Efficacy of alpha-cypermethrin and thiamethoxam against Trogoderma granarium Everts (Coleoptera: Dermestidae) and Tenebrio molitor L. (Coleoptera: Tenebrionidae) on concrete

Laboratory bioassays were conducted to evaluate alpha-cypermethrin and thiamethoxam for the control of adults, small larvae and large larvae of the khapra beetle Trogoderma granarium, and the yellow mealworm beetle Tenebrio molitor, on concrete. Factors such as dose (0.025 and 0.1 mg alpha-cypermethrin or thiamethoxam/cm²), exposure interval (1, 3 and 7 d), and formulation (alpha-cypermethrin SC and thiamethoxam WG) were evaluated. Apart from immediate assessment at end of exposure, an assessment of delayed mortality was performed with the survivors of the 7-d exposure by removing them from the treated substrate and keeping them on untreated surfaces for 7 more days. After the 7-d exposure, more T. granarium adults were dead on dishes treated with alpha-cypermethrin than with thiamethoxam. Small larvae were generally less susceptible than adults. After 7 d, small larval mortality reached 64.4% for alpha-cypermethrin, while for thiamethoxam it was <6%. Large T. granarium larvae were more tolerant than the small ones. Delayed mortality of T. granarium adults was generally high for both insecticides and doses, and ranged between 43.3 and 63.3% of those that were still alive immediately after the 7-d treatment. For both larval categories, delayed mortality was higher for larvae that had been previously exposed to alpha-cypermethrin, than with thiamethoxam. For T. molitor, after the 7-d exposure, significantly more adults were dead on dishes treated with alpha-cypermethrin than with thiamethoxam. For small larvae mortality was 38.9% at the lowest thiamethoxam dose, but in the other cases ranged between 88.9 and 95.6%. In the case of large larvae, the overall mortality was low in all tested combinations. Regarding delayed mortality of this species, it remained at low levels, for both adults and small larvae. Our results indicate that T. molitor was more susceptible than T. granarium in both insecticides tested, but alpha-cypermethrin was more effective than thiamethoxam.     

Efficacy of alpha-cypermethrin,chlorfenapyr and pirimiphos-methyl applied on polypropylene bags for the control of Prostephanus truncatus (Horn), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.)

We examined the immediate and delayed mortality of adults of the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae), the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on surfaces of polypropylene storage bags under different treatment scenarios with alpha-cypermethrin, chlorfenapyr and pirimiphos-methyl. These scenarios were: only one surface of the bag was sprayed and insects were exposed on sprayed or unsprayed surface or both surfaces were sprayed. We evaluated the immediate mortality for 1, 3 and 5 days (d) of exposure. Then, we transferred the surviving adults to untreated surfaces of the same type of storage bags and measured the delayed mortality after 7 d of exposure. We also evaluated the effect of insecticidal treatments on the numbers of holes/bites made by the activity of P. truncatus and R. dominica on storage bags. In terms of immediate mortality, chlorfenapyr and pirimiphos-methyl were very effective against all three species and alpha-cypermethrin against P. truncatus. We noticed high mortality values of all species to chlorfenapyr and pirimiphos-methyl, even after 3 d of exposure, reaching 100% in many of the cases examined. For the majority of exposure intervals, insecticides and insects, we did not find significant differences in mortality counts between exposures on sprayed surfaces of the bag. Immediate mortalities of insects exposed on the untreated surface of the bag did not differ significantly with mortalities at the surface single treated with alpha-cypermethrin and pirimiphos-methyl. Concerning delayed mortality, all S. oryzae adults were found dead 7 d after their transfer to untreated bags irrespectively of the treatment. The delayed mortality of P. truncatus and R. dominica adults was either complete (after exposure to chlorfenapyr) or almost complete (after exposure to alpha-cypermethrin). The exposure of P. truncatus and R. dominica to alpha-cypermethrin almost completely suppressed the numbers of holes/bites. Our study indicates that the application of insecticides on polypropylene storage bags can be considered as an effective method for the control of stored-product insects.     

