RESOURCE CONCENTRATION HYPOTHESIS - EFFECT OF HOST-PLANT PATCH SIZE ON DENSITY OF HERBIVOROUS INSECTS

The resource concentration hypothesis (Root 1973) predicts that specia list herbivorous insects should be more abundant in large patches of h ost plants, because the insects are more likely to find and stay longe r in those patches. Between August 1989 and January 1990 we experiment ally tested Root's hypothesis by analyzing the numerical response of f our species of herbivorous insects associated with patches of 4, 16, 6 4 and 225 cabbage plants, Brassica oleracea var. capitata. In addition , we studied the colonization of patches by adults of Plutella xyloste lla (L.) (Lepidoptera: Plutellidae), and the migration of their larvae in patches of different sizes. No herbivorous insect densities differ ed significantly with patch size. Adults of P. xylostella colonized al l kind of patches equally. Larvae did not migrate between patches, and their disappearance rate did not differ between patches. The resource concentration hypothesis is organism-dependent, being a function of t he adult and juvenile herbivore dispersal behavior in relation to the spatial scale of patchiness.