Temperature-dependent effects on development, mortality, and growth of Hippodamia convergens (Coleoptera: Coccinellidae)

Insect natural enemies selected for specific traits such as faster developmental times, higher survivorship, increased fecundity, and larger body size might be considered during production of biological control agents in certain situations. For instance, traits related to developmental rates may be selected for if genetically based variation exists within temperature-dependent responses. We compared preimaginal development, mortality, and size of Hippidamia convergens Guerin-Meneville at 4 constant temperatures (18, 22, 26, and 30 degrees C). Total preimaginal development ranged from 51 d at 18 degrees C to 14 d at 30 degrees C. Developmental times were significantly different among isofemale lines of field-collected II. converges from Oregon at all temperatures tested (18, 22, 26, and 30 degrees C). Variation within female lines was significant only at 26 degrees C. The lower developmental thresholds for egg, larval, and pupal stages were 9.9, 13.7, and 14.5 degrees C, respectively. Degree-day (DD) requirements for development were 58.8, 166.7, and 52.6 for eggs, larvae, and pupae, respectively. Total preimaginal development required 231 DD above a temperature threshold of 13.6 degrees C. Degree-day requirements for 14 field-collected female lines varied from 223 to 273, whereas the lower threshold for development ranged from 13.1 to 13.8 degrees C. Mortality decreased with increasing temperatures. At the lower temperature (18 degrees C), higher mortality occurred during the 4th instar and pupa. Pupal and adult weights differed across temperatures. Heavier pupae and adult beetles were reared at 22 degrees C. Also, wings were larger among beetles reared at 22 degrees C. The development, mortality, and size measurements provide data for establishing suitable rearing conditions for future studies on the ecology of H, convergens.