Variation in cool temperature performance between populations of Neochetina eichhorniae (Coleoptera: Curculionidae) and implications for the biological control of water hyacinth, Eichhornia crassipes, in a temperate climate

Biological control of water hyacinth, Eichhornia crassipes, has resulted in variable outcomes in temperate regions where cool climates are thought to limit population growth and performance of the biological control agents. The weevil, Neochetina eichhorniae (Coleoptera: Curculionidae), originating from Argentina, was introduced into northern California, USA, in 1982. The realized distribution and abundance of this weevil is limited, and the exotic weed remains a problem. In this study, we tested populations of N. eichhorniae from northern California, Australia, South Africa, and Uruguay to examine the effects of low temperature on life-history performance to determine if cold hardiness differs between populations. We measured the development time, fecundity, survivorship, and thermal tolerance (chill coma: CTmin and supercooling point SCP) of the four N. eichhorniae populations under two temperature treatments simulating fall and winter seasons of northern California. Results suggest that immature stages of all populations tested failed to survive and females did not reproduce in the winter treatment. In the fall treatment, all populations showed similar performance in most of the measured life history traits. The Australian population had the highest intrinsic rate of increase, net reproductive rate and doubling time, due to its longer oviposition period, and higher daily fecundity (2.1 +/- 0.2 eggs per day), twice that of the California population (1.0 +/- 0.2 eggs per day). Thus, the introduction of N. eichhorniae from Australia into northern California may increase weevil densities, distribution, and improve biological control of water hyacinth.