °C, but at −10 °C, there was adult emergence after 8, 12 and 24 h exposures.In field-scale experiments, cold acclimated fourth-instar larvae of L. serricorne were inserted into cases of leaf tobacco and boxes of finished product, put into commercial freezers and exposed to minimum temperatures of −10 °C, −18 °C or −25 °C. Critical temperatures were measured at the core of the commodity. No adults emerged from the commodity when exposed to at least −18 °C for periods ranging between 3.75 h and 39.25 h or when exposed to at least −25 °C for between 2.4 h and 3.7 h. At a minimum of −10 °C, 3 live adults emerged after 24 h exposure.With E. elutella, diapausing larvae were inserted into small scale tobacco bales and exposed to −10 °C, −13 °C, −15 °C or −20 °C. No emergence of adults and no larval survival was achieved after 21 d, 3 d and 2 h exposure at −10 °C, −15 °C and −20 °C respectively. At −13 °C, there was no adult emergence after 2 and 5 d exposure, but live larvae remained after 24 weeks incubation at 25 °C.Minimum conditions of −18 °C for 24 h and −25 °C for 4 h are recommended for the control of L. serricorne and −20 °C for 24 h for the control of E. elutella in stored tobacco (to fit with operational logistics).     

Comparative study of field and laboratory evaluations of the ethnobotanical Cassia sophera L. (Leguminosae) for bioactivity against the storage pests Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

The powdered leaves of Cassia sophera along with hot- and cold-water leaf extracts of this plant were tested in laboratory experiments in the UK and in field trials in Tamale, Northern Ghana, using traditional storage containers, to determine their inhibitory and toxic effects against Sitophilus oryzae and Callosobruchus maculatus infestation of stored rice and cowpea, respectively. Laboratory and field experiments with cowpea showed that the use of C. sophera hot-water extracts was more effective at reducing C. maculatus infestation and adult emergence on cowpea than the traditional leaf-powder application (1% and 5% w/w) or the use of a cold-water extract of C. sophera. Hot-water extracts of C. sophera might be a more effective technique of applying the plant material on to stored cowpea than using powdered C. sophera leaves, the currently used application by small-scale farmers. In contrast, experiments with S. oryzae on rice showed that C. sophera leaf powder (5% w/w) effectively reduced adult emergence in the laboratory, but this could not be confirmed under field conditions. The hot and dry climatic conditions in the field might impart a natural protection against rice infestation by S. oryzae, making the use of protectants and pesticides less necessary for farmers. This was supported by the negligible rice grain damage after 6 months of field storage and by the failure of the S. oryzae population to establish itself under field conditions. The implications of using botanicals in pest control are discussed.     

Automatic, rapid screening of seed resistance in cowpea, Vigna unguiculata (L.) Walpers, to the seed beetle Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) using acoustic monitoring

The biomonitor technique was investigated as a rapid and automatic method for measuring the resistance of cowpea varieties to the seed beetle Callosobruchus maculatus. This technique measures the activity of internally feeding insect larvae by counting ultrasonic emissions produced as they feed. Activity throughout the development of C. maculatus larvae in known susceptible and resistant cowpea varieties was recorded. This showed details of the development of each larval instar, and showed clear differences between the resistant and susceptible cowpeas. A rapid method for comparing cowpeas was proposed in which the activity of larvae was recorded for 24 h starting 14 days after oviposition. Using this method, significant differences in activity were apparent between one susceptible and two resistant cowpea varieties. Further comparisons using a randomised block experimental design also showed a clear difference in activity between one susceptible and one known resistant cowpea variety. This experimental protocol took 21 days. It is suggested that the biomonitor offers a promising method for screening seeds for resistance to insect pests with a reduction in the time and effort required over conventional bioassay methods.     

Inhibition of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) development with essential oil extracted from Cymbopogon schoenanthus L. Spreng. (Poaceae), and the wasp Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae)

The control of the development of Callosobruchus maculatus was studied using a method that combined exposure to essential oil extracted from Cymbopogon schoenanthus and the introduction of a pteromalid natural enemy of the bruchid, Dinarmus basalis. The effect of the essential oil used was evaluated on all developmental stages of C. maculatus and on adults of D. basalis. At the highest concentration tested (33.3 μl/l) all adults of C. maculatus were killed within 24 h of exposure to the oil and the development of newly laid eggs and neonate larvae was also inhibited. However, the oil had variable efficacy against the bruchid instars developing inside the seeds: 5-day-old larvae (63% LI and 37% LII) of C. maculatus developing inside the seeds proving to be highly susceptible while 15-day-old insects (84% of pupae and 16% of larvae) were tolerant. Under the same conditions (33.3 μl/l), adults of D. basalis were very susceptible to oil vapours and to the residual activity of the oil after 3 or 6 days. However, the introduction of 10 pairs of adult D. basalis into a jar containing 100 hosts aged 10 days, 3 or 6 days before the oil application, gave respectively an emergence of 26 or 18 adults of the parasitoid compared to 28 in the control and there was no adult emergence of the host. The possibility of an integrated pest management strategy by using allelochemicals such as essential oils and indigenous natural enemies to control C. maculatus development in cowpea stocks is discussed.     

