Abstract:
Xenylla welchi was used to evaluate toxicity of two herbicide formulations, pretilachlor (50 EC) and pendimethalin (30 EC) under laboratory conditions. Twenty four hours LC50 value of pretilachlor and pendimethalin formulations on Xenylla welchi were 72.7 and 190.0 g a.i/ ha respectively which were less than their corresponding recommended agricultural doses. Again pretilachlor attained fastest LT50 (110 min) followed by pendimethalin (140 min). Significant reductions in hatching success were noted with the application of both the herbicide formulations at all doses excepting 1/8 and 1 /10th of LC50 (9.1, 7.3 and 23.8, 19.0 g a.i/ha for pretilachlor and pendimethalin, respectively). Hatching success of the test specimens recorded 44.1 and 63.3% reduction from control for the highest applied dose ( of LC50) of pretilachlor and pendimethalin, respectively. Juveniles of Xenylla welchi exposed to 1 /6, 1 /8 and 1 /10th LC50 for pretilachlor (12.1, 9.1, 7.3 g a.i/ha) and 1 /8 and 1 /10th LC50 for pendimethalin (23.8, 19.0 g ai/ha) survived and exhibited increased moulting frequency (7 moultings in 28 days in both the herbicide treatments) in comparison to control (8 moulting in 42 days). Test specimens required 26.0 ± 1.2 and 28.1 ± 2.1 days to attain sexual maturity exposed
to pretilachlor and pendamethalin respectively which was significantly less than control (42 ± 2.6 days). Several works have been done to find out the impact of herbicides that are frequently used in agro-farming on non target soil organisms like collembolans. However, little data is available for the tropical conditions. Notable contributions among them are by Bhattacharya and Joy (1980a, b), Joy and Bhattacharya (1981), Mitra et al. (1983), Bandyopadhya (1995), Park and Lees (2005), Amorim et al. (2005), Frampton et al. (2006) and Lins et al. (2007). There are evidences that collembolans are more susceptible to pesticides than other soil arthropods. In the present study, the effects of two selected herbicide formulations were evaluated on Xenylla welchi (Collembola—Hexapoda) under laboratory conditions. Herbicide formulations tested were pretilachlor and pendimethalin which were easily available in local markets and commonly used by farmers. Main purpose of the present study was to evaluate the comparative toxicity of the two herbicide formulations on Xenylla welchi and their potential to damage soil ecosystem.