Efficacy of d-tetramethrin and acetamiprid for control of Trogoderma granarium Everts (Coleoptera: Dermestidae) adults and larvae on concrete

The khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) is a dangerous insect of stored products that has currently expanded in Africa, Asia and Europe. Control of this species encounters difficulties when synthetic insecticides are applied either as surface treatments or as grain protectants. Therefore, new insecticidal formulations should be assessed as additional tools towards an effective management of T. granarium. In the current study, we tested the new insecticidal formulation Dobol, that contains the pyrethroid insecticide d-tetramethrin and the neonicotinoid insecticide acetamiprid, as treatments on concrete. Their direct and delayed mortality against adults and larvae of T. granarium were estimated under two label doses (min and max) and two temperature levels (30 and 35 °C) after 1, 2, 3, 4 and 7 d of exposure interval. Results revealed that Dobol caused direct mortality to T. granarium adults that ranged between 87.8 and 96.7%. Concerning larvae, direct mortality was generally much lower, being at most 84.4% at the max dose after 7 d of exposure. Temperature had significant impact on the direct mortality of T. granarium adults and larvae within the vast majority of the tested exposure intervals at both doses. However, when the surviving adults and larvae were transferred on untreated concrete surfaces, despite higher mortality at 35 than 30 °C, there was no significant impact of temperature on their mortalities within any exposure interval and dose. Our study revealed that Dobol is a promising insecticidal formulation that can be effectively used against adults and larvae of T. granarium on concrete surfaces.     

Immediate and delayed effects of short exposures to phosphine on adults and larvae of the khapra beetle,Trogoderma granarium

Adults and larvae of the khapra beetle, Trogoderma granarium Everts were exposed to 3000 ppm of phosphine through the Phosphine Tolerance Test. In a first series of bioassays, observations were taken every 2 min and the exposed individuals were classified either as walking normally or as being immobilized (knocked down), i.e., not walking normally. In the second series of bioassays all individuals were exposed for 90 min to phosphine. For both bioassays delayed mortality was noted after a 7 and 14-day post exposure interval. Larvae were found to be more tolerant than adults, as the time required for the individuals to be immobilized was up to 20 min, which was almost twice as long as the time required for the immobilization of the adults. There were high levels of adult mortality 7 days later, and complete (100%) mortality 14 days after the exposure. In contrast, larval mortality was low, for both post-exposures. Adults were 100% immobilized after the termination of the 90-min exposure interval at 3000 ppm of phosphine, while the percentage of the active larvae was extremely low. Regarding the 7 days post exposure interval the percentage of larval immobilization was higher than that of adults, but this was reversed seven days later. Interestingly, development of the larvae was delayed compared to the control, after the 90 min exposure, in contrast to 20 min exposure which did not cause any delayed effect. Our work provides some first data for the evaluation of the influence of short exposures to phosphine on adults and larvae of T. granarium, which may be very useful in creating an effective initial quantification plan for the control of this species.     

Efficacy of Beauveria bassiana in combination with an electrostatically charged dust for the control of major stored-product beetle species on concrete

Laboratory bioassays were carried out to determine the insecticidal efficacy of a Beauveria bassiana formulation (Bb38, Exosect Ltd, UK), which is based on the combined use of the fungus with the electrostatically charged dust Entostat. The efficacy of Bb38 was conducted on concrete surfaces against adults of the lesser grain borer, Rhyzopertha dominica, the rice weevil, Sitophilus oryzae, the confused flour beetle, Tribolium confusum and the rusty grain beetle, Cryptolestes ferrugineus, in two series of bioassays. In the first series, adults of the above species were exposed on concrete surfaces treated with Bb38 and mortality was recorded after 7 and 14 days of exposure (immediate mortality). These tests were carried out in all combinations of two temperatures, i.e. 25 and 30° C and two levels of relative humidity (r.h.), i.e. 55 and 75%. In the second series of bioassays, adults of the above species were exposed to Bb38 for 7 days, and after this interval, the surviving individuals were transferred in untreated concrete, where mortality was recorded again 7 and 14 days later (delayed mortality). From the species tested, R. dominica was by far the most susceptible, given that mortality reached 100% in almost all temperatures and r.h. levels. From the other species, S. oryzae and C. ferrugineus were moderately susceptible, while Bb38 was less effective for T. confusum. In the second series, immediate mortality for R. dominica was much higher than that of the other species. Moreover, delayed mortality of R. dominica reached 100% in contrast with the other species, where delayed mortality was low. Based on the results of the present work, we found that the insecticidal effect of Bb38 is not affected much by temperature and r.h., for the vast majority of the species and conditions tested. Moreover, in some cases, there was some post-exposure delayed activity of the formulation. This is one of the few studies that examine commercial formulations of fungal-based insecticides against stored product insects, which are expected to provide solutions in stored product protection, where traditional insecticides cannot be applied, as in the case of organic products.     

