Chemical bases for maize grain resistance to infestation and damage by the maize weevil,Sitophilus zeamais Motschulsky

It was suggested that the factors that confer resistance on a maize variety against Sitophilus zeamais Motschulsky are chemically based. To test this hypothesis, resistance indices of the weevil were assessed using a new scale developed by Nwosu et al. (2015a) after performing detailed chemical analysis of the whole-maize grain using twenty elite maize varieties under ambient temperature and relative humidity of 30.7 °C and 74.5% respectively. Increases in maize varietal crude fibre, phenolic acid and trypsin inhibitor increased significantly mortality of S. zeamais adults and reduced significantly survival rate of S. zeamais adults, percent of grain damage, percent of weight loss, weight of grain flour and oviposition by the adult females. The level of cystein proteinase inhibitor (a natural protectant of plants against insect attack) in the grains was not on its own responsible for increased mortality, reduced grain damage and reduced oviposition. The study identified crude fibre, phenolic acid and trypsin inhibitor of whole-maize grain as the bases for resistance. Their significant increase in grains resulted in low infestation. Whereas, increased protein, zinc, magnesium, calcium, sodium, phosphorus, manganese, iron, cobalt and starch rendered the elite maize grains susceptible to S. zeamais attack. Therefore, significant incorporation of the bases for resistance and significant reduction of the bases for susceptibility in maize grains during breeding programmes is advocated; provided this does not adversely affect palatability and nutritional needs of man. Eighty-five percent of the elite maize varieties were at least resistant to S. zeamais infestation and damage. The resistant varieties, particularly 2000SYNEE-WSTR and TZBRELD3C5 maize with high resistance should be promoted for growing. Antibiosis, antixenosis and preference were the mechanisms of maize grain resistance to S. zeamais attack.     

Development of Sitophilus zeamais Motschulsky,in maize kernels and pellets made from maize kernel fractions

As a means of studying certain aspects of resistance of maize varieties to Sitophilus zeamais, various types of pellets were prepared using ground maize and compared with whole, pericarpless, and germless kernels. Numbers of weevil progeny (from six females and three males, and usually a 7-day oviposition period) were greatest in pellets made of flour moistened with water containing agar. More progeny was produced in pellets than in whole kernels. Damaged kernels (hot-water treated, pericarpless, germless) were more susceptible than undamaged kernels and fewer weevil progeny were produced in pellets made of germless kernels than from pellets of whole kernels. Additions of small amounts of extra germ tissue to whole maize flour enhanced the susceptibility of pellets to the weevil, but adding larger amounts of germ of pericarp reduced progeny number, weight and developmental speed.     

Resistance of maize to the maize weevil: III. Grain weight loss assessment and implications for breeding

The maize weevil (Sitophilus zeamais) is a significant pest of stored maize grain in tropical and subtropical regions worldwide. As a further step towards finding maize genotypes with acceptable levels of resistance to the maize weevil, 53 experimental maize hybrids that were generated in a North Carolina design II mating scheme, were evaluated for grain weight loss due to maize weevil damage under ambient temperature and humidity (ATH) conditions, in the on-station stock room at Harare, Zimbabwe. The study indicated that genotypic variation for grain weevil resistance was large (19%–57%) after five months of infestation by the maize weevils. A few F₂ populations with potential for use as sources of breeding new varieties for maize weevil resistance were identified. They displayed consistency of high performance (better than the standard control varieties) and showed a lower rate of grain weight loss due to the maize weevils over the five months in the stock room. The male and female GCA and SCA effects were highly significant (P ≤ 0.01) for maize weevil resistance, especially at two months after infestation, indicating that resistance was controlled by genes with both additive and non-additive effects, respectively. Further, the distribution of grain weight loss data for the hybrids was continuous and almost normal at the four intervals of data collection, clearly supporting that resistance was partial and possibly conditioned by minor genes with cumulative effects. Therefore, resistance could probably be improved by selection among the promising F₂ populations identified in this study. Although resistance was partial, a plot of grain weight loss of hybrids from the different categories demonstrated the advantage to farmers for growing a resistant variety (low percentage loss over time) compared to the susceptible ones that incurred significant grain weight losses. However, grain weight loss data were not significantly correlated with yield (r = 0.14; P > 0.05), suggesting that the traits are not mutually exclusive. Therefore, breeding for maize weevil resistance in these populations would not necessarily compromise grain yield. Our results demonstrate that there is potential in developing maize varieties with acceptable levels of maize weevil resistance through recurrent selection procedures which exploit both GCA and SCA effects with sustainable impact on food security and the environment.     

