Development and survival of Erigonidium graminicolum (Sundevall) (Araneae: Linyphiidae: Erigoninae) at constant temperatures

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Abstract
Development and survival of an erigonine spider, Erigonidium graminicolum (Sundevall) (Araneae: Linyphiidae), were studied at seven constant temperatures ranging from 15°C to 35°C. Plotting development rates (reciprocal of mean times for development) and survival rates (expressed as percentages) against the different constant temperatures indicated that E. graminicolum is well adapted to low temperatures, but sensitive to high temperatures. Juvenile development occurred over a wide range of constant temperatures, but the survival rate was low at the upper and lower extremes. All eggs died before hatching at the highest tested temperature (35°C). There were statistically significant differences between males and females in juvenile and pre-imaginal development times. Juvenile development time decreased as temperature was raised to 32°C, but increased at 35°C. The mean duration of pre-imaginal development (egg to adult) varied from 94.4 d at 15°C to 23.8 d at 32°C. Considering development rate and survival, the most favourable temperature range appeared to be 15–32°C. For all life stages, graphs obtained by plotting the reciprocal of development times against temperature could be described by the six-parameter rate function of Wang et al. (1982). Temperature-independent distributions of normalized development times were approximated by a cumulative Weibull function. Frequency distributions of development times changed with temperature; they were almost uniform at 15–20°C, more symmetrical at 25–28°C, and somewhat skewed to the right at 30–32°C. The sum of effective temperatures (SET), and lower development threshold (LOT), were established for all life stages of E. graminicolum. Survivorship curves varied with temperature and, on average, were Type III.