Temperature and moisture effects on the success of egg hatch in Trirhabda geminata (Coleoptera: Chrysomelidae)

Eggs of Trirhabda geminata (Hem) were subjected to several constant temperatures (15, 22, 25, and 30 degrees C) and moisture (wet or dry for varying lengths of time) regimens. Upon wetting, eggs changed color (from brown to yellow-orange) and swelled from 1.07 by 0.64 to 1.14 by 0.72 mm (length by width). Warmer temperatures shortened embryonic development time for eggs held wet. Eggs that were continuously held dry did not develop. A chilling requirement or diapause was not required for successful hatch. Optimal temperature for egg survival (98%) was 25 degrees C. Some eggs hatched at all temperature regimens as long as they were in contact with a moisture source. The longer the period that eggs were held dry, however, the greater the decrease in survivorship. Approximately 10% of eggs held dry for extended periods (322 d) are still able to hatch when moistened. Our results indicate that moisture is required for egg development and is likely used as a proximal stimulus by T. geminata for the availability of its host plant.