Efficacy of filter cake and Triplex powders from Ethiopia applied to wheat against Sitophilus zeamais and Sitophilus oryzae

The efficacy of filter cake and Triplex powders applied to wheat was evaluated in the laboratory against the maize weevil, Sitophilus zeamais Motschulsky and rice weevil, Sitophilus oryzae (Linnaeus)—two most common insect pests associated with stored grain in Ethiopia. Efficacy of these powders was determined by exposing 20 adults of each species to 100 g of wheat treated with 0, 100, 500, 700 and 1000 mg/kg of filter cake and Triplex. Adult mortality was determined 7 and 14 d after exposure. In addition, adult progeny production, percentage of insect damaged kernels, and percentage of grain weight loss at each species-powder-concentration-time combinations were determined after 42 d. The 7 and 14 d mortality was 100% for adults of both species exposed to 1000 mg/kg of filter cake; only the 14 d mortality of Sitophilus species was 100% for adults exposed to 700 mg/kg. Mortality of S. oryzae adults was 100% when exposed for 14 d to1000 mg/kg of Triplex. Mortality of S. zeamais never reached 100% in any Triplex treatments. Adult progeny production of S. zeamais was completely suppressed at filter cake concentrations of 700 and 1000 mg/kg, whereas 1000 mg/kg was necessary for complete suppression of S. oryzae adult progeny production. Complete suppression of adult progeny production was not observed in any Triplex treatments. Complete reduction in percentage of insect damaged kernels and percentage of grain weight loss were obtained when S. zeamais and S. oryzae adults were exposed to 1000 mg/kg of filter cake; similar reductions with S. zeamais occurred only at 1000 mg/kg of Triplex. In the case of S. oryzae, complete reduction of insect damaged kernels and grain weight loss were not achieved at any concentration of Triplex. These powders can be used as alternatives to chemical insecticides for management of Sitophilus species.     

Responses of phosphine susceptible and resistant strains of five stored-product insect species to chlorine dioxide

Adults of phosphine susceptible laboratory strains and phosphine resistant field strains of five stored-product insect species were exposed in vials with 0 or 10 g of wheat for different time periods to 0.54 g/m³ (200 ppm) of chlorine dioxide gas. After exposure, adult mortality was determined 5 d later at 28 °C and 65% r.h. The 5-d mortality was 100% in laboratory and field strains of the red flour beetle, Tribolium castaneum (Herbst); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); lesser grain borer, Rhyzopertha dominica (F.); maize weevil, Sitophilus zeamais Motschulsky; and rice weevil, Sitophilus oryzae (L.) that were exposed in vials with 10 g of wheat to chlorine dioxide for 26, 16, 24–34, 18–24, and 15–18 h, respectively. Corresponding exposure durations for these species and strains in vials without wheat were 15, 3, 18–20, 7–15, and 5–7 h, respectively. Dosages of chlorine dioxide producing 99% mortality (LD₉₉) of T. castaneum, O. surinamensis, R. dominica, S. zeamais, and S. oryzae strains in vials with wheat ranged from 14.79−22.57, 8.20–8.41, 15.79–21.60, 10.66–14.53, and 7.67–12.20 g-h/m³, respectively. In vials without wheat, corresponding LD₉₉ values for T. castaneum, R. dominica, and S. zeamais strains were 6.51–8.66, 11.46–23.17, and 5.79–10.26 g-h/m³, respectively. LD₉₉ values for O. surinamensis and S. oryzae could not be computed, because of 100% mortality after a 3–5 h exposure to chlorine dioxide. No adult progeny production of T. castaneum and O. surinamensis was observed after 8 weeks in control and chlorine dioxide-exposed samples. Adult progeny production of Sitophilus spp. was found only in the control samples. The dosage for 99% adult progeny reduction relative to control for R. dominica strains ranged from 10.07 to 18.11 g-h/m³. Chlorine dioxide gas is effective in killing phosphine susceptible and resistant strains of five stored-product insect species and suppressing adult progeny production of three out of the five species.     

