Susceptibility of Eggs and Adult Fecundity of the Lesser Grain Borer, Rhyzopertha dominca, Exposed to Methoprene

A series of tests were conducted to determine the susceptibility of eggs and neonates of the lesser grain borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae = Bostrychidae), exposed to the insect growth regulator, methoprene, on filter paper and on rough rice. In the first test, the hatch rate of eggs exposed on filter paper treated with methoprene at the label rate of 0.003 mg [AI]/cm2 when used as a surface treatment in structures was 52.0 ± 7.3% compared to 93.0 ± 3.3% on untreated controls. In the second test, eggs were exposed to a dose-response series of 0.00003 to 0.03 mg[AI]/cm2. Egg hatch was directly proportional to concentration and ranged from 85.0 ± 2.0% on untreated controls to 26.7 ± 8.3% at the highest concentration tested. In the third test, 1 ppm of methoprene was sprayed on long grain rough rice (paddy) (Cocodrie variety), and then individual kernels were cracked and an egg of R. dominica was placed directly on the kernel. On untreated rice kernels, 67.5 ± 11.6% of the eggs hatched and were able to bore inside, and all of these larvae emerged as adults. In contrast, 40.0 ± 5.3% of the eggs placed on treated cracked kernels were able to develop to where the larvae were visible through X-ray detection, but none emerged as adults. In the final test, newly-emerged adults were exposed on rough rice treated with 1 ppm methoprene. The number of eggs from adults on untreated rice was 52.1 ± 4.3 eggs per female, and on treated rice the average egg production was 12.5 ± 1.1 eggs per female. Methoprene applied on a surface or on rough rice affected development of egg hatch also reduced fecundity of parent adults exposed on the treated rough rice

Behavioral interactions between Sitophilus zeamais and Tribolium castaneum: the first colonizer matters

There is lack of knowledge on the interactions between kernel aging and the simultaneous infestation by insects, both internal and external feeders. In the present paper, we report results obtained in arena-olfactometer assays in which we studied possible preference and behavioral relationships between the primary colonizer Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) and the secondary colonizer Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). For this purpose, three experiments were conducted. The experiment I examined the response of S. zeamais adults at the fresh or stored kernels damaged by T. castaneum adults, compared to the control and the response of T. castaneum adults at the fresh or stored kernels damaged by S. zeamais adults, compared to the control. The experiment II examined the response of S. zeamais adults at the intact fresh or stored kernels conditioned at different conditioning intervals (1, 7, and 14 days) with kernels damaged by T. castaneum, compared to the control and the response of T. castaneum adults at the intact fresh or stored kernels conditioned at different conditioning intervals (1, 7 and 14 days) with kernels damaged by S. zeamais, compared to the control. The experiment III examined the response of S. zeamais adults at kernels contaminated at different contamination intervals by larvae or adults of T. castaneum, and the response of T. castaneum adults at kernels contaminated by larvae or adults of S. zeamais. In experiment I, significantly more S. zeamais adults were found in traps containing fresh or stored kernels damaged by T. castaneum than in the controls. Significantly more T. castaneum adults were found in traps containing fresh or stored kernels damaged by S. zeamais than in the controls. In experiment II, at 7 days of conditioning, significantly more adults of S. zeamais were captured in the traps used as control than in the traps containing either fresh conditioned kernels or stored conditioned kernels. At 1 and 14 days of conditioning, significantly more adults of T. castaneum were captured in the traps that contained stored conditioned kernels damaged by S. zeamais than in the controls. In experiment III, at 1, 7, and 14 days of contamination, significantly more adults of S. zeamais were captured in traps with kernels contaminated by larvae of T. castaneum or in the traps with kernels contaminated by adult females of T. castaneum than in the controls. Significantly more S. zeamais adults were found in traps containing kernels contaminated by T. castaneum adult males than in control kernels at the 7 and 14 days of contamination. At 1 day of contamination, significantly more adults of T. castaneum were captured in traps with kernels contaminated by larvae of S. zeamais than in the controls. The results of the present study suggest that kernels which were previously infested by S. zeamais were more prone to be selected by T. castaneum adults and kernels that were previously infested by T. castaneum were more prone to be selected by S. zeamais. Thus, the first colonizer can serve as the primary colonizer of stored grains, even if this first colonizer cannot infest sound kernels. The kernel age was also a crucial issue for the attraction of S. zeamais and T. castaneum. Stored kernels exhibited a stronger influence on the attraction of T. castaneum than for S. zeamais