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Title: GRAVIMETRIC METHOD FOR DETERMINING STAGE OF OBLIGATE INTERNALLY FEEDING STORED-PRODUCT INSECTS

Author
item WEAVER, DAVID - MONTANA STATE UNIV
item Opit, George
item MASON, LINDA - PURDUE UNIVERSITY
item Throne, James

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2006
Publication Date: 12/31/2006
Citation: Weaver, D.K., Opit, G.P., Mason, L.J., Throne, J.E. 2006. Gravimetric method for determining stage of obligate internally feeding stored-product insects. Environmental Entomology 35: 1483-1490.

Interpretive Summary: Insects feed on stored grains and can cause extensive losses. The immature stages of the most serious insect pests of stored grains feed inside the kernels, thus making them difficult to see and hampering research on these pests. We developed a method for following development of these insects inside kernels by weighing the kernels twice a day and correcting for weight changes in uninfested kernels caused by changes in abiotic conditions, such as temperature, relative humidity, and barometric pressure. The method accurately indicates when the egg, larval, and pupal molts occur, but not when molts between the individual larval stages occur. The method will be useful for research on the biology and control of these pests of stored grain.

Technical Abstract: We conducted two experiments to develop a gravimetric method for determining the stadia of Callosobruchus maculatus developing in cowpeas. An important step was to develop regression equations for predicting weight changes in uninfested cowpeas in order to correct for changes that occur in weight as a result of changing environmental conditions, such as temperature, relative humidity, and barometric pressure. This was vital because we needed to have a way of determining weight changes in infested peas that were due to the insects developing within them; even the weight of uninfested peas changed over the course of the experiments. The observed weight of each infested pea was corrected based on the proportion weight change in uninfested peas each time weighing was done to get an estimate of the cumulative change in weight due to the presence of the insect. For each infested pea, cumulative change in weight was plotted against time, and plots were analyzed to determine whether a pattern existed that could be used to consistently distinguish stadia. In the second experiment we used an ultrasonic detector to validate results from the gravimetric method. We found that the gravimetric method provided accurate information on duration of the egg, larval, and pupal stages of C. maculatus. However, the gravimetric method could not reliably distinguish the four larval stages of C. maculatus. Our paper also discusses practical applications of the gravimetric method for determining the stadia of internally feeding insects in the context of the current and previous research.