Natural parasitism by trichogrammatids (Hymenoptera: Trichogrammatidae) on lepidopteran eggs under diverse cropping system

Abstract

The present study was conducted to collect and identify the species of trichogrammatids from eggs of lepidopteran pests infesting the diverse cropping systems in the country. A total of 28 plant species were inspected for the collection of lepidopteran eggs either through collection of insect eggs or by placing sentinel egg cards. The species such as Trichogramma chilonis Ishii, T. achaeae Nagaraja and Nagarkatti, T. danausicida Nagaraja, Trichogrammatoidea bactrae Nagaraja and Tr. armigera Manjunath were recorded naturally occurring with 12 species of lepidopteran insect pests. In nature, the parasitism rate varied from 5.35 to 82.25% by the associated trichogrammatids. A total of 596 sentinel trap cards were placed in the agricultural, vegetables, fruits crops, and grasses on the bunds of fields to trap the egg parasitoids present in the different habitat. Through sentinel cards, three species, viz., T. chilonis, T. achaeae and Tr. bactrae were found inhabit the vegetables and ornamental crops. The percentage of adult emergence from the sentinel trap cards ranged from 70.59 to 100.0%. Natural parasitism of Tr. bactrae recorded for the first time on the eggs of Lampides boeticus L. infesting wild species of Crotalaria. In addition, the natural parasitism of Tr. armigera and Tr. bactrae on the eggs of L. boeticus laid on either cultivated or wild relatives of Crotalaria in undisturbed habitat had higher natural parasitism due to their bright yellow flower attracts parasitoids to parasitize the eggs and conserve these egg parasitoids. Recently, natural parasitism of Trichogramma sp. was recorded on invasive fall armyworm, Spodoptera frugiperda (J.E. Smith) infesting maize in Karnataka. Based on the present work, there could be choice of selecting right species which occur naturally on individual crops.