Abstract:It is a key step for cotton bollworm (CBW) management to determine the ratio of moths of cotton bollworm originating from C3 and C4 host plants for the overwintering generation and their contribution to the next spring first generation in North China. In this study, the development times of larva from the female moths captured in wheat field in 2007 were observed systematically. Moreover, δ13C values in the wings of each female moth were tested with GC-MS apparatus to determine larval host plant type. Results showed that 53.1% of moths trapped during spring emergence (the overwintering generation CBW) came from larva grown in late autumn C3 host plants (cotton), 46.9% came from larva grown in late autumn C4 host plants (corn). 57.9% of eggs laid by the overwintering generation moths were determined as progeny of C3 phenotype via stable isotope examination on the wings of moth, individually. Significantly higher hatching rate were observed in the eggs laid by the moths from larva grown in C3 host plants than C4 host plants. Furthermore, about 63.7% first instar larva on spring wheat was determined as progeny of C3 phenotype moths. Moreover, about 47.9% larva at the third instar, 45.5% fourth instar larva, 46.9% fifth instar larva, 55.1% last instar larva of 1st generation of CBW originated from C3 host plants. The larva from first instar to third instar of moths from C3 phenotype develop quicker compared with from C4 phenotype. However, larva from fourth instar to sixth instar from C3 phenotype developed slowly than C4 phenotype. The larva originated from C3 phenotype displayed lower survival rate at lower instar larva and higher survival rate at higher instar larva while compared to the C4 phenotype progeny. In the whole, quicker development for lower instar larva with lower survival rate, and slower development for large larva with higher survival rate occurred during their larval developmental process, However, total developmental duration and accumulative survival rate of larva as progeny of different phenotype CBW from C3 and C4 host plants were not significant. No significant difference of fitness of first generation of CBW from C3 or C4 was observed, indicating that the larva of CBW has adapted to this host plant variation. Generally speaking, the overwintering generation CBW, which originated from C3 or C4 host plants, as pupae, could overwinter successfully in North China, and provided equal quantity of moths in the next spring, therefore infested on the spring wheat, contributing comparative number of larva to the first generation CBW. On the other hand, spring wheat, as major host plant of first generation CBW in North China, could determine the larval developmental process through its nutrition component shift although their moth could come from C3 host plants or C4 host plants. Our research provided an effective and direct estimation of contribution by corn and cotton host plants to the overwintering generation and spring first generation CBW population in North China, and would be a key reference in making Bt management strategies to prevent local breakout of CBW.
