Submitted to: Journal of Stored Products Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/2001
Publication Date: 2/2/2002
Citation: ARTHUR, F.H. SURVIVAL OF SITOPHILUS ORYZAE(L.) ON WHEAT TREATED WITH DIATOMACEOUS EARTH: IMPACT OF BIOLOGICAL AND ENVIRONMENTAL PARAMETERS ON PRODUCT EFFICACY. JOURNAL OF STORED PRODUCTS RESEARCH 38: 305-313. 2002. Interpretive Summary: The rice weevil is a major internal insect pest of stored wheat. The larvae develop inside the wheat kernel, and insecticides should kill the female weevil before she can deposit eggs. Several experiments were conducted by exposing different numbers of adult weevils on wheat treated with diatomaceous earth, a natural reduced-risk low toxicity insecticide, and held at different temperature and relative humidity combinations. Diatomaceous earth became less effective as relative humidity increased, and higher application rates were necessary to kill rice weevils and prevent progeny production. Increases in temperature led to decreased survival of rice weevils exposed on treated wheat, but these exposed adults were still able to lay eggs so that more offspring were produced at higher temperatures. Diatomaceous earth was relatively stable on stored wheat, but there was a slight loss in effectiveness with time. Reducing both the temperature and moisture content of stored wheat could lead to either reduced application rates of diatomaceous earth required to control rice weevils or an increase in the time that wheat could be safely stored after treatment.
Technical Abstract: Experiments were conducted to evaluate the effects of temperature, relative humidity (RH), population density, concentration, exposure interval, and residual aging on susceptibility of Sitophilus oryzae (L.), the rice weevil, to diatomaceous earth (DE). In the first experiment, hard red winter wheat was treated with 300 ppm of the Protect-It formulation of DE, and different densities of 1-2 week-old mixed-sex adult weevils were exposed for one week on treated wheat held at different temperature, humidity combinations. No weevils survived when exposed at 40 or 57% RH, but at 75% RH survival was related to both population density and temperature. A higher percentage of adults survived when 30 were exposed compared to 10 and 20, and within each density, survival decreased with increasing temperature. No F1s were produced at any RH on wheat held at 22 C, and at 27 and 32 C, the maximum number of F1s were produced on wheat held at 75%RH. In the second experiment, wheat was treated with different concentrations of diatomaceous earth, and 10 mixed sex adult S. oryzae were exposed on treated wheat for 1, 2, or 3 weeks at 27 C and 57 and 75% RH. Survival increased with exposure interval and concentration, but within exposure interval and concentration, survival was usually greater at 75 versus 57% RH. In the final experiment, wheat was treated with 300 ppm, held at 22 and 27 C and 57% RH, and bioassayed at monthly intervals for 3 months by exposing 10 adult mixed-sex S. oryzae on treated wheat for 1 or 2 weeks. At each month, survival of S. oryzae was greater when exposed at 22 compared to 27 C and when exposed for 1 week compared with 2 weeks. Survival gradually increased with each monthly bioassay, except for those conducted at 3 months.