Do pigeon pea refuges in Bt cotton pull their weight as "genetic diluters" to counter Bt resistance in Helicoverpa moths?

Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) are destructive pests that could develop resistance to Bt-cotton (Gossypium hirsutum L.). In Australia resistance is countered within a season by diluting resistance genes with susceptible genes (“Genetic Dilution”); or limiting the gene flow of resistance genes between seasons (“Season Quarantining”). Planting non-Bt host plants (“refuges”) like pigeon pea (Cajanus cajan (L.)) to produce sufficient susceptible genes to dilute resistance genes from Bt-cotton, is part of the Genetic Dilution strategy. The current resistance management plan for Bt-cotton mandates that pigeon pea refuges are half the size of non-Bt-cotton refuges because pigeon pea can produce twice as many moths as cotton. We tested this assumption on commercial farms using eggs and pupae of both Helicoverpa species as measures of attractiveness and productivity respectively. We found that pigeon pea attractiveness and productivity is inconsistent across the season and that, compared to cotton, higher egg densities in pigeon pea were concentrated at the end of the season. We discuss the implications of these data in terms of the pros and cons of following the Genetic Dilution strategy and maintaining pigeon pea refuges for as long as possible, versus destroying pigeon pea refuges at the end of the season as part of a Season Quarantining strategy.