Insecticidal effect of contact insecticides against stored product beetle populations with different susceptibility to phosphine

In the present work we evaluated the effect of alpha-cypermethrin, pirimiphos-methyl and spinetoram on field and laboratory strains of Sitophilus oryzae (L.) and Oryzaephilus surinamensis (L.) with different susceptibility levels to phosphine. The field populations were collected from storage facilities in Greece and were characterized as resistant by using the Food and Agriculture Organization (FAO) protocol, based on the same protocol, populations were characterized as susceptible to phosphine. The insecticides were applied at three dose rates (0.1, 1 and 10 ppm) on wheat and adult mortality was measured after 7, 14 and 21 days of exposure, while progeny production was assessed 65 days later. For S. oryzae populations, complete control was noted at the highest dose on pirimiphos-methyl and spinetoram, while mortality caused by alpha-cypermethrin was 62 and 100% for the field and laboratory populations, respectively. For O. surinamensis, complete control was recorded at the highest dose only on alpha-cypermethrin for the laboratory population, in contrast with the field population, where mortality was only 32% after 21 days of exposure. In general, the variations among populations were negligible for spinetoram, probably due to the fact that the populations tested were not previously exposed to this active ingredient. In contrast, the lowest susceptibility of the field populations to the other two insecticides can be attributed to the fact that these populations might have been exposed to these active ingredients, while any hypothesis for cross-resistance with phosphine has to be examined more thoroughly.     

Susceptibility of Trogoderma granarium Everts and Trogoderma inclusum LeConte (Coleoptera: Dermestidae) to residual contact insecticides

Commercial formulations of the pyrethroid insecticides β-cyfluthrin and deltamethrin were evaluated for delayed mortality of Trogoderma granarium (Everts), the khapra beetle, and T. inclusum (LeConte), the larger cabinet beetle. Ten 3-4 week-old larvae of either species were exposed on treated concrete arenas for 1, 2, 3, and 7 d then transferred into 175 ml diet cups containing 5 g of untreated rearing media for 30 d to evaluate delayed mortality. In a subsequent study, residual efficacy of β-cyfluthrin, deltamethrin, and chlorfenapyr was evaluated at 0–12 wks post-treatment against adults and larvae of a laboratory and a field strain of T. granarium. Ten adults or larvae of either strain were exposed on treated arenas at selected wks post-treatment and mortality was assessed after 4 and 30 d of exposure for adults and larvae, respectively. In the first study, delayed morality of T. granarium and T. inclusum larvae was <26% when exposed on arenas treated with the two pyrethroids, and T. inclusum larvae were less susceptible than T. granarium. Adult mortality was 90–100% for both strains of T. granarium across post-treatment assays regardless of insecticide treatment and there was no difference between strains. All three insecticides produced 100% mortality for the laboratory strain of T. granarium larvae in initial post-treatment assays, but then efficacy declined. Field strain larvae were more tolerant to the insecticides than laboratory strain larvae, and larvae of both T. granarium strains were more tolerant than adults. Longer exposure times were required to produce complete mortality of larvae compared to adults. All three insecticides provided residual efficacy of adults for up to three months.     

The efficacy of different surface applications of wettable powder formulation of Detech® diatomaceous earth against the rice weevil,Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

In this study, the insecticidal activity of the wettable powder formulation of Detech® diatomaceous earth against the rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae), an important stored grain pest, was investigated. Detech® diatomaceous earth was applied on concrete and wooden surfaces at doses of 0.25, 0.5, 1 and 2 g/m² and the mortality of S. oryzae adults was observed at time intervals of 24, 48, 72, 96, 120, 144, 168, 192, 216, 240, 264 and 288 h. In the first 24 h of application on the concrete and wooden surfaces, no death was observed. At the 48^th hour, no effect or very low mortality was observed on the concrete and wooden surface at all doses. While the increase in dose and exposure time on the concrete and wooden surface increased the mortality rate of the adults, complete adult mortality was obtained on concrete surfaces after 288 h. The wettable powder formulation of Detech® diatomaceous earth at a dose of 2 g/m² is highly effective against rice weevils on wood and concrete surfaces at laboratory conditions, though with greater success on concrete, but the longer DE exposures increase the efficacy on both surfaces.     

