Document: PAT-3-61-3

The impact of spiders and carabid beetles on the abundance of insect pests and potato yield.

VICHITBANDHA, P.* ^1,2 and D.H.WISE ¹

University of Kentucky, Lexington, KY 40546, USA ¹
Kasetsart University, Kamphaeng-Saen, Nakorn Pathom, Thailand ²

Abstract:
The extent to which spiders and carabid beetles limit populations of insect pests and enhance potato yield was determined in two different field experiments conducted in consecutive years. The experiments employed a combination of mulching, fencing, hand-removal, and live pitfall trapping (3 replicates / treatment) to alter densities of indigenous spiders and carabid beetles that immigrate into gardens from surrounding habitats. In Year 1, Kennebac and Red Pontiac potatoes were planted with cucumbers and eggplant in 105-m² plots. In Year 2, a monoculture of Kennebac potatoes was planted in 64-m² gardens. In Year 1, densities of Colorado potato beetles (CPB) were 3x higher (p = 0.065) and yield of Kennebac potatoes was 35% lower (p = 0.082) in fenced, predator-reduction plots compared to open controls. These marginally significant effects disappeared in Year 2, when densities of CPB and potato yield were similar in fenced removal, fenced control and open control plots (p's > 0.50). At least two factors likely contributed to the absence of control of CPB in Year 2: (1) predation by spiders and carabids also affected densities of several other predators of insect pests: predaceous damsel bugs, big-eyed bugs and lacewings; and (2) CPB densities in open control gardens were >10x higher in Year 2 than the preceding year. Future studies are needed to quantify the indirect effects of spiders and carabids on other natural enemies, and to determine threshold densities of CPB below which spiders and carabids can limit densities of this major pest of potatoes.

Keywords: Araneae, Carabidae, Colorado Potato Beetle, Field Experiment, Potato

This abstract is being presented at: 4:00 PM in session:
Oral Session #31: Agroecology.