Contribution to the morphology and ecology of Sitophilus zeamais Motsch. in Yugoslavia

After we established the existence of Sitophilus zeamais in Yugoslavia in 1968, we examined the various morphological characters given in the literature in which this species differs from S. oryzae. In an experiment S. zeamais has infested maize in the field, but was unable to survive the winter in the field in Zagreb in any stage of development. It is quite possible that some might survive some winters in the warmer southern parts of the country. When each species was placed separately on samples of wheat, more progeny were obtained from S. zeamais than from S. oryzae. Sitophilus zeamais is more resistant to starvation than S. oryzae. Differences in the suitability of individual maize hybrids for the development of S. zeamais were found. Differences in preference for individual maize hybrids and wheat for oviposition have been determined.     

Toxic and antifeedant action of nutmeg oil against Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch

The essential oil extracted from nutmeg seeds using steam distillation was tested against the stored product insect pests, Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch., for contact toxicity, fumigant toxicity and antifeedant activity. Filter paper impregnation was employed for contact and fumigant toxicity studies, whereas a flour disc bioassay was used to investigate antifeedant effects. Adults of S. zeamais were about ten times more susceptible than T. castaneum adults to contact action (LC₅₀ values of 1.7 mg/cm² and 18 mg/cm² respectively). However, S. zeamais adults were only 1.7 times more susceptible than T. castaneum adults to fumigant action (LC₅₀ values of 4.5 mg/cm² and 7.7 mg/cm² respectively). Furthermore, the larvae (10–16 days old) of T. castaneum were more susceptible than the adults, but the susceptibility of the larvae decreased with age. Nutmeg oil also significantly (P < 0.05) affected the hatching of T. castaneum eggs and the subsequent survival of the larvae in the concentration range 1.4–3.2 mg/cm². The production of F1 progeny of both T. castaneum and S. zeamais exposed to media treated with nutmeg oil was significantly (P < 0.05) reduced at all concentrations tested. F1 progeny production was totally suppressed at nutmeg oil concentrations of 1.05 g/100 g rice for T. castaneum and 0.35 g/100 g wheat for S. zeamais. Nutritional studies showed that nutmeg oil significantly (P < 0.05) affected the growth rate and food consumption of both insect species, depending on the concentrations used, but the antifeedant activity was more pronounced against S. zeamaisthan against T. castaneum. At 20 g nutmeg oil/100 ml, the feeding deterrence index of T. castaneum was only about 7%, whereas that of S. zeamaiswas 33%. These results suggest that nutmeg oil may be useful as a grain protectant with contact, fumigant and antifeedant activities against these insects.     

Bioactivity of the essential oil extracted from Evodia rutaecarpa Hook f. et Thomas against the grain storage insects, Sitophilus zeamais Motsch. and Tribolium castaneum (Herbst)

The toxic, repellent and feeding deterrent activities of the essential oil extracted from Evodia rutaecarpa Hook f. et Thomas, were evaluated against Sitophilus zeamais adults and Tribolium castaneum larvae and adults. Contact toxicity assayed by topical application showed that S. zeamais adults were significantly more susceptible (LD₅₀=0.043 μg/mg body wt) to the essential oil than T. castaneum adults (LD₅₀=0.118 μg/mg body wt) and larvae (LD₅₀=0.093–0.126 μg/mg body wt). However, in the fumigation assays, S. zeamais (LC₅₀=41 μg/L air) was less susceptible to the essential oil than T. castaneum (LC₅₀=11.7 μg/L air). When compared with larvae of various ages, T. castaneum adults were more susceptible to the fumigant toxicity of the essential oil. Also, in the treated filter paper repellency test, the essential oil was more repellent to T. castaneum than to S. zeamais. A flour disk bioassay demonstrated that the essential oil of E. rutaecarpa had a weaker feeding deterrent action against T. castaneum adults than against T. castaneum larvae and S. zeamais adults. The reduction in growth rate of T. castaneum larvae and S. zeamais adults was mainly due to a behavioural (feeding deterrent) action rather than to post-ingestive toxicity of the oil.     

