Development and survival of immature Aedes albopictus and Aedes triseriatus (Diptera: Culicidae) in the laboratory: effects of density, food, and competition on response to temperature.

Effects of food, density, and heterospecific interactions on temperature-dependent development of Aedes albopictus (Skuse) and Aedes triseriatus (Say) larvae and pupae were described using a degree-day model. Under all conditions, the predicted number of degree-days (DD(T0)) to complete larval development was less, and the threshold temperature (T0) for initiation of larval development was higher for Ae. albopictus than for Ae. triseriatus. The DD(T0) for both species was food and density dependent. However, the per capita food ration appeared to exert a greater influence on the developmental times of Ae. triseriatus immatures, whereas for Ae. albopictus effects of density were not completely eliminated by an increase in the per capita food ration. The presence of heterospecific larvae did not prolong the DD(T0) of either species. At the low food ration, DD(T0) for both species were significantly greater under conspecific conditions. The DD(T0) for Ae. triseriatus increased directly as the proportion of conspecific larvae increased. However, when a higher per capita food ration was provided, conspecific effects on DD(T0) were mitigated. For Ae. albopictus, estimated DD(T0) values for larvae reared in pure culture were significantly higher than when heterospecific larvae were present, regardless of the per capita amount of food provided. Survivorship of immatures was density and food-dependent for both species. Ae. albopictus exhibited higher immature survivorship under all conditions relative to Ae. triseriatus. For both species, survival probabilities were lowest under conditions of high density and low food. Addition of food improved survival for both species. The presence of heterospecific larvae exerted a differential effect on the survivorship response of Ae. albopictus immatures to temperature. Lowest probability of survival for Ae. albopictus was occurred at low temperature when the proportion of heterospecific larvae in containers was the highest. In contrast, at high temperatures, survivorship of immatures improved, but was lowest for pure species cultures. For Ae. triseriatus, survivorship of immatures was consistently lower for pure species cultures regardless of the temperature. Standing crop production of adults of both species was primarily food rather that density-dependent. Under field conditions, Ae. triseriatus were predicted to initiate development sooner and exhibit faster population growth early in the season than Ae. albopictus. However, because of the shorter DD(T0), Ae. albopictus population growth was predicted to surpass that of Ae. triseriatus populations later in the season. Based on optimal DD(T0) values from laboratory experiments, spring emergence dates of Ae. triseriatus females in western North Carolina for 1989 and 1990 were predicted from accumulated degree-days calculated from local air temperature records. Predicted emergence dates were congruent with results of a previous survey for the same locality, indicating that accumulated degree-days can be used to accurately predict the seasonal occurrence of Ae. triseriatus. The utility of the degree-day approach in predicting the phenology of Ae. albopictus remains to be established.