The status of resistance to phosphine in common bruchid species infesting edible stored pulses in India

Abstract

Bruchids or pulses beetles or bean weevils (Coleoptera: Chrysomelidae: Bruchinae) are serious pests of stored pulses, and the only curative chemical option approved for use in India is fumigation with phosphine. Relative phosphine resistance was ascertained in 79 bruchid populations from 74 diverse locations of India, in comparison to their susceptible laboratory conspecifics. The populations' response to phosphine was varied vis-à-vis species, locations, and storage conditions. Overall, the populations recorded the relative resistance ratio of 1.1–4.5 folds over their susceptible laboratory conspecifics, however the LC99 values indicated populations are still susceptible to recommended phosphine dosage by Central Insecticide Board and Registration Committee. The relative resistance levels in decreasing order for species was Callosobruchus maculatus > C. analis > C. chinensis. The populations from small-scale storage conditions exhibited relatively lower level of resistance than those from large-scale storage conditions. The relative resistance was varied between populations representing different states and regions of India. The populations from places where pulses are grown, stored and protected with phosphine on a large-scale and regular basis showed higher relative resistance. When compared to species infesting stored cereals, the relative resistance levels recorded in bruchid populations was rather low; however, the observed levels warn of further escalation to an alarming level in the events of inappropriate and indiscriminate phosphine usage. Consequently, the Indian pulses storages fully reliant on this fumigant may face a significant bruchid threat in the near future. Therefore, the current study provides a valuable source of information on phosphine resistance status in bruchids infesting edible stored pulses across India.