Insecticidal properties of eugenol, isoeugenol and methyleugenol and their effects on nutrition of Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Eugenol, isoeugenol and methyleugenol showed similar contact toxicity to Sitophilus zeamais (LD₅₀ values approximately 30 μg/mg insect). For Tribolium castaneum, the order of potency of these chemicals compared by the LD₅₀ level was isoeugenol>eugenol>methyleugenol. Furthermore, S. zeamais was generally more susceptible than T. castaneum to these three compounds except for isoeugenol based on the LD₅₀ level. When sublethal doses (doses that produce no appreciable mortality) of eugenol, isoeugenol and methyleugenol were topically applied to adults of either species of beetles pre-treated with deltamethrin, the toxicity of deltamethrin was enhanced. A flour disc bioassay using no-choice tests was employed to assess, in terms of food consumption and growth rate, the susceptibility of S. zeamais and T. castaneum to media treated with eugenol, isoeugenol, and methyleugenol. Only eugenol significantly (P<0.05) reduced food consumption (RCR) in the adults of S. zeamais at a concentration of 13.2 mg/g food. However, it reduced the growth rate (RGR), food consumption and food utilisation (ECI) in adults and larvae of T. castaneum at concentrations of 35 and 99 mg/g food, respectively. Isoeugenol reduced the RGR and RCR in S. zeamais adults and T. castaneum adults and larvae, in a concentration-dependent manner, but only reduced ECI in the adults of T. castaneum at the concentration of 76 mg/g food. In comparison, methyleugenol reduced the RGR and RCR in the three groups of insects, and the ECI of S. zeamais adults and T. castaneum larvae.     

Desiccation increases the efficacy of Beauveria bassiana for stored-grain pest insect control

The effect of desiccation stress on the efficacy of Beauveria bassiana for controlling stored-product insects was investigated in laboratory bioassays. The mortality of B. bassiana-treated Plodia interpunctella larvae was greater at a vapor pressure deficit (VPD) of 2.42 or 1.87 kPa than at 1.06 kPa. Moisture also had significant effects on the mortalities of adult rice weevils, Sitophilus oryzae and maize weevils, Sitophilus zeamais. Mortality of S. zeamais was higher at 2.42 and 1.87 kPa than at 1.06 kPa, while mortality of S. oryzae was higher at 1.87 kPa than at either 2.42 or 1.06 kPa. Higher control mortality at the higher two VPDs indicated that S. zeamais was less desiccation tolerant than S. oryzae. The mortalities of B. bassiana-treated adult Cryptolestes ferrugineus, larval Lasioderma serricorne and larval Oryzaephilus surinamensis were not significantly affected by VPD. These results demonstrate that dry stored-grain conditions are favorable for B. bassiana efficacy.     

Susceptibility of stored-product beetles on wheat and maize treated with thiamethoxam: effects of concentration, exposure interval, and temperature

Sitophilus zeamais Motschulsky, the maize weevil, Oryzaephilus surinamensis (L.), the saw-toothed grain beetle, and Tribolium castaneum (Herbst), the red flour beetle, were exposed for 1, 2, 3, and 6 d at 22°C, 27°C, and 32°C on maize treated with 0, 0.5, 1.0, 2.0, or 4.0 ppm thiamethoxam, a new-generation neonicotenoid insecticide. A second series of tests was conducted on hard winter wheat using S. oryzae (L.), the rice weevil, Rhyzopertha dominica (F.), the lesser grain borer, and T. castaneum. Mortality of all species on both commodities generally increased with insecticide concentration, exposure interval, and temperature, and data were described by linear and non-linear regressions with concentration as the independent variable. Mortality of S. zeamais ranged from 58% to 90% on maize treated with 0.5 ppm thiamethoxam, and approached 95–100% as concentration increased to 4 ppm. Oryzaephilus surinamensis appeared to be slightly less susceptible than S. zeamais; mortality ranged from about 18% to 80% at 5 ppm and there was a more gradual increase in mortality as concentration increased. Mortality of T. castaneum generally did not exceed 40% at any concentration unless the beetles were exposed for 6 d. Mortality of R. dominica and S. oryzae was less than 60% when exposed on treated wheat for 1 and 2 d, but increased to nearly 100% when exposed for 6 d at 27°C and 32°C. Mortality of T. castaneum did not exceed 20% at the 1- and 2-d exposures, and approached 100% only when beetles were exposed for 6 d at 32°C. Few F₁ adults of any species were found in treated maize or in treated wheat but the number of F₁ T. castaneum in untreated maize and untreated wheat was very low compared with the other species. Results show that thiamethoxam would be an effective protectant of stored maize seed and stored wheat seed.     

Susceptibility of the gelatinized wheat product bulgur to Sitophilus zeamais Motsch. and Rhyzopertha dominica (F.)