Resistance of selected Mozambican local and improved maize genotypes to maize weevil,Sitophilus zeamais (Motschulsky)

Maize weevil Sitophilus zeamais (Motschulsky) is one of the most important pests of on-farm stored maize in thetropics, particularly where there is no control of moisture content and application of pesticides. This study aimed todetermine the level of resistance among Mozambican maize genotypes against S. zeamais. A total of 17 genotypes,composed of seven experimental hybrids developed from S5 inbred lines from five populations, one released hybrid,two improved open pollinated varieties (OPV), three landraces from Mozambique, two resistant and two susceptiblechecks from Kenya were screened for their resistance to S. zeamais. Four hybrids were screened at their F1 and F2generations. The genotypes were evaluated in the post-harvest laboratory, Kiboko, Kenya in a completely randomizeddesign, replicated 4 times. Data was collected on the number of emerged insects, seed weight loss, seed damage,median development period; and protein, starch and oil contents. The Dobie index of susceptibility was used to groupthe genotypes. Six of the of the eight hybrids at the F1 generation were resistant while two were moderately resistant.Three of the four hybrids evaluated at the F2 generation were moderately resistant while one was susceptible. Two ofthe five OPVs evaluated (EV8430DMRSR and landrace Kandjerendjere) were resistant. Genotypes with high proteincontent showed resistance while those with high starch contents showed susceptibility. Weevils fed on the resistantgenotype produced low number of F1 progeny, had a high median developmental time, caused low seed damage andlow seed weight loss. The resistant genotypes can be either used as cultivars or as sources of resistance in a breedingprogram for weevil resistance.     

Effect of CO2 modified atmosphere packaging on aflatoxin production in maize infested with Sitophilus zeamais

The weevil Sitophilus zeamais (Motschulsky), the maize weevil, is a pest of stored maize that can cause feeding damage and lead to the proliferation of toxigenic fungi. The application of modified atmospheres with a high concentration of CO₂ is an alternative method for the control of S. zeamais and the inhibition of fungal growth. The objectives of the study were to determine the effect of S. zeamais infestation, grain damage and grain moisture content on aflatoxin production by Aspergillus flavus on maize, and the impact of high CO₂ modified atmosphere packaging on pest infestation and aflatoxin production. Mycotoxin production was only recorded when maize was infested with S. zeamais and had A. flavus inoculum. However, production of mycotoxins was not recorded when the maize was mechanically damaged and stored at 18% moisture content, indicating that the biological activity of the insect was determinant in the production of mycotoxins. The high CO₂ modified atmosphere packaging tested (90% CO₂, 5% O₂ and 5% N₂) prevented mycotoxin production.     

Influence of rearing medium on size and weight of adults of four Sitophilus populations and on weight loss of host kernels (Coleoptera: Curculionidae)

Four populations of Sitophilus (S. zeamais Motsch. from Mexico, S. zeamais from Arkansas, U.S.A., S. oryzae (L.) and S. granarius (L.) were studied. Hard red winter wheat (“Cloud” variety), brown commercial sorghum, and yellow and white “dent” maize (mixed varieties) were used to determine the effect of parent-and progeny-rearing media on the adult elytron length in each population. Kernel weight loss caused by individuals of each population and weevil weights were determined.Elytron lengths of S. oryzae progeny were significantly (P < 0.05) but only slightly longer, when parents were reared in wheat rather than sorghum or maize; otherwise parent-rearing medium had no effect. Progeny-rearing medium, not parent size, was most responsible for differences in elytron lengths. S. granarius progeny from wheat were significantly larger than those from maize or sorghum; progeny from all other populations were significantly larger from maize than from wheat or sorghum.S. oryzae caused less weight loss in kernels of wheat and sorghum, and were significantly lighter (P < 0.05) than other insects. The Arkansas S. zeamais was significantly heavier than Mexican S. zeamais in wheat, otherwise their weights were similar. Weight losses (actual and percentages) of kernels of all grains were similar for Arkansas S. zeamais and Mexican S. zeamais. S. granarius were heavier and produced greater weight loss in wheat kernels than other populations did.     

Partial characterization of glutathione S-transferases in pyrethroid-resistant and -susceptible populations of the maize weevil, Sitophilus zeamais

Glutathione S-transferases (GSTs) from a susceptible (Sete Lagoas) and two pyrethroid-resistant populations (Jacarezinho and Juiz de Fora) of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) were characterized through in vitro colorimetric assays. GSTs showed higher activity peaks at pH 9.0 and 30 °C. The K_m-values for GSTs were similar among the populations except for the resistant population from Juiz de Fora, which was about two-fold higher than the susceptible population from Sete Lagoas when using 1-chloro-2,4-dinitrobenzene (CDNB) as substrate (and a fixed concentration of reduced glutathione—GSH). The V_max of this same resistant population was also over two-fold higher than that of the pyrethroid-susceptible population when CDNB and GSH were used as substrates. The resistant population from Jacarezinho also had a slightly, but significantly, higher V_max than the susceptible population when using these two substrates. However, there were no significant differences among the kinetic parameters of GSTs from the maize weevil populations when DCNB and GSH were used as substrates. These results provide evidence of the involvement of enhanced GST activity as an additional pyrethroid-resistant mechanism in at least some maize weevil populations from Brazil.     

