Christos G. Athanassiou

Efficacy of grain protectants against four psocid species on maize, rice and wheat.

BACKGROUND Psocids are emerging pests in stored products, particularly in amylaceous commodities such as grains. Currently, their control is based on the use of fumigants and contact insecticides; however, newer data indicate that psocids are tolerant to insecticides used to control other stored-grain species. This study evaluated the insecticides registered in the USA for use on stored maize, rice and wheat for control of the psocid species Lepinotus reticulatus, Liposcelis entomophila, L. bostrychophila and L. paeta. Mortality of exposed adult females was recorded after 7 and 14 days of exposure, while progeny production was assessed after 30 days of exposure. RESULTS On wheat and rice, chlorpyriphos-methyl + deltamethrin was generally more effective against exposed parental adults than spinosad or pyrethrin, while pirimiphos-methyl was more effective on maize than spinosad or pyrethrin. In most cases, progeny production was suppressed in the treated grains. Progeny production was consistently lowest on wheat and rice treated with chlorpyriphos-methyl + deltamethrin and maize treated with pirimiphos-methyl. CONCLUSIONS Chlorpyriphos-methyl + deltamethrin and pirimiphos-methyl were the most effective insecticides for all species and commodities. Conversely, efficacy of spinosad or pyrethrum was highly dependent on the psocid species and commodity.

Effectiveness of Sulfuryl Fluoride for Control of Different Life Stages of Stored-Product Psocids (Psocoptera)

ABSTRACT With the phase-out and impending ban of methyl bromide, sulfuryl fluoride is among the most promising alternative fumigant insecticides for control of stored-product insect pests. It has been evaluated for control of several stored-product insect pests, but there are few data available on its efficacy for control of stored-product psocids (Psocoptera). We evaluated sulfuryl fluoride for control of different life stages of the psocids Liposcelis paeta Pearman, L. entomophila (Enderlein), L. bostrychophila Badonnel, L. decolor Pearman, and Lepinotus reticulatus Enderlein (Trogiidae) in 48-hr trials at 27.5 °C Adults and nymphs were susceptible to sulfuryl fluoride. Complete (100%) adult and nymphal mortality was recorded at concentrations between 4 and 8 g/m3, except for L. decolor for which all adults were only killed at 24 g/m3. Eggs were tolerant to sulfuryl fluoride. Complete egg mortality was achieved at 24 and 72 g/m3 for L. reticulatus and L. decolor, respectively. Survival of L. paeta eggs was recorded even after exposure to 96 g/m3. Given that the highest United States label concentration for sulfuryl fluoride for a 48-h exposure interval is 31.25 g/m3, our study indicates that high doses and/or longer exposures are needed for complete mortality of eggs of L. decolor and L. paeta. Moreover, the present work suggests that there is considerable variation in efficacy of sulfuryl fluoride for control of different psocid species.

Efficacy of a Combination of Beta-Cyfluthrin and Imidacloprid and Beta-Cyfluthrin Alone for Control of Stored-Product Insects on Concrete

ABSTRACT The insecticidal effect of Temprid, a formulation that contains beta-cyfluthrin and imidacloprid, was tested on concrete for control of seven stored-product insect species: the rusty grain beetle, Cryptolestes ferrugineus (Stephens); the sawtoothed grain beetle, Oryzaephilus surinamensis (L.); the red flour beetle, Tribolium castaneum (Herbst); the confused flour beetle, T. confusum Jacquelin du Val; the hide beetle, Dermestes maculatus (DeGeer); and the psocids Liposcelis bostrychophila Badonnel and L. paeta Pearman. Temprid, which contains 10.5% beta-cyfluthrin and 21% imidacloprid, was tested at the rate of 17.2 ml of formulation/4.1 liters of water/100 m2. Adults were exposed for 4, 8, 14, and 24 h, and then daily for 7 d, on untreated dishes or dishes treated with Temprid. In the untreated dishes, mortality of C. ferrugineus and O. surinamensis was lower when food was present, but food did not affect mortality of the other species. Presence of food did not affect mortality of any of the species tested in the treated dishes. C. ferrugineus, O. surinamensis, and the two psocid species were very susceptible to Temprid, with mortality of 97–100% after 7 d of exposure. In contrast, D. maculatus, T. castaneum, and T. confusum were tolerant to Temprid, as mortality did not exceed 57, 25, and 17%, respectively, at the 7-d exposure. A separate series of similar bioassays with Tempo, a formulation that contains 11.8% beta-cyfluthrin alone, which was applied at the same dose rate as Temprid, was conducted using O. surinamensis and T. castaneum as the target insect species, and results showed that Tempo was at least as effective as Temprid. Our results indicate that the simultaneous use of beta-cyfluthrin with imidacloprid is not more effective on concrete than beta-cyfluthrin alone, and efficacy of both formulations varies with the target species.

