EFFECTIVENESS OF LARVAL DEFENSES AGAINST SPIDER PREDATION IN CRANBERRY ECOSYSTEMS

Two laboratory experiments, a choice test and observations of individu al spider-larva interactions, were conducted to determine how the morp hological or behavioral defenses, or both, of larvae may affect spider predation success for 2 genera of spiders [Pardosa (Lycosidae), and H abronattus (Salticidae)] commonly found in Massachusetts cranberry, Va ccinium macrocarpon Aiton, ecosystems. Four species of pest larvae wit h different potential de fenses were offered as prey: a spanworm, Emat urga amitaria Guenee (Lepicloptera: Geometridae); a sawfly, Pristophor a idiota Norton (Hymenoptera: Tenthridinae); gypsy moth, Lymantria dis par L. (Lepidoptera: Lymantriidae); and a fruitworm, Sparganothis sulf ureana Clemens (Lepidoptera: Tortricidae). In the choice tests, E. ami taria larvae were killed significantly more often than either P. idiot a or S. sulfureana larvae. No L. dispar larvae were killed in either e xperiment, and observations suggested that the long setae of the L. di spar larvae provided defense against spider attack. Observations revea led that behavioral and morphological crypsis was a more effective def ense than thrashing and regurgitating when E. amitaria larvae were enc ountered by either genera of spider and also suggested the presence of a chemical defense(s) in P. idiota larvae. Construction of a retreat in cranberry foliage and wriggling movements by S. sulfureana larvae w ere highly effective in deterring salticid predation. We conclude that the defensive mechanisms possessed by these larvae may effectively in fluence prey selection and significantly limit predation by spiders in the cranberry agroecosystem.