Efficacy of Silicosec, filter cake and wood ash against the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) on three maize genotypes

The effectiveness of the diatomaceous earth Silicosec, a mineral industrial filter cake and domestic wood ash, applied at three different rates for the control of the maize weevil, Sitophilus zeamais, on three maize genotypes was determined. Treatment with Silicosec was the most effective followed by filter cake and wood ash. The treatments reduced progeny emergence, percentage grain damage and grain weight losses, but did not affect percentage seed germination. Grain treated with wood ash at all rates resulted in a relatively low mortality 3 days after infestation as compared to other treatments. However, all treatments caused high mortality (97-100%) after 15 days of exposure. Therefore, Silicosec, filter cake and wood ash can be considered as potential components of an integrated pest management strategy against the maize weevil.     

Rolliniastatin-1, a bis-tetrahydrofuran acetogenin: The major compound of Annona mucosa Jacq. (Annonaceae) has potent grain-protective properties

The widespread use of synthetic insecticides results in insecticide-resistant populations of maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae), a primary pest species of stored corn worldwide. Thus, new active ingredients with different modes of action are needed for integrated pest management (IPM) of stored grains. Thus, toxicological bioassays (using S. zeamais as bioindicator) associated to chromatographic techniques were performed to isolate insecticidal compounds from the grain-protective ethanolic extract of Annona mucosa Jacq. (Annonaceae) seeds. The acetogenin bis-tetrahydrofuran rolliniastatin-1 was identified as major bioactive constituent from A. mucosa seeds based on bioassay-guided fractionation, along with rolliniastatin-2, deethylrollinastatin-1, jimenezin and fractions containing triglycerides. This compound produced 51.1% of mortality of adult weevils when applied at 57.66 mg kg⁻¹, drastically reducing F₁ progeny and their damage to corn grains. Although the acute toxicity level was lower than that with the formulation based on diatomaceous earth at a concentration 17.3 times higher (Insecto®^, at recommended rate) used as a positive control, rolliniastatin-1 protected grain statistically similar to that of the positive control. Furthermore, bioassays indicate that compounds of different chemical natures have a synergistic effect on the overall biological activity of seed derivatives of A. mucosa. Efficacy and technical viability of the process to obtain rolliniastatin-1 from the seeds of A. mucosa should allow the production of a botanical insecticide to control populations of S. zeamais at corn warehouses.     

Efficacy of castor bean oil (Ricinus communis L.) against maize weevils (Sitophilus zeamais Mots.) in northwestern Ethiopia

The maize weevil, Sitophilus zeamais Mots. (Coleoptera: Curculionidae), undermines food security. The biocidal activity of castor bean oil (Ricinus communis L.) against S. zeamais, was studied at various doses at Dembecha, northwestern Ethiopia in 2013/14 (November–April). In the castor bean oil efficacy test, weevil mortality steadily increased with castor bean oil dose. According to the results of the ANOVA, number of dead weevils significantly varied between castor bean oil doses 1 h after treatment (F_{10, 21} = 117.6, p < 0.0001). Just 53% of the weevils were killed in one hour by applying 2 ml of the oil while doses higher than 2 ml killed greater than 85% of the weevils. Using Probit analysis, the LD₅₀ of using castor bean oil against maize weevils was calculated to be 2.04 ml. Therefore, 2 ml of castor bean oil was found sufficient to destroy 50% of the weevils. Higher doses of castor bean oil significantly reduced maize seed germination.     

Is flint corn naturally resistant to Sitophilus zeamais infestation?

