Natural Field Parasitization of Groundnut Leaf Miner, Aproaerema modicella (Deventer) and Influence by Weather Parameters in Rainfed Groundnut Ecosystem

Background: Groundnut (Arachis hypogea L.) is one of the most important oilseed crops in India, playing a crucial role in the country’s economy. This crop is vulnerable to various insect pests starting from vegetative to maturity phase, of which, the leaf miner Aproaerema modicella (Deventer) (Lepidoptera: Gelechiidae) cause substantial yield loss especially in rainfed groundnut cultivation. Most of the farmers were reluctant to adopt integrated management strategies and prefer to take up only chemical pesticides. Biological control is one of the effective management options since the groundnut ecosystem harbours several biological agents. Natural biocontrol agents including hymenopteran parasitoids like Bracon gelechiae, Goniozus sp., Apanteles sp., Stenomesius japonicus etc. plays a vital role in managing the pest under irrigated ecosystem. Only limited studies were available on the effectiveness of these natural bio-control agents in rainfed ecosystem and hence, present study was focused on the natural parasitization of A. modicella in rainfed groundnut ecosystem. Methods: The field survey was conducted during Summer and Kharif, 2023 in Nambiyur block, Erode District, Tamil Nadu, India to record the natural parasitization percentage on 10 randomly selected plants at weekly interval. The parasitized larva and pupa of A. modicella were collected and reared under laboratory conditions to record the emergence of parasitoids The natural parasitization was correlated with the weather parameters prevailed during the cropping season. Result: Bracon sp. has been identified as the major natural enemy of A. modicella under rainfed ecosystem. During Summer 2023, minimum parasitization level of 8.0 per cent was observed in the 12th Standard Mean Week (SMW) i.e., second fortnight of March. Subsequently, the parasitization levels were increased during Kharif, 2023 with the moderate (18.00%) during 23rd to 30th SMW i.e., June-July and peaked (26.00 %) during 31st to 33rd SMW i.e., July-August months. The correlation analysis results revealed that the maximum temperature (0.768), minimum temperature (0.533), rainfall (0.015) and Sunshine hours (0.483) were positively correlated and Relative humidity (-0.146) was negatively correlated with the per cent parasitization.