Biological traits associated with Cry1Ac resistance in <em>Helicoverpa</em> <em>armigera</em> (Lepidoptera: Noctuidae)

Abstract

The cotton bollworm, <em>Helicoverpa armigera</em> (Hübner) is an important cotton pest worldwide, and it causes losses up to 30% of the total cotton production in India. Though the insecticidal crystal (Cry) proteins produced by <em>Bacillus thuringiensis</em> (Bt) have been effective against lepidopteran pests, evolution of resistance has become an issue of concern. Study of fitness costs associated with resistance to <em>Bt</em> Cry toxins gives an insight to resistance evolution and helps in effective resistance management. Here, we studied a number of biological traits of resistant and susceptible population of <em>Helicoverpa armigera</em> on Cry toxin treated and untreated diet to understand the association between Cry1Ac resistant and biological traits. Isofemale lines were obtained by single pairing of field collected <em>H. armigera</em> population. The F₂ of the isofemale line were assayed at concentration of 1 and 10 µg of Cry1Ac/g of diet. The line which showed highest survival percentage was the resistant line DNDT-R and the line which showed the lowest survival percentage was the susceptible line M4-S. Biological traits were studied by conducting crosses and backcrosses of the resistant and susceptible line. The F₁ progeny and resistant parent showed significantly better performance than the susceptible parent in various biological parameters. The per cent pupation and adult emergence were higher in F₁ and F₂ generations than the susceptible parent and also between resistant and F₁ on both treated and untreated diet. This finding is important to know the fitness cost expressed by resistant population over susceptible population so as to delay resistance development.