Performance and field efficacy of indigenous egg parasitoid Trichogrammatoidea bactrae (Hymenoptera: Trichogrammatidae) against the cotton pink bollworm Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) in transgenic Bt cotton

Abstract

The pink bollworm (PBW) Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) has emerged as a major pest of transgenic Bt cotton in India. The recent outbreak of PBW caused serious damage, and the existing management strategies become inefficient to reduce the pest incidence and crop yield losses. The development of environment-friendly and sustainable management strategies against PBW is urgently needed. Thus, laboratory tests were performed to evaluate 16 indigenous trichogrammatid species/strains to manage the PBW in transgenic Bt cotton. We compared the parasitism of trichogrammatid species/strains on PBW eggs and found that Trichogrammatoidea nr. robusta (79.6%), Trichogrammatoidea bactrae Nagaraja (76.4%) and Trichogramma chilonis Ishii (73.8%) parasitized a greater percentage of PBW eggs under laboratory conditions. Furthermore, the parasitism of Tr. nr. robusta, Tr. bactrae and T. chilonis were tested in cages. Results of cage study showed that Tr. bactrae parasitized at a higher rate the PBW eggs (73.2%) followed by T. chilonis (60.5%) and Tr. nr. robusta (48.6%). Subsequently, the effectiveness of Tr. bactrae was assessed for consecutive three years (2017–2020) in transgenic Bt cotton fields. We found that the 12 sequential releases of Tr. bactrae from the flowering stage onwards showed a significant reduction in the PBW incidence. Field released with Tr. bactrae or treated with insecticides reduced the number of larvae boll−1 by 1.5 and 3, respectively, the percentage of rosette flower by 1.7 and 2.7, respectively, and the percentage of locule damage by 2 and 2.5, respectively, compared to untreated control field. A higher yield of seed cotton was obtained both in Tr. bactrae released field (27.73 q h−1) and insecticide treated cotton field (31.68 q h−1) as compared to untreated control field. Our results showed that Tr. bactrae is a potential biocontrol agent of PBW. This could be used in biological control programme and may be incorporated in integrated pest management (IPM) programme against PBW in transgenic Bt cotton.