Efficacy of layer treatment with methoprene for control of Rhyzopertha dominica (Coleoptera: Bostrychidae) on wheat, rice and maize.

BACKGROUND Insect growth regulators are promising alternatives to traditional pesticides in stored grain. The efficacy of the juvenile hormone analogue methoprene was evaluated as a layer treatment in a laboratory experiment for control of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) in wheat, rice and maize. RESULTS Adults of R. dominica were placed in vials containing 33, 26 and 29 g (to a depth of 6.5 cm) of wheat, rice and maize, respectively, that was entirely or partially treated with 1, 5 or 10 mg kg(-1) methoprene. In wheat and rice, the layer treatments were not as effective as the whole-grain treatment, but there was decreased progeny production as the application rate increased. However, on maize the partial treatments were as effective as the whole-grain treatment at 5 and 10 mg kg(-1) . CONCLUSIONS The results suggest that partial layer treatments with methoprene can be used to control R. dominica on maize but may not be effective for control of this species on wheat and rice.

Residual Efficacy of Chlorfenapyr for Control of Stored-Product Psocids (Psocoptera)

ABSTRACT The residual effect of chlorfenapyr (Phantom) was evaluated for residual control of three stored-product psocid species: Liposcelis bostrychophila Badonnel, Liposcelis entomophila (Enderlein), and Liposcelis paeta Pearman (Psocoptera: Liposcelididae). Chlorfenapyr was applied to individual arenas with a concrete surface at rates of 0, 2.8, 13.8, 20.6, 27.5, 55, and 110 mg active ingredient (AI)/m2. Adults were exposed on the treated arenas and mortality assessed after 1, 2, and 3 d. The procedures were repeated weekly on the same treated arenas for 3 wk to assess residual efficacy. At each week, mortality of all species was low after 1 d of exposure but notably increased after 2 or 3 d. L. entomophila was the most susceptible species, with 99–100% mortality at rates of 13.8 mg/ m2 or higher. Similarly, mortality of L. paeta after 3 d of exposure at the same concentration ranged from 92 to 100%. L. bostrychophila was the least susceptible species, with mortality of <60% during the third week after application at rates ≤27.5 mg/m2. However, even for this species, mortality after 3 wk was 90% or higher at rates >27.5 mg/m2. Complete mortality of all species occurred after 3 d exposure at the highest rate tested of 110 mg/m2. Thus, our results show that chlorfenapyr is effective against major psocid species at the application rates evaluated in this study.

Efficacy of Deltamethrin Against Stored-Product Beetles at Short Exposure Intervals or on a Partially Treated Rice Mass

ABSTRACT Stored-product insects can potentially be exposed to grain protectants for variable time periods. Adults of three species, the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae), and the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) were exposed for 1, 4, 8, and 24 h on brown rice treated with the pyrethroid deltamethrin at the label rate of 0.5 ppm, then removed and placed on untreated rice. Adults of these same species plus the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), and the warehouse beetle, Trogoderma variabile Ballion (Coleoptera: Dermestidae) were exposed on treated brown rice mixed with varying amounts of untreated rice to assess progeny production. Immediate and delayed mortality of exposed adults did not exceed 7% for any exposure interval, but progeny production for T. castaneum was generally lower in comparison with that for the other species. Increasing the amount of treated rice decreased progeny production of R. dominica but not for any Sitophilus species. Mixed results were obtained for T. castaneum and T. variabile. Results show that long exposure times and treatment of an entire rice mass may be necessary to give complete control of stored-product beetles.

Competition among Species of Stored-Product Psocids (Psocoptera) in Stored Grain

We evaluated the competition among stored-product psocid species by conducting two series of laboratory experiments. In the first series, three species of Liposcelididae were used: Liposcelis bostrychophila, Liposcelis decolor, and Liposcelis paeta. Five adult females of these species were placed in vials containing wheat, either alone or in all possible combinations of two species. The number of adults in the vials was counted after 35, 70, 105, 140, and 175 days. These tests were performed at 25 and 30°C. At 25°C, there were no differences in numbers of L. bostrychophila when this species was reared either alone or with each of the other two species. At 30°C, L. bostrychophila was the dominant species. The presence of L. bostrychophila had a negative effect on the growth of populations of L. decolor and L. paeta. The presence of L. paeta did not affect growth of populations of L. decolor, although the presence of L. decolor occasionally reduced growth of populations of L. paeta. In the second series of tests, L. bostrychophila adult females were placed in vials of wheat either alone or with adult females of Lepinotus reticulatus, at the ratios of (L. bostrychophila: L. reticulatus) 10∶0, 9∶1, 7∶3, 5∶5, 3∶7, 1∶9, and 0∶10. These tests were carried out only at 30°C, and the observation periods were the same as for the first series of tests. Liposcelis bostrychophila was the dominant species in this case as well, regardless of the ratio of the parental females. At the end of the experimental period, L. reticulatus was present only in vials that contained this species alone. Our results showed that L. bostrychophila outcompetes the other stored-product psocid species tested.

