Within-plant distribution of thrips and their predators: Effects of cotton variety and developmental stage

Plant characteristics often influence the distribution of herbivores and natural enemies. In turn, the degree of their spatial association is likely to influence the ability of natural enemies to control pests. Also, an understanding of pest distribution patterns is important for the development of reliable and cost-effective sampling protocols. In this study, we assessed the effect of cotton variety and developmental stage on the within-plant distribution and degree of spatial overlap between populations of two thrips species and their predators. In the two studied varieties, cv. Pima and Acala, almost all Thrips tabaci Lindeman inhabited the leaves, while Frankliniella occidentals (Pergande) colonized only the flowers. With respect to the predators, most Chrysoperla carnea (Stephens) were found on the leaves of both varieties, whereas predatory Orius spp. colonized mainly the flowering structures on Pima plants but the leaves on Acala. This variability in prey and predator distribution resulted in a significant and positive correlation between thrips and predator populations on Pima but not on Acala plants. The results also suggest that, overall thrips are most likely to be preyed upon on squares and to be relatively safe in flowers. An intermediate but relatively high risk of predation apparently occurs on the leaves. The significance of these within-plant distribution patterns for the monitoring of thrips populations is discussed.