Performance of the biological control agent flea beetle Agasicles hygrophila (Coleoptera: Chrysomelidae), on two plant species Alternanthera philoxeroides (alligatorweed) and A. sessilis (joyweed)

Agasicles hygrophila has been used as a biological control agent on invasive alligatorweed, Alternanthera philoxeroides in China. We conducted tests to determine the impact of A. hygrophila on the non-target species A. sessilis and examined the developmental differences of A. hygrophila raised on these two plant species to assess the ecological and environmental safety of the introduced A. hygrophila in China. No significant differences were detected in the developmental timing of A. hygrophila from larvae to adults, in larval hatching, and in pupal fresh weight in three treatments: A. hygrophila reared on A. philoxeroides through all life stages; A. hygrophila larvae reared on A. sessilis but pupated in the stems of A. philoxeroides; and A. hygrophila reared on A. sessilis through all life stages. However, when A. hygrophila larvae were reared on A. sessilis but pupated in the stems of A. philoxeroides, they had a significantly longer preoviposition period, lower pupation rate, and lower fecundity than those in other two treatments. The demographic parameters examined indicated that lower fecundity (GRR, R0) and intrinsic rate of natural increase (rm = 0.06), but longer doubling time (Td) were found in A. hygrophila larvae reared on A. sessilis but pupated in the stems of A. philoxeroides compared to the other two treatments (rm = 0.11). Ultimately, A. hygrophila has limited effects on the non-target A. sessilis and is considered safe to the ecosystem. Moreover, A. sessilis would provide a marginally suitable host for A. hygrophila in regions where the two species intermingle.