Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2005
Publication Date: 12/1/2005
Citation: Herrera, A.M., Dahlsten, D.D., Tomic-Carruthers, N., Carruthers, R.I. 2005. Estimating temperature-dependent developmental rates of diorhabda elongata (coleoptera: chrysomelidae), a biological control agent of saltcedar (tamarix, spp.). Environmental Entomology. 34(4):775-784. Interpretive Summary: Saltcedar (Tamarix spp.) is an exotic and invasive shrub introduced to the western United States in the early 1800's as an ornamental and to prevent stream bank and wind erosion. The plant, however, it is now considered a pest in riparian areas where it out competes and replaces native vegetation. As a result of saltcedar invasions, populations of riparian wildlife such as birds, rodents, and fish may have significantly declined. To aid in the management of this invasive shrub, an Asian leaf beetle, Diorhabda elongata Brullé (Coleoptera: Chrysomelidae) was released in 2001 in the western United States for the biological control of saltcedars. Our studies focused on the developmental biology of this agent. Developmental and survival rates of all the immature beetle stages were studied in the laboratory at six constant temperatures ranging from 15 to 40ºC. Then, linear and non-linear mathematical models were fit to the developmental data to determine lower developmental thresholds for all stages. These models can also be used to estimate developmental rates at temperatures not included in the study. Thus, the accuracy of each model type in estimating beetle development over the entire range of temperatures used in this study was assessed and compared. Our analysis indicated that the Logan type III non-linear model was a better predictor of D. elongata developmental rates than the other models. Results from this study were used optimize the effectiveness of D. elongata as a biological control agent by 1) enhancing the efficiency of mass-rearing methods for open field releases of D. elongata in California and 2) incorporating the Logan type III developmental model into an insect population model that is being used to predict D. elongata population density and survival in the field.
Technical Abstract: Developmental times and survival rates of the immature stages of Diorhabda elongata Brullé (Coleoptera: Chrysomelidae), a biological control agent of saltcedar (Tamarix spp.), were studied in the laboratory at six constant temperatures (15 to 40ºC). At 15ºC and 40ºC, eggs did not develop and sustained 100% mortality. Similarly, larvae in 15ºC and pupae in 40ºC did not develop and sustained 100% mortality. For all three larval stages, the developmental time decreased with increasing temperature between 20 and 35ºC and increased at 40ºC. Developmental times also decreased with increasing temperature between 20 and 35ºC for the pupal stage as did total developmental time from egg to adult. Both linear and non-linear models were used to describe the relationship between developmental rates (1/d), and temperature (ºC) and to determine stage-specific lower and upper developmental thresholds, respectively. The lower developmental thresholds, calculated using the linear model, ranged from 6 to 15ºC for all life stages. Using the non-linear model, the lower developmental thresholds ranged from 15 to 18ºC for all life stages. Likewise, the high temperature thresholds for the first, second, and third instar larvae, pupae and total development were ranged between 40 to 42ºC. Results from this study were used to enhance the efficiency of mass-rearing methods for open field releases of D. elongata in California. More importantly, this study is the first step in the construction of a detailed population simulation model to predict field phenology and density of D. elongata to further optimize the use of this biological control agent in managing saltcedar in the western U.S.