Temperature-dependent development, survival, and potential distribution of Ischnodemus variegatus (Hemiptera: Blissidae), a herbivore of West Indian marsh grass.
The bug Ischnodemus variegatus (Signoret) (Hemiptera: Blissidae) is an adventive herbivore, native to South America that feeds in the invasive grass Hymenachne amplexicaulis (Rudge) Nees (Poaceae). This grass is a problematic weed in Florida and Australia, but it is a highly valued forage in Mexico, Cuba, and Venezuela. We studied the influence of nine constant temperatures (8-38°C) on the developmental time and survival of I. variegatus. Complete egg and nymphal mortality occurred at temperatures ≤20.5°C and at 38°C. Developmental time decreased linearly with temperature until 28-30°C and then increased at 33°C. Mortality of first, second, and third instars was high across all temperatures. Developmental time across all temperatures was greatest for eggs, first and fifth instars compared with other stages. Linear and Brière-1 nonlinear models were used to determine the lower temperature threshold at which the developmental rate (1/D) approached zero. The lower thresholds to complete development (egg to adult) estimated with the linear and nonlinear model were 14.6 and 17.4°C, respectively. The total degree-days required to complete development estimated by the linear model was 588. Using temperature data from Florida, a map was generated to project a prediction grid of I. variegatus generations per yr. Based on these predictions, the insect can complete three to five generations per year in areas currently invaded in Florida. Results of this study will be used to understand the potential distribution and population growth of I. variegatus in H. amplexicaulis infested regions.