The effect of temperature on weevil development

Insect development rates are strongly related to temperature. In general, development only occurs at temperatures above a minimum threshold and development rates increase proportionally to temperature to some optimum level, above which development rates and survival decline dramatically (Wagner et al. 1984). These relationships are often interpreted as a constant heat accumulation (degree days) that is required for development (degrees above threshold * days to develop). Empirically deriving the temperature-development relationship for a species allows understanding of how temperature may limit the growth of a population by limiting the number of generations per year. Furthermore, survival and egg production may vary with temperature. Mazzei et al. (1999) determined the temperature-development relationship (See Figure 1, below) for the milfoil weevil and analyzed changes in survival rates and damage to milfoil at different temperatures. These development rates can be combined with lake temperature data (Figure 2 below) to predict potential weevil population development. Development from egg to adult takes from 17 days at 29 C to 62 days at 15 C (see table for more details).

Summary of temperature effects on weevil development (from Mazzei et al. 1999):

• Development rate increased linearly above a threshold of 10 degrees C, with a maximaum at about 29 degrees C.
• The rate of stem damage increased at higher temperatures, but the amount of damage inflicted by an individual weevil during its development (10 cm of stem) did not differ across temperature treatments.
• Overwintering females may require 6-9 days above 15 degrees at the beginning of the growing season to develop eggs.

Figure 1: Temperature-development relationship for the milfoil weevil. From Mazzei et al. (1999).