Toxicity and sub-lethal effects of temephos, lambda-cyhalothrin and cypermethrin on predatory insect Diplonychus rusticus Fabricius (Hemiptera: Belostomatidae)
2021
Reegan, Appadurai Daniel | Bentrock, Bosvin Ben | Asharaja, Antony Cruz | Tennyson, Samuel | Raveen, Rajasingh
Diplonychus rusticus (Heteroptera: Belostomatidae) is relatively a bigger sized tropical water insect serves as a main predator of mosquito larvae. In the present study, toxicity and effects of three different insecticides viz., temephos, lambda-cyhalothrin and cypermethrin was evaluated on D. rusticus. The results showed that the cypermethrin exhibited highest toxicity with lowest LC₅₀ and LC₉₀ values of 0.02 and 0.12 ppm on D. rusticus. Observations showed that the functional response greatly varied with all the three insecticides. The mean number of preys consumed at the density of 64 larvae was significantly different among the treatments. The mean longest handling time of 4.18 ± 0.34 and the mean lowest attack rate of 0.015 ± 0.008 were observed in lambda-cyhalothrin and cypermethrin treatments, respectively. The adult longevity of D. rusticus was found to be very less (42.33 ± 1.52 days) in cypermethrin treatments, whereas it was 113 ± 1.73 days and 120 ± 2.64 days in lambda-cyhalothrin and temephos insecticides, respectively at 0.01 concentration. The coupling behavior of the insect was noted to occur very rarely in all the three insecticide treatments. The total number of eggs layed was 16 eggs and 26 eggs in lambda-cyhalothrin and temephos treatments at 0.01 concentration, respectively. Furthermore, it was noted that there are no eggs were hatched (0%) from these egg clusters. These results indicate that the tested insecticides exhibited sub-lethal effects on the predatory insect D. rusticus.
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