Wednesday, August 8, 2007

PS 55-206: Effects of natural enemies on Geocoris population dynamics in cotton fields

Yao-Hua Law, University of California, Davis

The generalist predator Geocoris (Hemiptera) is a key natural enemy in many agro-ecosystems in California yet much of its ecology remains unknown. Surveys of Geocoris and their prey abundance in cotton fields revealed two unexpected observations: i) Geocoris population dynamics did not match prey availability, and ii) when Geocoris eggs numbers increased, a corresponding recruitment of nymphs and adults was not observed. Several factors might explain these observations: i) intraguild predation on Geocoris by intraguild predators (IGP), e.g. Nabis and Zelus, ii) Geocoris egg-parasitism by a scelionid wasp, Telenomus reynoldsi Gordh and Coker, iii) infection by fungal pathogen, e.g. Beauvaria, and iv) infection by soil entomopathogenic nematodes (EPN). A combination of field experiments and surveys were conducted to test for the roles of these factors. The effects of parasitoids and IGP on Geocoris population dynamics were investigated using caged cotton plants. Surveys of cotton field Geocoris populations were done to check for relative significance of EPN and fungal pathogen infection. The results are reported here. Results suggest that the efficacy of Geocoris as a biocontrol agent changes throughout the season, and may be influenced by their natural enemies.

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