Changing Patterns of Prey Consumption in the Predatory Larvae of Toxorhynchites Brevipalpis (Diptera: Culicidae)1

Abstract

Fourth-instar Toxorhynchites brevipalpis larvae change their predatory behavior as their development proceeds from molting to pupation. The predatory larvae start feeding about 2 h after molting to 4th instars. Generally 2 kinds of larvae were observed in this study: (1) larvae that consume high numbers (25 or more) of prey larvae during the first 24 h of their 4th larval instar, and (2) larvae that consume few (10 or less) prey larvae during the first 24 h. The former reach peak prey consumption within 3 days and the duration of their 4th larval stadium is 8 to 10 days. The latter increase their prey consumption progressively from the 1st to the 7th day, when they reach their peak daily consumption. After the 7th day prey consumption decreases as the larvae approach pupation, and about 20 h before pupation larvae stop eating. The curve for prey consumption of the 1st type of larvae is skewed to the right, while the curve for prey consumption of the 2nd type approximates normal distribution. It is suggested that this might be a case of behavioral polymorphism, which may control population density of the predator as seasonal population density of prey increases or decreases.