Thursday, August 6, 2009

PS 63-43: Does controlling beet leafhopper impact the endangered blunt-nosed leopard lizard (Gambelia sila)

Richard A. Redak, Kathleen A. Campbell, and Thomas R. Prentice. University of California

Background/Question/Methods
Beet curly top virus is a debilitating plant pathogen to several important agricultural crops of California and is transmitted by the sugar beet leafhopper, Circulifer tenellus (Baker) (Homoptera: Cicadellidae). Crop damage by this insect-virus association is controlled by (1) cultural practices that seek to remove host plants of the insect vector, (2) the use of pathogen resistant plants, and (3) direct management and control of the insect vector. Direct management and control of this insect typically involves treating non-agricultural habitats into which the insect migrates during late fall and winter. Treatment of these areas is performed through the aerial application of malathion. Concerns involving the treatment of non-agricultural areas for sugar beet leafhopper control have emerged due to potential effects of insecticide treatments on the food resource base (predominantly arthropods) of the endangered blunt-nosed leopard lizard, Gambelia silus. The impacts of malathion treatments upon arthropod communities within G. silus habitat or upon the food resource base of G. silus are unknown, and their determination is the objective of this study. Over a three-year period, we estimated arthropod species richness and abundance in malathion-treated and untreated plots.  Richness and abundance were estimated from insects collected from pitfall and malaise traps. Comparisons of arthropod biodiversity estimates were made between treatments using repeated measures ANOVA and rarefaction analysis.
Results/Conclusions

Our results indicate that the overall impact of malathion treatments on arthropod abundance was minimal. Variation in abundance due to annual, seasonal, and spatialfactors was far greater than any variation due to insecticidal treatment.  Although there were seasonal and annual changes in arthropod community structure and speciesrichness between and within years, this impact was not consistent across all years of the study. For ground dwelling arthropods, a significant negative impact on community structure and species richness with treatment was only evident in the terminal year of the study. For flying insects, treatments negatively impacted community structure with a reduction in species richness in two out of the three years examined.  As the blunt-nosed leopard lizard is an opportunistic and generalist predator, we believe our data demonstrate that minimal impact on the food resource base of blunt-nosed leopard lizard will occur with these type of treatments. Although there may be significant changes in species richness and community structure with treatment, there is little impact on overall abundance of potential “food” (=abundance) for the lizard.


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