Monday, December 10, 2007 - 10:17 AM

Imidacloprid and spider mite fecundity: Is there a connection?

Adrianna Szczepaniec, and Michael J. Raupp, University of Maryland, Dept. of Entomology, 4112 Plant Sciences Bldg, College Park, MD

Benefits of imidacloprid, a systemic neonicotinoid insecticide, have been offset by reports of secondary mite outbreaks on treated plants. One of the hypothesis erected to explain these outbreaks is hormoligosis, which is defined as increased fitness of an organism exposed to sublethal levels of a stress agent. In reported cases of hormoligosis, increases in fecundity have been the most frequently evaluated estimate of fitness. Previous studies linking spider mite fecundity and imidacloprid applications produced ambiguous results. In this study, we examined the reproductive response of boxwood spider mites, Eutetranychus buxi, elm spider mites, Tetranychus schoeni, and two-spotted spider mites, Tetranychus urticae, to imidacloprid. Excised branches or leaves of boxwoods and elms, and intact leaves of tomatoes were used in experiments. Daily fecundity of female spider mites of known age was recorded until their death. Results of experiments indicate a higher fecundity of females exposed to imidacloprid in plant tissues in all 3 plant systems. Fecundity of spider mites consuming treated plants increased by an average of 30%. We did not find any significant differences in longevity between the two treatments although there was a trend for mites to live longer when fed leaves treated with imidacloprid.

Species 1: Acari Tetranychidae Eutetranychus buxi (boxwood spider mite)
Species 2: Acari Tetranychidae Tetranychus urticae (two-spotted spider mite)
Species 3: Acari Tetranychidae Tetranychus schoeni