Effect of thiamethoxam partial grain treatment to Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) adults

The efficacy of partial treatment of two commodities (wheat and rice) with thiamethoxam against adults of Rhyzopertha dominica (F.) and Sitophilus oryzae (F.) was tested by mixing different proportions of thiamethoxam-treated and untreated grains. Thiamethoxam was applied to these grains in two different doses 1 and 5 ppm, while the percentage of the treated grain quantity ranged between 0 and 100%. Adult mortality was recorded after time exposure intervals of 7 and 14 d. Irrespectively of the dose, adult mortality was raised with increase in the percentage of treated kernels as well as the exposure time. Applications of thiamethoxam on wheat were more effective than on rice and on R. dominica than on S. oryzae, especially at 1 ppm, for both exposure intervals. The effective “critical” percentage, causing control similar to 100% treatment, of thiamethoxam to grain mass at 5 ppm was 50% for both species. For the examined scenario of partial treatment, thiamethoxam found to be effective against the tested species which makes it a candidate for use in the stored grain protection.     

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.     

Insecticidal potential of a synthetic zeolite against the cowpea weevil,Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae)

The insecticidal potential of a synthetic zeolite was evaluated against the cowpea weevil, Callosobruchus maculatus (Fabricius). The synthetic zeolite was applied to concrete surfaces at 0, 2.5, 5, 10 and 20 g/m², and the mortality of adults was assessed after 1, 3, 6, 9, 12, 24, 36, 48, and 72 h at 28 °C and 65% r.h. The residual efficacy of zeolite applied at 5 g/m² was evaluated on concrete surfaces at 0, 1, 2, 3, and 4 months post-treatment. Adults of C. maculatus were exposed to cowpeas treated with zeolite at 0, 0.1, 0.5, 1, 2, 3, 4, and 5 g/kg. The number of eggs deposited on cowpea kernels and their hatchability were determined after 7 and 14 d, respectively. The cumulative adult mortality was recorded after 1, 2, 3, and 4 d, and adult progeny production after 42 d. The residual efficacy of zeolite on cowpeas was tested at 0, 1, 2 and 3 months after treatment. On concrete, zeolite applied at ≥ 5 g/m² resulted in 100% mortality of C. maculatus adults after 24–72 h of exposure. Zeolite at 5 g/m² exhibited high residual efficacy with 100% mortality of C. maculatus adults after 36 h exposure on treated surfaces for up to 4 months. The mortality of C. maculatus adults exposed to zeolite-treated cowpeas increased with increasing concentration and exposure time. The number of eggs laid by C. maculatus, number of kernels with eggs, and adult progeny production decreased with increasing zeolite concentration. Zeolite applied to cowpeas at 1 g/kg produced 100, 99 and 77% adult mortality at 1, 2, and 3 months post-treatment. Progeny production on zeolite-treated cowpeas was significantly lower than that on untreated cowpeas. These results show that the synthetic zeolite is effective on concrete surfaces and on cowpeas in controlling C. maculatus.     

Residual toxicity of a commercial cypermethrin formulation on grains against four major storage beetles

In the present study, we investigated the residual insecticidal efficacy of a commercial cypermethrin formulation applied on grains (wheat, maize) against adults of Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.) and Prostephanus truncatus (Horn) in laboratory bioassays. The insecticide was applied in its label dose on the grains and a bioassay was initiated at the day of application and every month for four consecutive months (5 bioassays in total). In each bioassay, adult mortality levels were determined after exposure for 7, 14 and 21 d. After the final evaluation, all beetles (dead and alive) were removed and the number of offspring was assessed after an additional interval of 65 d. Based on our results, the application of the tested cypermethrin formulation as a grain protectant provided long-term protection against R. dominica and P. truncatus adults, as in most cases complete control was achieved for these two species, even after four months of storage of the treated commodities. In the case of S. oryzae and O. surinamensis, adult mortality did not reach 100% in any of the cases, moreover, a gradual decline of mortality levels was recorded over the 4-month period of storage. Finally, for S. oryzae and P. truncatus progeny production was notably suppressed by cypermethrin. Results show that the cypermethrin formulation tested could be a valuable tool for stored grain protection, however, factors such as the target species and the storage interval should be taken into consideration.     