The development of Sitophilus zeamais and Rhyzopertha dominica was studied at relative humidities of 71, 58 and 43% in bulgur and wheat. Male and female adult weevils, introduced into 6 bulgur and 6 wheat media of different particle sizes, were allowed to oviposit for 7 days. Thirty R. dominica eggs were placed in each replicate of a similar set of bulgur and wheat media.

S. zeamais produced more adult progeny in whole kernels of bulgur and of wheat and in the larger-sized particles, and a high percentage of R. dominica larvae developed into adults in these media. S. zeamais progeny produced and R. dominica larvae surviving were fewer, and developmental periods for both species longer, the smaller the particles and the lower the relative humidity. Males and females collected from bulgur and wheat media of the same particle size tended to weigh the same; but the smaller the particle size, the less the weights.     

Field monitoring Sitophilus zeamais and Sitophilus oryzae (Coleoptera: Curculionidae) using refuge and flight traps baited with synthetic pheromone and cracked wheat

Flight traps with open vertical baffles and refuge traps in the form of rectangular cardboard boxes were used to catch Sitophilus zeamais and S. oryzae in Kenya. Traps baited with the aggregation pheromone (Sitophilure), and for the first time traps baited with pheromone and food bait (cracked wheat), were field tested. Both traps types were effective in capturing Sitophilus spp and gave higher weevil catch when baited with pheromone and cracked wheat combined than with pheromone or cracked wheat alone. The combination of pheromone and cracked wheat had an additive effect on trap catch and not a synergistic effect as reported in earlier laboratory trials. Different pheromone loadings of 0.5, 1 and 2 mg were tested. The catch of S. zeamais in flight traps rose significantly with increasing dosage. For refuge traps, the same effect was observed although the difference between 1 mg and 2 mg was not statistically significant. The trend was for increasing S. oryzae catch with dosage, although total catches were very much lower than those for S. zeamais, and differences did not prove statistically significant. Traps placed on the floor near infested maize cribs captured significantly more Sitophilus spp than those actually placed in the cribs. Adult Sitophilus captured were sexed and in both flight and refuge traps the sex ratio was biased in favour of females even though the sex ratio of weevils from infested maize cobs, which were the source of the captured weevils, was approximately even.     

Distribution of and association between the larger grain borer Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) and the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in maize stores

Interspecific interactions between the larger grain borer Prostephanus truncatus and the maize weevil Sitophilus zeamais were studied during two storage seasons in maize stores, in Bénin. Maize ears, randomly sampled from farmers’ grain stores, were ‘reared out’, i.e., kept for 4 weeks under controlled conditions for F₁ to emerge, and periodically sampled, in order to examine colonisation patterns of P. truncatus and S. zeamais. For both storage seasons, P. truncatus and S. zeamais populations were sparsely aggregated and not associated with each other. The degree and strength of association increased with each monthly sampling occasion with the Ochiai, Jaccard and Dice indices of association. By the fourth sampling occasion, P. truncatus was found on most ears and on some ears in very high numbers (>300 insects). Almost all ears with P. truncatus contained at least a few S. zeamais individuals, but many ears with S. zeamais contained no P. truncatus.     

Quality of stored corn (maize) as influenced by Sitophilus zeamais Motsch. and several management practices

The impact of several simulated management practices (malathion treatment, temperature, moisture content, hybrid, and surface disinfection) for Sitophilus zeamais Motsch. on the quality (biochemical composition) and germination of corn (maize) was studied. Quality was evaluated on the basis of protein, ash, lipid, and total nonstructural carbohydrates content, weight loss, and germination.

When the abiotio conditions were favorable for S. zeamais oviposition, larval development, and progeny emergence, the ash, lipid, and protein content of the kernels was increased, as was kernel weight loss. Germination and dry matter were significantly decreased when progeny were present.

The differences in nutritional parameters observed here were generally very small, although highly statistically significant. It is not clear whether these differences are biologically significant, although we feel that they indicate meaningful changes that may occur in corn nutrition and quality following infestation by S. zeamais for several generations.     

