Effect of food on immature development, consumption rate, and relative growth rate of Toxorhynchites splendens ( Diptera: Culicidae ), a predator of container breeding mosquitoes

Food utilization by the larvae of Toxorhynchites splendens (Wiedemann) was studied in the laboratory by offering larvae of Aedes aegypti Linnaeus, Anopheles stephensi (Liston), and Culex quinquefasciatus (Say). Quantitative analyses of data indicated that immature development was significantly faster with increase in food availability. The regression analysis showed that the degrees of the relationship between immature duration (Id) and food availability were higher when offered early instars of prey (first and second instars) than late instars. Consumption rate (Cr) of the predator increased with increase in food availability and this relationship was highly significant when larvae of An. stephensi were offered as food. Consumption rate to food level decreased with increase in the age class of the prey. There was a significant negative correlation between Id and Cr. This aspect helps to increase population turnover of T. splendens in a shorter period when the prey is abundant. Conversely, the predator compensated the loss in daily food intake at low food level by extending Id thereby attains the minimum threshold pupal weight for adult emergence. There was an increase in the relative growth rate (RGR) of the predator when An. stephensi was offered as prey and this was related to the high protein content of the prey per body weight. There was a positive correlation between Cr and RGR. This adaptive life characteristic strategy of this predator is useful for mass-rearing for large scale field release programmes in the control of container breeding mosquitoes is discussed.

Estimation of predation by the larvae of Toxorhynchites splendens on the aquatic stages of Aedes aegypti.

Predation by instars of Toxorhynchites splendens on aquatic stages of Aedes aegypti was studied by estimating functional response parameters such as attack rate (a') and handling time (Th) in the laboratory. The predator displayed typical type-II functional response, similar to that of most insect predators when presented with increasing densities of any given size class of prey. Second instar predator attacked prey significantly at higher rate than the other instars. Small prey were attacked at higher rate than the predation on larger prey. Except second instar predator, other instars showed significant reduction in a' with increase in Th. Foraging surface area did not influence the predation rate. Predation was high at high water temperature and this was more prominent in the second instar predator. However, prey handling time was independent of the water temperature. Modeling of the predation of mixed age populations of prey and the predator through this short-term functional response experiment is discussed.