Efficacy of the furanosesquiterpene isofuranodiene against the stored-product insects Prostephanus truncatus (Coleoptera: Bostrychidae) and Trogoderma granarium (Coleoptera: Dermestidae)

In plant and animal kingdoms, isofuranodiene is a widespread, lipophilic and volatile furanosesquiterpene endowed with insecticidal properties. In the current study, we evaluated its toxicity against the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae) adults and the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) adults and larvae at 500 and 1000 ppm. Results showed that the overall mortality of P. truncatus adults exposed to 500 ppm was low, while at the higher dose tested it increased to 56.7% after 7 days of exposure. Notably, isofuranodiene killed 95.6 and 96.7% of the exposed T. granarium adults 5 and 7 days post-exposure at 1000 ppm. On the other side, T. granarium larval mortality did not exceed 24.4 and 37.8% at 500 and 1000 ppm respectively, after 7 days of exposure. Isofuranodiene could be considered further to develop novel green tools against T. granarium adults, since there is a lack of effective grain protectants against this noxious species.     

Effectiveness of insecticide-incorporated bags to control stored-product beetles

Adults of seven stored-product beetle species were exposed on the inside and outside surfaces of polypropylene polymer bags incorporated with the insecticide deltamethrin (approx. concentration of 3000 ppm; ZeroFly^® Storage Bags (3 g/kg). Beetles were exposed for 60, 120, and 180 min, and 1, 3 and 5 days on the same treatment arenas, and after the 5 d interval the insects were removed and placed in untreated arenas for 5 more days. All Trogoderma variable (Ballion), the warehouse beetle, Prostephanus truncatus (Horn), the larger grain borer, Rhyzopertha dominica (F.), the lesser grain borer, and Tribolium castaneum (Herbst), the red flour beetle, were knocked down on the outside and inside surfaces of the bag after one hour of exposure. Mortality of T. variable, P. truncatus, and R. dominica increased during the exposure period, with generally lower mortality on the inside versus the outside of the bag after either 3 or 5 days of continual exposure. However, maximum mortality of T. castaneum, the red flour beetle, was only 5.6 ± 3.4% after 5 days of exposure. While it took longer for 100% knockdown of Sitophilus oryzae (L.), the rice weevil, compared to the above species, all S. oryzae were dead after 5 d of exposure on both surfaces. In contrast, after 5 days knockdown of Sitophilus zeamais (Motschlulsky), the maize weevil, did not exceed 30% and there was no mortality. After the Sitophilus species were transferred to untreated arenas, knockdown of all species decreased and mortality increased, indicating delayed mortality and no recovery from knockdown. Mortality of Dermestes maculatus (DeGeer), the hide beetle, did not exceed 5.6% at any time and there was no delayed mortality, indicating a potential tolerance of this particular strain of D. maculatus used in the study. Our results show that the ZeroFly^® Storage Bags could effectively limit penetration of stored-product beetles through the bag into stored grains or milled grain products.     

Evaluation of Carifend® for the control of stored-product beetles

In the present study, the effectiveness of Carifend® (BASF AG, Ludwigshafen, Germany), an alpha-cypermethrin-coated net, was evaluated in laboratory tests against major stored-product insects. The insecticide-treated net was adjusted at the bottom of plastic petri dishes, and adult insects were placed in each dish and exposed for different exposure intervals (1, 3, 5, 7 and 14 days), after which mortality and knockdown was measured. The tests were carried out against a wide spectrum of stored-product insects, i.e. Sitophilus oryzae, Sitophilus granarius, Sitophilus zeamais, Oryzaephilus surinamensis, Tribolium castaneum, Tribolium confusum, Prostephanus truncatus, Rhyzopertha dominica and Cryptolestes ferrugineus. The results showed that O. surinamensis, R. dominica and P. truncatus were highly susceptible to Carifend®, as complete control was achieved for all three species, after 5, 14 and 5 days, respectively. Regarding Sitophilus species, S. zeamais was the most tolerant species, as mortality levels did not exceed 46%, even after 14 days of exposure. In contrast, S. oryzae and S. granarius mortality was >98% after 14 days of exposure. So far, Carifend® has been registered in many parts of the world for the protection of stored tobacco against major tobacco pests, i.e. Lasioderma serricorne and Ephestia elutella. However, our results clearly indicate that this net can be used effectively for the control of other stored-product insects that infest durable food, such as grains and related amylaceous commodities.     

