PREY SHIFT AND PREDATORY PERFORMANCE IN DIPLONYCHUS RUSTICUS (FABRICIUS, 1871) AGAINST TWO DIFFERENT PREYS

In food web of fresh water communities the aquatic and semiaquatic bugs plays a vital role in effectively controlling the larval forms of certain disease spreading insect vectors by feeding them voraciously. Since Diplonychus rusticus is polyphagous and carnivorous predator, the present study was undertaken to observe the effect of prey shift and experience on predation in Diplonychus rusticus exposing them to Culex and Chironomous larvae for 10 day duration alternatively. Adult male water bugs, prestarved for 10 days, were exposed to individual prey item at prey density of 200 for one day in a container filled with 1 litre of dechlorinated tap water and the number of prey killed was recorded after 1 hour and 24 hours. This experiment was carried out for 10 days. The prey shift mechanism was assessed by following the same procedure, exposing the adult male bugs to Chironomous larvae from the 11th day after feeding them with Culex larvae for 10 days. The number of prey killed by the predator after 1 hour and 24 hours were counted and recorded. Ten trials were carried out to draw the mean and standard deviation for both the prey items. The number of Culex larvae killed by the predator was initially high and on the 10th day it declined in 24 hours. The predatory performance was initially declined on 11th day and gradually increased on 20th day when subjected to Chironomous larvae in 24 hours. Statistical analysis was determined using Roger’s equation (1972) of under non-linear square technique. As far as the prey preference is concerned, the result reveals that Diplonychus rusticus preferred Culex larvae than that of Chironomous larvae for 10 day duration. Key words: Prey shift, Belostomatid bug, Culex larvae, Chironomous larvae, Diplonychus rusticus.