Cooking oils and “Triplex” in the control of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in farm-stored maize

The uses of some cooking oils viz., noug oil, soybean oil, sunflower oil, corn oil and olive oil, and the reputedly non-toxic botanical “Triplex”, were evaluated against maize weevil, Sitophilus zeamais, in stored maize grain under local Ethiopian storage conditions in 2003. For comparison, an untreated sample and the synthetic insecticides, malathion 5% dust and Actellic 2% dust, at the recommended rates of 0.05% (w/w) were included. All the cooking oils tested had a significant toxic effect on the weevils in stored grains. The oil treatments showed significantly higher mortality of adult weevils at each sampling period compared with the untreated grains. The cooking oil treatments also significantly reduced weight loss and grain damage as compared with the untreated control. The Triplex treatment was of comparable effectiveness to the synthetic insecticides, causing high mortality of adult weevils, low-percentage grain damage and low-percentage weight losses. These promising oils and Triplex could be recommended for use as part of an integrated pest management program in stored maize, particularly at low levels of pest infestation and, in the case of cooking oils, for grain intended for home consumption.     

Laboratory studies on predation by Teretriosoma nigrescens Lewis (Col.: Histeridae) on Prostephanus truncatus (Horn) (Col.: Bostrichidae) infesting maize cobs in the presence of other maize pests

Over 14 weeks at 27°C, 70% r.h., the mean rate of increase of three pairs of Prostephanus truncatus (Horn) was reduced by a factor of ten or four by the addition, after 3 or 6 weeks respectively, of four adult Teretriosoma nigrescens Lewis. The effect of the predator on Tribolium castaneum (Herbst) and Sitophilus zeamais Motschulsky populations was not as great: the mean rate of increase ofT. castaneum was approximately halved; and S. zeamais was not affected by the presence of the predator. T. castaneum had no significant effect on the numbers of P. truncatus or the numbers and predatory ability of T. nigrescens. Selective predation of P. truncatus by T. nigrescens did not encourage significant increases in populations of S. zeamais or T. castaneum.     

Laboratory evaluation of some additional organophosphorus insecticides against stored-product beetles

The relative susceptibilities of Tribolium confusum Duv. and T. castaneum (Hbst) to seven new organophosphorus insecticides were determined by applying the compounds topically at four dosage rates. SD 8447 (0,0-dimethyl 2-chloro-1-(2,4,5-trichlorophenyl, vinyl phosphate) was more effective than malathion against both species and was evaluated against eight more species of stored-product beetles. It was more toxic than malathion to Rhyzopertha dominica (F.), Lasioderma serricorne (F.), Stegobium paniceum (L.) and Sitophilus zeamais Motsch. but less so against Oryzaephilus surinamensis (L.), O. mercator (Fauv.), Ptinus tectus Boield and Sitophilus granarius (L.). S. zeamais was about eleven times more susceptible to this compound than S. granarius.     

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.     

Evaluation of different temperature management strategies for suppression of Sitophilus zeamais (Motschulsky) in stored maize

Three years of experimental trials (2001–2003) were conducted in 12.7 t capacity pilot-scale bins to determine the survival, reproduction and suppression ofSitophilus zeamais Motschulsky under three temperature management strategies, no aeration (NA, control), ambient aeration (AA, 23.9 °C), and chilled aeration (CA, 18.3 °C) from May to November in Indiana, USA. One-way ANOVA indicated that the number of progeny for small adult populations of caged insects (0.14–0.28 insects per gram maize) embedded 0.6 m deep in the stored grain mass varied among temperature strategies for some, but not all of the storage periods. Progeny numbers in the CA strategy were significantly lower (P<0.05) than those for the NA and AA strategies for periods with longer hours of grain temperature 15.0 °C. There were no differences in progeny numbers between the NA and AA strategies for most of the storage periods. This may have been due to higher mortality, lower oviposition and fecundity from overcrowding of S. zeamais under the NA strategy caused by factors in the caged insect microclimate (e.g., rapid food depletion, heating, moisture, molding, and high CO₂ levels). Our results suggest that maintaining stored maize at temperatures 15.0 °C for longer periods suppressed S. zeamais progeny more effectively than at 18.3 °C. In addition, leaving the stored grain bulk unaerated early in the spring so it remained cool at 15.0 °C due to winter aeration resulted in early suppression of S. zeamais progeny.     