Potential of three enhanced diatomaceous earths against Sitophilus zeamais Motschulsky and Prostephanus truncantus (Horn) on stored maize grain

Global health and environmental concerns against synthetic pesticides in stored-grain coupled with high cost, unavailability and inaccessibility of modern non-chemical grain treatment technologies in Africa are driving the need for low-cost and low-dose combination of readily available alternatives. Laboratory studies were conducted to determine the efficacy of non-registered low-dose food grade diatomaceous earths enhanced with natural grain protectants: IBS at 50, 75 and 100 ppm; IPE1 at 200, 300 and 400 ppm; IPE2 at 100, 150 and 200 ppm against Prostephanus truncatus and Sitophilus zeamais adult insects on maize. Adult insect mortality was assessed at 7, 14 and 21 days after treatment (DAT) while progeny emergence was assessed at 49 and 70 DAT for S. zeamais and P. truncatus, respectively. IBS caused significant (p < 0.05) P. truncatus and S. zeamais adult mortality at 14 and 21 DAT, respectively. Except for IPE1 at 400ppm, lower doses of IPE1 and IPE2 showed significantly low adult mortality (p < 0.05) (54-74%) on Sitophilus zeamais compared to IBS and the positive control. All rates of IPE1 and IPE2 were also not effective on P. truncatus adults, with significantly low mortality (p < 0.05) (18–38% compared to positive control). IBS at 75 and 100 ppm were effective on progeny suppression on both S. zeamais and P. truncatus but IPE1 at 400 ppm was effective on S. zeamais only. These results suggest the potential of IBS and IPE1 (at 400 ppm) as effective sustainable alternatives to synthetic grain protectants for small-scale farmers in sub-Saharan Africa who may not afford the modern non-chemical grain protection technologies. Field efficacy of these materials under typical farmer conditions is required.     

Delayed mortality responses of Rhyzopertha dominica (F.) adults subjected to short exposures on spinosad-treated wheat

Laboratory studies were conducted to characterize post-exposure (delayed) mortality responses of adults of the lesser grain borer, Rhyzopertha dominica (F.), following brief exposures to wheat treated with dry and liquid spinosad formulations at the labeled rate of 1 mg (a.i.) kg⁻¹ of grain. Exposure of R. dominica adults to a dry spinosad formulation at the labeled rate for 4 h resulted in 16–34% mortality. When these adults were placed on untreated wheat, post-exposure mortality continued to increase in a non-linear fashion, with 100% mortality observed at 60 h. Similarly, when R. dominica adults were exposed to wheat treated with a liquid spinosad formulation at the labeled rate for 0.5–48 h, 100% post-exposure mortality on untreated wheat occurred within 24–168 h. Exposure for 72 h resulted in 100% mortality on spinosad-treated wheat itself. There was an inverse relationship between exposure of adults to spinosad-treated wheat and time to 100% mortality on untreated wheat. These results suggested that short exposures (0.5–48 h) of R. dominica adults to wheat treated with the labeled rate of spinosad will ensure its complete control even after removal from treated grain. Adults of R. dominica which disperse to untreated grain after brief exposures to spinosad-treated wheat may eventually die because of delayed toxicity effects of spinosad against this economically important insect species.     

