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

Authors: Reddy, Angelica; Pratt, Paul; HOPPER, JULIE - University Of California, Davis; CIBILS-STEWART, XIMENA - Instituto Nacional De Investigacion Argropecuaria, Urugary; CABRERA WALSH, GUILLERMO - Fuedei; MC KAY, FERNANDO - Fuedei

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2018
Publication Date: 9/26/2018
Citation: Reddy, A.M., Pratt, P.D., Hopper, J., Cibils-Stewart, X., Cabrera Walsh, G., Mc Kay, F. 2018. 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. 128:85-93. https://doi.org/10.1016/j.biocontrol.2018.09.016.
DOI: https://doi.org/10.1016/j.biocontrol.2018.09.016

Interpretive Summary: Classical biological control is the introduction of natural enemies (insects) to control exotic plants that have become invasive. Water hyacinth (Eichhornia crassipes) was introduced in the USA in 1884, and has become a serious pest in California. The weevil Neochetina eichhorniae was introduced in northern California in 1983 as a biological control agent. However, the abundance of this weevil is limited and water hyacinth remains a problem. A popular explanation for lack of control is that the weevil population struggles to increase because it is not cold-hardy enough to survive the cold winters of northern California. The purpose of this research is to identify a more cold-hardy weevil population that will be released in northern California to control water hyacinth abundance. We tested populations from northern California, Australia, South Africa, and Uruguay to examine the effects of low temperature on life-history performance of the weevil. We measured the development time, fecundity, survivorship, and thermal tolerance of individuals from the four populations under two temperature treatments simulating fall and winter seasons of northern California. Results show that the immature stages of all populations 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 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 (2.08 ± 0.22 eggs per day), twice that of the California population (0.95 ± 0.15 eggs per day). Therefore, the introduction of N. eichhorniae from Australia into northern California may increase weevil densities, distribution, and improve biological control of water hyacinth.

Technical Abstract: 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 among 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 traits. Interestingly, 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 (2.08 ± 0.22 eggs per day), twice that of the California population (0.95 ± 0.15 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.