Insect pests associated with rural maize stores in Mexico with particular reference to Prostephanus truncatus (Coleoptera: bostrichidae)

A survey was carried out into the occurrence of insect pests infesting rural stores in five regions of Mexico. Stores were sampled using pheromone-baited crevice traps, bait-bags and maize samples every 28 d for an entire storage season. Maize and store temperatures, and grain moisture content were measured. The most numerous primary pests were Sitophilus zeamais Motsch., Sitotroga cerealella (Olivier) and Prostephanus truncatus (Horn). P. truncatus was more abundant in stores in the drier, temperature regions of Guanajuato, La Laguna and Jalisco than in the more tropical regions, Veracruz or Chiapas. In La Laguna (and to some extent in Jalisco), many more P. truncatus were detected in the store using the crevice trap than were counted in the maize samples, perhaps because crevice traps may attract beetles from outside the store. La Laguna and Chiapas had significantly fewer larvae of P. truncatus in the samples than other regions, probably a result of the lower grain moisture content. Grain damage levels were very low in La Laguna and they occurred later in Guanajuato than elsewhere. The three pest species causing most damage were S. zeamais, S. cerealella and P. truncatus. It is suggested that P. truncatus was important in causing damage primarily in Guanajuato, whereas S. zeamais and S. cerealella caused more damage elsewhere, particularly in more humid areas.     

Ability of naturally occurring parasitoids to suppress the introduced pest Prostephanus truncatus (Horn) (Coleoptera, Bostrichidae) in traditional maize stores in Togo

Beneficial parasitoids associated with traditional maize stores in southern Togo were collected during three storage seasons (1988–1990) at different sites to investigate their relationship to the introduced pest, Prostephanus truncatus. Two parasitoids, Anisopteromalus calandrae and Theocolax elegans were observed regularly and in higher numbers in the samples and were therefore studied for their relationship with P. truncatus. Correlation analysis of population densities observed in stores showed that correlation coefficients for numbers of both parasitoids and P. truncatus were mainly negative and very close to zero, but positive and greater in value for the parasitoids and Sitophilus zeamais. Glass jar trials were carried out with A. calandrae and T. elegans on loose maize. A. calandrae reduced numbers of P. truncatus by 70.1% in the single species culture after 8 weeks, whereas T. elegans had no impact. In double species culture A. calandrae had an effect on both populations; P. truncatus was reduced by 61.3% and S. zeamais by 22.5%. T. elegans only had an influence on S. zeamais.     

The ability of powders and slurries from ten plant species to protect stored grain from attack by Prostephanus truncatus horn (Coleoptera: Bostrichidae) and Sitophilus oryzae L. (Coleoptera: Curculionidae)

Powders and slurries prepared from parts of 10 different plant species indigenous to Ghana were tested under laboratory conditions for their ability to protect stored grain from damage by Sitophilus oryzae L. and Prostephanus truncatus Horn on wheat and maize, respectively. Two concentration levels 10% and 1% (wt/wt) were used. Powders and slurries of all plant species of 10% (wt/wt) significantly (P < 0.001) reduced insect damage by the grains and caused mortality of both insect species. Powders of four species; Cissampelos owariensis, Azadirachta indica, Ricinus communis and Solanum nigrum, gave a significant (P < 0.001) reduction in grain damage by the insect species as well as high mortality, even at the lower concentration level of 1% (wt/wt). The slurry preparations were generally better protectants than the powders especially against S. oryzae where complete control was achieved except with Chromolaena odorata and Sida acuta, which permitted some survival. The pattern of action of the slurries against P. truncatus was similar to that of S. oryzae, except that P. truncatus was relatively more tolerant.     

Toxicity of naturally occurring compounds of Lamiaceae and Lauraceae to three stored-product insects

The compounds 1,8-cineole, camphor, eugenol, linalool, carvacrol, thymol, borneol, bornyl acetate and linalyl acetate occur naturally in the essential oils of the aromatic plants Lavandula angustifolia, Rosmarinus officinalis, Thymus vulgaris and Laurus nobilis. These compounds were evaluated for fumigant activity against adults of Sitophilus oryzae, Rhyzopertha dominica and Tribolium castaneum. The insecticidal activities varied with insect species, compound and the exposure time. The most sensitive species was S. oryzae, followed by Rhyzopertha dominica. Tribolium castaneum was highly tolerant of the tested compounds. 1,8-Cineole, borneol and thymol were highly effective against S. oryzae when applied for 24 h at the lowest dose (0.1 μl/720 ml volume). For Rhyzopertha dominica camphor and linalool were highly effective and produced 100% mortality in the same conditions. Against Tribolium castaneum no oil compounds achieved more than 20% mortality after exposure for 24 h, even with the highest dose (100 μl/720 ml volume). However, after 7 days exposure 1,8-cineole produced 92.5% mortality, followed by camphor (77.5%) and linalool (70.0%). These compounds may be suitable as fumigants because of their high volatility, effectiveness, and their safety.