Effect of herbicides on digestive enzyme activity of epigeic indigenous earthworm perionyx excavatus (oligochaeta)

Different levels of two herbicides Pendimethalin and Pretilachlor based on their recommended agricultural doses (RAD) were administered into the testboxes with a micropipette (Lofs-Holmin, 1983) with five numbers age synchronized specimens of Perionyx excavatus in each box. The 96 hrs acute toxicity tests showed that Pendimethalin with an LC50 value of 0.022mg/kg soil was more toxic than Pretilachlor, LC50 value 0.094 mg/kg soil. Open choice experiment was done on indigenous epigeic earthworm Perionyx excavatus with Anacardium occidentale (cashew), Mangifera indica (mango), Shorea robusta (shal), Acacia auriculiformis (Acacia) and Eucalyptus citridora (Eucalyptus), leaves to determine their food preference. In the feeding preference experiment the earthworms showed maximum preference for Anacardium occidentale (cashew) leaves. The activity of the digestive enzyme α-amylase was determined under laboratory conditions in natural garden soil by exposing the earthworms to sub-lethal doses of the two herbicides i.e., 25% and 50% of LC50 value, determined earlier. The activity of the enzyme, in Pendimethalin, grew significantly higher than the control value on the 15th day of the experiment In case on the 30th day of the experiment, the enzyme activity is decreased in both the sub-lethal doses i.e. 25% of LC50 and 50% of LC50 which are significantly lower than the control value. Pendimethalin was found more toxic than Pretilachlor but was less harmful to chronic exposure to the earthworms.