A move towards maximizing natural biological control of pink bollworm, Pectinophora gossypiella (saunders) (lepidoptera: gelechiidae) in Sindh, Pakistan

Abstract

Continuous reduction in cotton production is seen in Pakistan due to arthropod infestations, especially pink bollworm, Pectinophora gossypiella (Saunders), that has become a major pest in recent years, is next to impossible to be controlled by insecticides. Consecutive use of insecticides in crop has weakened the natural biological control of pink bollworm (PBW), impacting crop yield. Parasitoids and predators are regarded most eminent biological control agents of PBW worldwide. Rich natural enemies complex comprising 28 parasitoids species and 23 of predators has been reported associated with PBW in Pakistan. A wealth of knowledge is available on indoor parasitoids rearing and manual release in fields, but little is known on mass multiplication of parasitoids in field conditions and their natural dispersion. The role of innovation of establishing outdoor facility to say natural enemies’ field reservoir (NEFR), was tested for mass production of parasitoids and their dispersion naturally, to maximize natural biological control of PBW in District Sanghar. Twelve NEFR sheds/shelters, open from all sides, were built at variable distances of 5-10 km from one another to cover 2400 acres of cotton crop. At shelters PBW infested flowers and bolls were kept for 15-20 days in zincoid trays and transparent plastic jars, covered with net of adequate hole size that allowed easy escape of parasitoids and held back the PBW moths. To start with, observations were made in March-June 2021 to confirm presence/absence of PBW parasitoids in flowers and bolls, whereas from July onwards, not only activities were confined to mass production of parasitoids but also determined parasitism rate in PBW for indirect estimates of parasitoids dispersing in the environment. Large collection of PBW larvae (about 12 million) was also made in November and December from ginning mills refuse (cotton seeds and fibers), and kept in trays at 12 NEFR shelters. Most of parasitoids recorded were solitary but some of them were gregarious, such as Bracon gelechiae. Variable parasitism rates were observed in PBW larvae and pupae collected from different sources being highest (43%) in rosette blooms followed by cotton bolls (31%) and ginning wastes (23%). Out of 7.8 million larvae and pupae collected in July- November from green and harvested crop wastes, were obtained 2.1 million parasitoids. More advantage of NEFR was of eradication of 5.7 million PBW moths (males and females) from cotton environment. Thus, besides conservation of parasitoids, millions of PBW adults were destroyed that probably was not possible with pesticides sprays in the field. Observations on slow emergence of pest and parasitoids from mills refuse continued through February 2022. These findings are food for thought to move forward for promotion of NEFR like resource conserving technologies for sustainable management of insect pests.