Sitophilus zeamais (maize weevil) is one of the most destructive pests of maize stored in tropical and subtropical regions. This study determined the resistance of flint corn and dent corn to infestation by S. zeamais (Motschulsky), the maize weevil. Improved King Philip hybrid flint corn and Fontanelle 6T-510 hybrid dent corn were used in this experiment. Two temperature conditions (10 °C and 27 °C) and two storage times (15 days and 30 days) were used. Results showed that flint corn was more resistant to insect damage than dent corn at 27 °C and 30 day storage time. After 30 days storage time and 27 °C death rate was significantly higher in flint corn (R² = 0.945) compared to (R² = 0.634) in dent corn. Damaged seed was 10% higher in dent corn then in flint corn at 27 °C and 30 days. However, no significant difference was observed for seed weight loss between flint corn and dent corn at the same storage conditions. Both dent and flint corn were extensively cultivated in developing countries It appears that storage of flint corn may be one promising solution to reducing corn damage infestation problems in the tropics and in developing countries, but more research is needed.     

Tolerance of Sitophilus zeamais (Coleoptera: Curculionidae) to heated controlled atmosphere treatments

Combination heat and controlled atmosphere (CA) postharvest phytosanitary treatments are environmentally friendly alternatives to chemical fumigants. A controlled atmosphere/heating block system (CA-HBS) was used to rapidly assess tolerances of adult maize weevil, Sitophilus zeamais, both under regular air (RA) and CA (1% O₂ and 15% CO₂) conditions. In the RA treatment, thermal death kinetics for S. zeamais adults were determined at temperatures between 46 °C and 52 °C at a heating rate of 5 °C/min. The results showed that thermal death curves of S. zeamais adults followed a 0th-order kinetic reaction model. The required holding times for achieving 100% mortality were 165, 40, 14, and 4 min at 46, 48, 50 and 52 °C, respectively. The activation energy for killing S. zeamais adults was 526.7 kJ/mol. The effects of CA at various temperature-time combinations and heating rates on insect mortality were evaluated. The mortality of S. zeamais adults was higher under CA treatment than in the heat treatment alone. The slowest heating rate (0.1 °C/min) achieved the highest insect mortality in CA treatments but lowest mortality in RA treatments. The information obtained from the CA-HBS can be used to develop combination heat and CA treatments against S. zeamais.     

Efficacy of combining Niger seed oil with malathion 5% dust formulation on maize against the maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae)

The combined effects of Niger seed oil and malathion, 5% dust, against the maize weevil, Sitophilus zeamais, were evaluated to determine the minimum effective rate(s) of the combinations that can provide adequate protection to maize seed against attack by weevils. Niger seed oil at the rates of 0%, 10%, 20%, 30%, 40%, 50% and 100% of the recommended application rate, 5 ml kg⁻¹, was combined with malathion at the respective rates of 100%, 50%, 40%, 30%, 20%, 10% and 0% of the recommended application rate, 0.5 g kg⁻¹. All combinations provided complete protection to maize seed from the maize weevil up to 90 days after infestation. To determine the residual effects of the treatments, weevils were reintroduced to the grain that had been treated 90 days previously. In addition to 100% malathion, 10% Niger seed oil + 50% malathion, and 20% Niger seed oil + 40% malathion, were fully effective in controlling S. zeamais for a further 156 days after this re-infestation. Therefore, these combinations could be considered as a potential component in an effort to establish integrated management of the maize weevil. Residual performance of both oil and malathion against the weevils was primarily affected by the dose of malathion, with higher doses of malathion providing greater protection for a longer period. Niger seed oil treatment lowered the level of seed germination at the application rate of 5 ml per kg of maize.     

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

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

Evaluation of the insecticidal activity of Moringa oleifera seed extract and lectin (WSMoL) against Sitophilus zeamais

The maize weevil Sitophilus zeamais is a pest of remarkable economic importance as it attacks stored grains, processed cereals, and industrial foods. In this study, a water extract (WE) from Moringa oleifera seeds and water-soluble lectin (WSMoL) isolated from it were investigated for insecticidal activity against S. zeamais adults. The insects were maintained for 10 days on plates containing an artificial diet composed of wheat flour supplemented with WE (60.0–640.0 mg/g) or WSMoL (0.5–60 mg/g). Mortality rate, insect biomass, and amount of food consumed were recorded. The effects of WE and WSMoL on trypsin-like, α-amylase, and endoglucanase activities from insect guts were also investigated. Phytochemical analysis revealed the presence of flavonoids, tannins, saponins, phenylpropanoids, alkaloids, and reducing sugars in the WE. Furthermore, the presence of rutin and ellagic acid was confirmed by HPLC. The extract was toxic to S. zeamais (LC₅₀: 214.6 mg/g) while WSMoL caused slight mortality (12.0 ± 2.7%) at the highest tested dose (60 mg/g). The intake of WE exerted moderate to strong deterrent effects. Moreover, WSMoL decreased the relative biomass gain rate and efficiency in the conversion of ingested food but did not exert deterrent action. The WE stimulated α-amylase and endoglucanase activities, while WSMoL stimulated trypsin-like activity from S. zeamais gut. In conclusion, the WE was toxic to S. zeamais probably due to its feeding-deterrent activity, while WSMoL did not cause acute mortality but negatively affected the nutritional physiology of the insects, which can have long-term impacts.     