Progress towards a lure to attract three stored product weevils, Sitophilus zeamais Motschulsky, S. oryzae (L.) and S. granarius (L.) (Coleoptera: Curculionidae)

The behavioural responses of Sitophilus granarius, S. oryzae and S. zeamais to synthetic 4S,5R-sitophinone alone and in combination with volatiles from kibbled carob have been investigated with a view to the development of a single lure to attract all three species. Sitophilus zeamais and S. oryzae were shown to respond to 4S,5R-sitophinone at amounts as low as 0.025 ng. Sitophilus granarius gave a significant response to 50 ng 4S,5R-sitophinone. Volatiles from kibbled carob were also shown to attract all three species. This is the first time that attraction of S. zeamais and S. oryzae to carob volatiles has been demonstrated. Fresh lures containing 4S,5R-sitophinone and carob volatiles attracted significantly more insects in pitfall bioassays for all three species than when either component was used alone. However, after 6 weeks a significant increase in response compared to the control was found only for S. oryzae and S. zeamais. The effect of insect age on response to the pheromone and carob volatiles was also studied for all three species. The response to carob volatiles decreased with increasing insect age for all three species. A significant response to 4S,5R-sitophinone was found only for 1-2-day-old adults of S. oryzae and S. zeamais but for all ages tested of S. granarius. The effect of the combination of pheromone and carob volatiles also decreased with increasing insect age.     

A laboratory assessment of the potential of different strains of the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) to control Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in stored cowpea

Twelve indigenous and exotic isolates of Beauveria bassiana and Metarhizium anisopliae were evaluated for their virulence and their ability to suppress populations of Callosobruchus maculatus in stored cowpea. LT₅₀ values ranged from 3.11 to 6.12 days following immersion in aqueous suspensions containing 1×10⁸ conidia ml⁻¹. Indigenous isolates that had been recovered from C. maculatus were more virulent in laboratory bioassays than exotic isolates from other insects. The two isolates with the shortest LT₅₀ values were compared in dose-response assays by immersion and by exposure to cowpea grains treated with dry conidia. In both assays B. bassiana 0362 was consistently more virulent than M. anisopliae 0351. By immersion, LC₅₀ values on day 6 post-treatment were 9.10×10⁴ and 7.10×10⁵ conidia ml⁻¹ for B. bassiana 0362 and M. anisopliae 0351, respectively. Exposure to treated grains gave LC₅₀ values of 1.15×10⁷ and 4.44×10⁷ conidia g⁻¹ grain for B. bassiana 0362 and M. anisopliae 0351, respectively. In 1 kg batches of cowpea stocked with 50 adult C. maculatus, B. bassiana 0362 at both 1×10⁷ and 1×10⁸ conidia g⁻¹ grain led to significant adult mortality and reduced F₁ emergence relative to untreated populations. At 1×10⁸ conidia g⁻¹ the effect of the fungus persisted into the F₁ generation. The net reproductive rates, R₀, measured 26 days after insects were released were 5.16 and 7.32 for the high and low doses compared to 9.52 for the untreated control.     

Deterrent and insecticidal properties of bean seed (Phaseolus vulgaris L.) whole meal or protein extract incorporated into the diet of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Callosobruchus maculatus, a pest that causes serious damage to chickpea Cicer arietinum, cannot develop in the seeds of Phaseolus or Vigna spp. which contain lectins. The insecticidal activity towards C. maculatus in these seeds is attributed both to lectins with specific affinity to N-acetylglucosamine, the major component of insect chitin, and to alpha-amylase inhibitors (lectin-like proteins). The insecticidal properties of bean meal or bean protein extracts from different sources towards different pest species are variable and need to be experimentally evaluated. The main objective of this study was to determine through a feeding trial on artificial chickpea seed the potential of bean seed meal from a wild bean Vigna caracalla, four varieties of Phaseolus vulgaris, and of a protein extract of P. vulgaris seed, to alter different life history traits of C. maculatus. The chickpea weevil was set up on artificial chickpea seeds containing different amounts of bean meal to observe the effects on female oviposition, percentage of development to adulthood and juvenile development time. These traits were combined in a composite index measuring the alteration of the multiplication rate of C. maculatus fed on artificial seed. The activity of lectin-like extracts was observed on chickpea artificial seed spiked with bean seed extract. Incorporation of bean flour at a rate of 10 and 20% in chickpea artificial seed significantly decreased C. maculatus female fecundity, percentage of adult emergence, and greatly increased the development time. Feeding trials with protein extracts of P. vulgaris reduced fecundity and survival of C. maculatus. Incorporation of 10% V. caracalla bean seed meal in chickpea artificial seed, reduced the multiplication potential of C. maculatus by over 90% showing that bean seed lectin extracts are worthy of further investigation for post-harvest infestation 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 LC₅₀ was respectively 0.48 and 0.54 mg/l for C. maculatus and D. basalis. The ovicidal activity of this compound was high; the LC₅₀ 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.     

