Predatory Performance of Microvelia douglasi Scott (Hemiptera: Veliidae) with Reference to Diel Periodicity

Abstract

The present work centers on the predatory performance of Microvelia douglasi adults with reference to diel periodicity. This experiment attempts to determine on whether the foraging efficiency was more at diurnal or nocturnal period, and was there an endogenous rhythm available within them to activate foraging response. The study was conducted in the laboratory for 24 hr with an interval of every three hr. The experiment was divided into Phase I (LD 12:12) and Phase II (DL 12:12). The predatory efficiency of M. douglasi adults was investigated on the first and second instars of Anopheles stephensi at prey densities of 25 and 50, and the experiment was conducted separately for male, female, and for both male and female, in 500 mℓ and 1000 mℓ containers. The bugs showed predatory activity both in diurnal and nocturnal periods. In LD cycle, maximum predatory activity was at 15:00 hr by the female bugs, and a total of 350.0 An. stephensi larvae were predated with 144.6 and 205.4 prey predated at 25 and 50 prey density, respectively. The male bugs predated 110.4 prey, and their response was less than that of females, which showed the highest rate of predation as they predated 129.4 prey. The prey predated when both male and female were put together was 110.2. In DL cycle, maximum predatory activity occurred at 24:00 hr again by the female bugs, and a maximum of 327.8 larval instars were predated with 153.4 and 174.4 prey predated at 25 and 50 prey density, respectively. Female bugs predated (121.2) more prey than male (99.4). However, the prey predated when both male and female were put together was 107.2, which was higher than prey predated by male. In LD cycle, the bugs predated more first instar (186.0) than the second instar (164.0), and in DL cycle, there was not much difference as 163.2 and 164.6 first and second instar, respectively were predated. Overall, the bugs showed more predatory activity during light than in dark, though natural light was changed to dark and dark to light. Predator’s sex, prey size, and different photoperiods testified the predatory performance of M. douglasi, and it was noted that the cumulative interactions of these three parameters were significant. The photoperiods were highly significant. Relatively high statistical significance was also derived in the interaction between the prey size and photoperiod. There was no statistical significance between predator’s sex and prey size and predators’ sex and photoperiod, and when all three parameters interacted, very less significance occurred.