Developmental Biology of Dictyna Spp. (Araneae: Dictynidae) in the Laboratory and Field

Abstract

The developmental biology of two cribellate spider species, Dictyna coloradensis and D. major, was studied in the laboratory (D. coloradensis) and in the field (both species). Laboratory-reared D. coloradensis matured after 6-10 molts and spent an average of 8-13 days per stadium prior to the sixth stadium. Males required an average of 160 days to reach maturity whereas females required 220 days. Mean carapace widths differed among instars, although their ranges overlapped considerably. Field observations revealed univoltine life cycles for both species, with subadults overwintering and maturing in late spring. Although size of overwintering individuals was similar at the northern and the one southern site (significantly smaller-sized individuals at the other southern site were attributed to mortality of larger individuals due to pesticide drift), Dictyna coloradensis females were significantly larger at the southern, longer-season sites [3000 growing degree days (GDD)] than at the northern, shorter-season site (1500 GDD). Females were largest when reared in the laboratory compared with all field sites. Spiderling field data suggest that development may be arrested at the southern site, synchronizing the population and producing similar-sized overwintering individuals. When reared in the laboratory under the same conditions, however, individuals from both the northern and southern sites developed at the same rate and attained the same adult size.