Comparison of direct and indirect sampling procedures for Plodia interpunctella in a maize storage facility

Weekly sampling of the Indian meal moth, Plodia interpunctella, was conducted over 15 consecutive weeks at 19 locations within a maize storage facility. Direct sampling consisted of maize samples from two depths from the maize surface, and was compared with three indirect sampling techniques: (1) cardboard traps intended for trapping of late instar larvae and pupae; (2) unbaited sticky traps at two heights above the maize intended for trapping adults; and (3) probe traps inserted into the maize intended for trapping both larvae and adults. Temperature was recorded weekly and maize moisture content every 2 weeks at each sampled location. Total catches for the entire sampling period were highest with cardboard traps followed by maize samples, sticky traps, and probe traps. Spatial statistics were used to examine the distribution pattern of weekly catches for each sampling technique: (1) larvae in both top and bottom maize samples indicated similar aggregated distribution patterns; (2) catches with cardboard traps and sticky traps at both heights suggested a random distribution pattern; and (3) catches with probe traps were considered too low for analysis. For each weekly sampling event, the level of spatial association between sampling techniques was investigated in which the spatial distribution of larvae in top samples was compared with: (1) larvae in bottom maize samples; (2) cardboard trap catches; and (3) adults sticky traps. Catches of adults in low sticky traps were compared with: (4) adults in high sticky traps; (5) cardboard trap catches; and (6) larvae in bottom maize samples. Of the six spatial associations, only larvae in the top and bottom maize samples were significantly associated, while there was no significant spatial association involving catches with indirect sampling techniques. We used response surface regression analysis to evaluate the relative contribution of six explanatory variables in a model fitted to the abundance of larvae in maize samples (order of importance): y-coordinate of sampling locations, vertical position of samples, temperature, number of weekly sampling event, moisture content, and x-coordinate of sampling locations. Using additional response surface regression analyses with the same explanatory variables, we showed that abundance of larvae in maize samples was a poor predictor for the occurrence of P. interpunctella individuals in indirect samples. The implications of different spatial distribution patterns for different sampling techniques of P. interpunctella are discussed.     

DNA identification of two laboratory colonies of the weevils, Sitophilus oryzae (L.) and S. zeamais Motschulsky (Coleoptera: Curculionidae) in Taiwan

DNA amplification fingerprinting (DAF) and nuclear ribosomal DNA (nrDNA) amplification were used to discriminate between two laboratory colonies of two closely related species of weevils: the rice weevil, Sitophilus oryzae (L.), and the maize weevil, S. zeamais Motschulsky. For DAF, three sets of primers (aldolase, prolactin receptor, and interleukin-1β) were used for identification by polymerase chain reaction (PCR) and agarose gel electrophoresis, and the highly similar patterns of the resultant amplicons reconfirmed that the two weevils are closely related. The fragments of nrDNA amplification showed that for S. oryzae and S. zeamais, the homologies of the nucleotide sequences of the internal transcribed spacer regions, ITS-1 and ITS-2, were unusually high, at 96% and 97%, respectively. Based on the ITS-1 and ITS-2 sequences, two species-specific primer sets were designed: with the primer set ITS3/So, the predicted 450 bp DNA fragment was yielded with S. oryzae genomic DNA after PCR amplification (n=10), but no PCR product was obtained with S. zeamais (n=10); with the primer set ITS3/Sz, the same 10 S. zeamais specimens yielded a 550 bp DNA fragment, but S. oryzae yielded no amplicons. In view of the difficulty of distinguishing between these two closely related species, the specificity and availability of these two primer sets might prove to be a useful tool for distinguishing between them. However, the nrDNA sequences of the ITS-1 and ITS-2 regions of geographically isolated populations of both weevils still need to be elucidated, and the applicability of this technique to different geographical populations will need to be confirmed by further study.     

