Monitoring insecticide resistance in Bemisia tabaci mitotypes in the South Punjab region of Pakistan

Whitefly (Bemisia tabaci Gennadius) (Hemiptera: Aleyrodidae) is a serious pest of several summer crops in hot and dry climates with diverse cryptic species complex worldwide. Cotton is one of the favorite hosts of B. tabaci, where it feeds and spread different plant viruses. The major clade of B. tabaci; Asia-II is predominant in the cotton zone of Punjab-Pakistan. The control of B. tabaci in cotton ecosystem mostly depends upon the sprays of synthetic insecticides in Pakistan. Monitoring of insecticidal resistance is an essential tool in effective management of B. tabaci. Different cotton field strains were collected from the four major cotton growing districts of South Punjab to assess their genetic mitotype and resistance levels compared with the laboratory susceptible population against most commonly used insecticides during 2020 and 2021. Leaf-dip bioassays were performed on 2nd instar nymphal (N2) stage; while adult bioassays were conducted on field collected populations. Genetic analysis of mtCOI revealed that all the populations were belonged to Asia II-1 clade. A mixture of three haplotypes of Asia II-I including haplotypes-2, haplotype-3 and haplotype-4 was identified from Jampur and Bahawalpur samples. However, haplotype-4 and haplotype-3 were identified from Multan population while Vehari samples comprised of haplotype-4 and haplotype-2. Buprofezin (RR ranged 25.75-36.71), pyriproxyfen (RR ranged 7.98-12.78) and diafenthiuron (RR ranged 20.59-28.12) were least efficient products in adult bioassays and had moderate to low level of resistance. However, spirotetramat and flonicamid both were relatively effective against adults with low to very low resistance during both the years. Pyriproxyfen demonstrated least efficacy for reducing adult emergence followed by flonicamid and buprofezin with moderate to very low resistance ratio respectively. In contrast spirotetramat (RR ranged 2.20-4.01), was highly effective against nymphs followed by diafenthiuron (RR ranged 4.63-7.68), having very low resistance ratio. However an upward trend of resistance development was observed against all the five tested insecticides during both the monitoring years. It can be concluded that, in the aftermath of the emergence of resistance to old conventional insecticides, various chemistries with unique modes of action having no, very low, or low levels of resistance can be substituted in rotation.