Acute Toxicity of Botanical Pesticides, Neem Oil (<i>Azadirachta indica</i>) and <i>Polygonum hydropiper</i> Leaf Extracts in Fingerlings of <i>Catla catla</i> (ham.)

Abstract

Use of botanical pesticides is considered a safe and environment friendly method for controlling rice insect pests in lowland. To explore the possibility of using neem oil (Azadirachta indica) and the leaf extract of Polygonum hydropiper (a lowland weed) as botanical pesticides against rice insect pest in lowland rice-fish ecosystem, acute toxicity experiments were conducted in control condition using fingerlings of Catla catla (4.4±0.4 g, 7.3±0.6 cm) as the test fish. The botanicals were applied as emulsion by adding ‘labolene’ (a liquid detergent) as the emulsifier to neem oil and grinded leaf of P. hydropiper. The immediate knockdown effect in terms of fish mortality was recorded in both the botanicals within first 24 hours of application. No fish mortality was observed after 24 hours indicating faster biodegradation of these toxicants. The 24 h LC50 were found to be 36.6 l/l for neem oil and 4.6 mg/l for leaf of P. hydropiper. These concentrations are much higher than the recommended dose applied against insect pest in rice crop. The study indicates that these two botanicals can be used in rice-fish ecosystem at their recommended dose level for control of rice insect pest without any fish mortality.