Nutritional efficiency of the potential biocontrol agent Galerucella placida Baly on different species of polygonaceae weeds

Polygonum generally known as Knotweed is a large genus consisting of weedy plants. Many species of polygonaceae family are the weeds especially in the irrigated rice cultivation and tea estates of North East India. As there is expected level of potentially hazardous to environment due to the chemical control measures for this weed which is also a costliest one and requires long term application with the cost of detrimental effects on non target wetland plants. Biological control offers the most logical approach for controlling the weed in the most effective and least environmentally damaging way. Chrysomelidae leave beetle Galerucella placida Baly is the insect feeds on aquatic weeds of polygonaceae which can be utilized for the biological control programme. In order to find the efficiency of Galerucella placida on different species of Polygonaceae weeds, different nutritional indices such as approximate digestibility (AD), relative consumption rate (RCR), relative growth rate (RGR) and efficiency of conversion of digested food (ECD) are tested under the laboratory condition. The relative growth rate (RGR) and the relative consumption rate (RCR) of G. placida was highest on P. hydropiper (Linn.) Spach as (0.10 mg/day/mg) and (2.04 mg/day/mg) respectively which was found to be lowest on P. perfoliatum Linn. (0.07 mg/day/mg) and P. perfoliatum Linn. (0.07 mg/day/mg) respectively. The highest value of approximate digestibility (AD) was recorded in case of P. densiflorum Blume (97.89%) followed by P. minus Huds. (96.73%). Efficiency of conversion of digested food (ECD) was highest in case of P. perfoliatum Linn. (8.92%) followed by P. minus Huds. (6.17%) and lowest on P. hydropiper (Linn.) Spach (4.22%). Similarly larvae fed on P. perfoliatum Linn. (8.19%) had the highest value of efficiency of conversion of ingested food (ECI) and the lowest on values of ECI were in the larvae reared on P. hydropiper (Linn.) Spach (4.01%).