Efficacy of five insecticides for the control of Trogoderma granarium Everts (Coleoptera: Dermestidae) larvae on concrete

Small and large larvae of the khapra beetle, Trogoderma granarium Everts were exposed for 1, 3, and 7 d on concrete that was treated with chlorfenapyr at 0.055 mg active ingredient (a.i.)/cm² and 0.11 mg (a.i.)/cm², deltamethrin at 0.0025 mg (a.i.)/cm² and 0.005 mg (a.i.)/cm², pirimiphos-methyl at 0.025 mg (a.i.)/cm² and 0.05 mg (a.i.)/cm², pyriproxyfen at 0.000115 mg (a.i.)/cm² and 0.00023 mg (a.i.)/cm², and spinosad at 0.05 mg (a.i.)/cm² and 0.1 mg (a.i.)/cm². Then, the survived individuals were transferred on untreated concrete for 7 more days and the delayed mortality of small or large larvae was evaluated. Concerning the immediate mortality of small larvae, chlorfenapyr was the most effective among the insecticides tested causing 70% immediate mortality after 7 d of exposure at the higher dose. The other insecticides provided similar mortality levels with the exception of pyriproxyfen which was not effective, for any of the combinations tested, as mortality did not exceed 4.4%. Delayed mortality for chlorfenapyr was also high reaching 76% at 7 d of exposure at the higher dose. Pirimiphos-methyl and deltamethrin gave similar results, indicating that for these two insecticides there is also a noticeable delayed effect. For pyriproxifen and spinosad, the delayed mortality was low. Large larvae were by far more tolerant than small ones in all dose-insecticide-exposure combinations examined for both immediate and delayed mortality counts. The results of the present study show that none of the insecticides were able to totally control T. granarium larvae, illustrating the difficulties in controlling this species, with dose rates that are usually effective for other major stored product beetle species.     

Efficacy of contact insecticides for the control of the lesser mealworm,Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae)

The lesser mealworm, Alphitobius diaperinus is a common pest of poultry farming facilities, the presence of which harbors diseases and economic loss, but it also occurs in different types of storage and processing facilities, such as feed mills. In this study, we evaluated the efficacy of three contact insecticides, alpha cypermethrin, spinosad, and pirimiphos methyl, against adults and larvae of A. diaperinus in a series of two bioassays. In the first series of bioassays, mortality rates were determined after 1, 3, 7 and 14 days of exposure on concrete dishes treated with the above insecticides. The results show that all three insecticides were effective for the control of this species, since after 14 days of exposure mortality exceeded 90% for both adults and larvae. Spinosad had a definite advantage over the other two insecticides, providing complete (100%) insect mortality after 14 days of exposure. In the second series of bioassays, the presence of food was evaluated to determine the effects of immediate and delayed mortality. We found that the presence of food in the concrete dishes decreased the levels of delayed mortality of the exposed individuals. All three insecticides showed an increased level of delayed mortality, either with or without food, but mortality did not reach 100% for any of the combinations tested. These results present a valid series of data for creating a standardized means of control against this pest that has beset poultry facilities for years.     

Insecticidal efficacy of a binary combination of cyphenothrin and prallethrin,applied as surface treatment against four major stored-product insects

In the present study, we investigated the insecticidal efficacy of a commercial binary combination of two pyrethroids, cyphenothrin and prallethrin, as structural treatment against adults of Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), Tribolium confusum Jacquelin du Val and Prostephanus truncatus (Horn) in laboratory bioassays. In a first series of bioassays, the insecticide was applied at its label dose on concrete and metal surfaces, whereas mortality and knockdown levels were recorded after 1, 3, 7 and 14 d of exposure. In a second series of bioassays, the residual efficacy of the insecticide was evaluated on concrete for a period of four months, stored either in continuous darkness or exposed to light. In these bioassays, mortality and knockdown of the exposed insects was measured after 3, 7 and 14 d of exposure. Finally, in a third series of bioassays, we investigated the immediate and delayed effect of the tested formulation on adults of the four insect species after exposure for 1, 3 and 7 d. Based on our results, the application of the tested insecticide as surface treatment can provide efficient control against adults of all four species tested. The surface type did not significantly affect the insecticidal efficacy of the tested formulation, at least for the surfaces tested. Moreover, exposure to light negatively affected the residual activity of the insecticide, as for all insect species tested, mortality was significantly lower on dishes exposed to light than on the ones stored in the dark for storage intervals equal or longer than two months. Finally, reduced delayed mortality was observed for all exposure intervals, as knocked down individuals remained, in most cases, knocked down even 7 d after their removal from the treated dishes.