Use of plant oils from the southwestern Amazon for the control of maize weevil

The purpose of this study was to evaluate the insecticidal potential of oils obtained from plant species endemic to the southwestern Amazon region against the maize weevil (Sitophilus zeamais Motschulsky). We evaluated the mortality of insects treated with 11 plant oils. After the discriminant assays, concentration–mortality bioassays were conducted to evaluate the toxicity of each oil. The insects were treated with the oils, and mortality was assessed after 24 h. Each assay was performed in four replicates. The LC₅₀ of the oils against S. zeamais ranged between 53.35% and 65.22% for the oils obtained from Astrocaryum aculeatum Meyer, Copaifera spp., Carapa guianensis Aublet, Oenocarpus bataua Mart., Mauritia flexuosa L,. and Orbignya phalerata Mart. These oils exhibited consistency in their toxic activity and emerged as potential alternatives to be implemented in integrated pest management programs for stored product pests. The results of this investigation identified several plant species in the Amazonian flora with potential insecticidal properties.     

Bioactivity of Jatropha curcas L. to insect pests of stored products

The objective of this research was to assess insecticidal activity of seeds and derivatives of Jatropha curcas to insect pests of stored grains. Lethal exposure times were estimated for 50 and 95% (LT₅₀ and LT₉₅) of the adults of Sitophilus zeamais and Rhyzorpertha dominica to seeds of four genotypes of J. curcas: Gonçalo, Paraguaçu, Filomena and Bento. Toxicity of powders and aqueous extracts from seeds and pericarps of J. curcas were tested on S. zeamais, R. dominica, Tribolium castaneum and Oryzaephilus surimanensis. A uniform toxic response was observed among the four genotypes for S. zeamais and R. dominica. The powders and aqueous extracts from seeds and pericarps were lethal to S. zeamais, R. dominica, T. castaneum and O. surimanensis. However, insect mortality was higher in the treatments from seeds, compared to the treatments from pericarps.     

Insecticidal effect of spinetoram against six major stored grain insect species

Spinetoram is a novel insecticide that belongs to the spinosyn class of insecticidal chemicals. The efficacy of spinetoram against numerous insect pest species in a variety of field crops has been well demonstrated. However, there are no data available for the effectiveness of spinetoram against stored grain insects. In the present study, we evaluated spinetoram as a grain protectant, against six stored-product Coleoptera. The species tested were: the rice weevil, Sitophilus oryzae, the lesser grain borer, Rhyzopertha dominica, the larger grain borer, Prostephanus truncatus, the confused flour beetle, Tribolium confusum, the granary weevil, Sitophilus granarius and the sawtoothed grain beetle, Oryzaephilus surinamensis. All species were tested at the adult stage, on wheat (or maize in the case of P. truncatus) treated to achieve spinetoram concentrations of 0.01, 0.1, 0.5, 1, 2, 5 and 10 ppm. Mortality was recorded after 1, 2, 7, 14 and 21 d of exposure, and 65 d later the wheat and maize were examined for offspring emergence. Among the species examined, P. truncatus and R. dominica were by far the most susceptible, given that mortality was close to 100% after 7 d on wheat treated or maize with 0.1 ppm of spinetoram. At this concentration, progeny production of P. truncatus and R. dominica was negligible. On the other hand, T. confusum was the least susceptible; mortality reached 95% only at 10 ppm, and only after 14 d of exposure. Similarly, O. surinamensis was of limited susceptibility to spinetoram; mortality reached 95% only after 14 d of exposure on wheat treated with 5 ppm. Nevertheless, offspring emergence of these species was extremely low. For S. granarius and S. oryzae, complete (100%) mortality was recorded after 14 d of exposure, at 0.5 and 1 ppm, respectively. At these concentrations or higher, progeny production was notably reduced. The results of the present study demonstrate that spinetoram is effective as a grain protectant, but its efficacy varies according to the target species, concentration and exposure interval.