Efficacy of Methyl Bromide for Control of Different Life Stages of Stored-Product Psocids

ABSTRACT The psocid species Liposcelis paeta Pearman, Liposcelis entomophila (Enderlein), Liposcelis decolor (Pearman), Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae), and Lepinotus reticulatus Enderlein (Psocoptera: Trogiidae) were evaluated in laboratory bioassays to determine their susceptibility to six concentrations of methyl bromide (0.027, 0.113, 0.280, 0.393, 0.452, and 0.616 g/m3) after 48 h of exposure at 27.5°C. The life stages that were evaluated were adults (for all species), nymphs (for all species except Lep. reticulatus), and eggs (for L. entomophila, L. decolor, and L. bostrychophila). Adults and nymphs were very susceptible, and complete mortality was recorded at concentrations between 0.027 and 0.280 g/m3. In contrast, eggs were by far more tolerant than adults and nymphs for all species tested. At 0.027 g/m3, mortality did not exceed 53%, while survival was high even at 0.113 g/m3. Complete (100%) egg mortality was recorded at 0.393 g/m3 for L. decolor and at 0.452 g/m3 for L. entomophila and L. bostrychophila; concentrations estimated to give 99% mortality for eggs of these three species were 0.710, 1.044, and 0.891 g/m3, respectively. These results show that stored-product psocids are susceptible to methyl bromide, but concentrations of ≥0.452 g/m3 should be used to control all life stages.

Susceptibility of Different Life Stages of Tribolium confusum (Coleoptera: Tenebrionidae) and Oryzaephilus surinamensis (Coleoptera: Silvanidae) to Cold Treatment

Laboratory tests were carried out to examine the efficacy of different exposure intervals (2 h, 4 h, 8 h, 1 d, 2 d, 3 d, and 7 d) on different life stages (adults, pupae, larvae, and eggs) of Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), the confused flour beetle, and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), the saw-toothed grain beetle (adults, larvae, and eggs) to 0, -5, -10, and -15°C. Larvae and pupae of T. confusum were more cold-tolerant than eggs or adults. Exposure to temperatures of -10°C for 1 d will kill nearly 100% of all life stages of T. confusum. O. surinamensis was more cold-tolerant than T. confusum. Adults of O. surinamensis were not killed when exposed for 1 d at -5°C, but egg hatch was drastically reduced after 2 h of exposure at the same temperature. Eggs and adults of O. surinamensis were more cold-tolerant than larvae. Our study indicates that target insect species and life stage, temperature, and exposure interval should all be considered when cold treatment is selected as a control strategy against T. confusum and O. surinamensis. Facility managers can use these data in planning cold treatments.

Effect of the Presence of Live or Dead Insects on Subsequent Captures of Six Stored-Product Beetle Species: The Relative Species Matters

Abstract In trapping programs prior capture of individuals of the same or different species may influence subsequent attractiveness of the trap. To evaluate this process with stored-product insects, the effect of the presence of dead or alive adults in traps on the behavioral responses of six stored-product insect species, Tribolium confusum Jacquelin du Val, T. castaneum (Herbst) (Coleoptera: Tenebrionidae), Sitophilus oryzae (L.), S. granarius (L.) (Coleoptera: Curculionidae), Oryzaephilus surinamensis (L.) and O. mercator (Fauvel) (Coleoptera: Silvanidae), was studied in choice tests under laboratory conditions. Two series of tests were carried out. In the first series, the choice was between either alive or dead adults of same species and blank (no adults). Overall, dead adults had the strongest influence, increasing the response of S. oryzae, S. granarius, O. surinamensis, and O. mercator and decreasing the response of the two Tribolium species. Presence of alive adults generally did not result in a response different from blank, except for T. castaneum and O. surinamensis that had a reduced response. In the second series of tests, the choice was between alive or dead individuals of the species vs. alive or dead individuals of its relative cogeneric species. For choices between alive individuals, S. oryzae, S. granarius, and O. surinamensis showed a preference for alive individuals of the same species vs. the cogeneric species, and for all the other species there was no preference. For choices between dead individuals, T. castaneum exhibited a preference for individuals of the same species, while S. oryzae, S. granarius, and O. mercator showed a preference for individuals of the cogeneric species, and all other combinations did exhibit a preference. Our results suggest that traps containing alive and dead individuals of the same and other species can seriously affect the response and capture of additional insects.