Low and high temperatures for the control of cowpea beetle, callosobruchus maculatus (F.) (coleoptera: Bruchidae) in chickpeas

Chickpea (Cicer arietinum L.; Leguminasae) is an important pulse crop grown, around the world. The whole grain of chickpea is damaged by the cowpea seed beetle, Callosobruchus maculatus (Coleoptera: Bruchidae), which is the most important field-carry-over storage pest of pulses. The management of this insect in storage using chemicals leads to insecticide residues in grains and insecticide resistance development in insects. Thermal disinfestation is one of the means of physical insect control. Eggs, larvae, pupae and adults were held at 42 or 0 °C for varying durations. Pupae and adults were equally heat tolerant. The lethal time to reduce survival by 50% (LT₅₀) at 42 °C for eggs, larvae, pupae and adults were 18, 57, 78 and 71 h, respectively. Pupa was the most cold-tolerant stage. The LT₅₀ at 0 °C for eggs, larvae, pupae and adults were 3, 8, 10 and 4 d, respectively. The LT₅₀ for pupae were 4907, 4262, 336, 36 and 13 min at the grain temperature of 42, 45, 50, 55 and 60 °C, respectively. The LT₅₀ of pupae at 0,−5,−10 and −15 °C were 274, 122, 7 and 2 h, respectively.     

Selection for tolerance to volatile monoterpenoids in Sitophilus oryzae (L.), Rhyzopertha dominica (F.) and Cryptolestes pusillus (Schönherr)

Selection for tolerance to 8 monoterpenoids (linalool, camphor, γ-terpinene, S-carvone, geraniol, estragole, E-anethole, and fenchone) in three pests of stored rice, Sitophilus oryzae, Rhyzopertha dominica and Cryptolestes pusillus, as well as the metabolic mechanisms implicated, was studied. Strains were selected for tolerance towards each monoterpenoid from susceptible insect populations for each of seven generations.After selection, tolerance was observed towards linalool, S-carvone and estragole in S. oryzae and towards camphor in C. pusillus. Populations of R. dominica were not observed to develop tolerance to monoterpenoids.The activity of three enzymatic systems detoxifying these monoterpenoids, microsomal P-450 monooxygenase, esterase, and glutathione S-transferase (GST), were analyzed to study the metabolic mechanisms involved. Esterases could be involved in S. oryzae tolerance whereas P-450 monooxygenases could be involved for most monoterpenoids in selected populations of R. dominica and C. pusillus.     

Augmented release of Teretrius nigrescens Lewis (Coleoptera: Histeridae) for the control of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) in stored cassava chips

A trial was set up in northern Benin to evaluate the potential of Teretrius nigrescens to reduce the infestation and damage to cassava chips caused by storage insects. Cassava chips were stored for 5 months in mud silos and 50 adults of T. nigrescens were added when the stores were first filled. Stores where no predator was released were monitored as controls. The main storage insects observed were Prostephanus truncatus and Dinoderus spp. Initial chip weight varied between 102 and 246 g with no difference between treatments. Chip weight and number of holes on chips initially differed between treatments after 2 months of storage. After 3 months of storage, losses reached 40-50% without T. nigrescens and 30-40% when cassava chips were stored with T. nigrescens. A farmer can increase his profit by 1437 Fcfa/100 kg (1$=560 Fcfa, 1£=968 Fcfa; 1€=656 Fcfa, as on 2 December 2005) through the use of T. nigrescens because losses are reduced by 11%. Data analysis showed that there were significant differences (P<0.0001) between the two treatments for the number of holes, number of insects, weight of each chip as well as damage. There were twice as many P. truncatus and holes on chips in stores where T. nigrescens was not released. The addition of the predator to farmers’ stores is an economic option for controlling losses due to insects in cassava chips.     

Resistance in maize to the Larger Grain Borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

Host plant resistance in maize can be a useful component of Integrated Pest Management (IPM) of the Larger Grain Borer (LGB), Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae). The germplasm bank of the International Maize and Wheat Improvement Centre (CIMMYT) has more than 14,000 maize accessions from all over the world. In 1993, from the seed regeneration nursery of Caribbean land races, 105 land races were selected using good plant type as the criterion. When grains of these land races were infested with LGB in the laboratory, 19 showed resistance as evidenced by the low amount of powder (chewed uneaten maize plus feces) formed 140 days after the infestation. Through a series of infestation, selection and inbreeding (self-pollination of land races) over four generations, S₃ maize ears were generated. These ears showed a high level of resistance as indicated by a low powder production relative to the susceptible control. The LGB reproduction was adversely affected on resistant ears as indicated by the small size of adult populations. Thus, antibiosis could be the mechanism of resistance operating within the S₃ progenies of selected land races. Such sources of resistance can be very useful in developing maize populations/hybrids for use in IPM of LGB.