Temperature-dependent development and survival of immature stages of the alfalfa leafcutter bee, Megachile rotundata (Hymenoptera: Megachilidae)

Abstract - Survival and development of eggs and larvae of the alfalfa leafcutter bee, Megachile rotundata, were determined for 9 constant temperatures ranging from 15-35 °C. Stage-specific survival of immatures was greatest at temperatures of 20-30 °C (> 75%) and high temperatures of 32 and 35 °C caused no greater mortality compared with that of 23-28 °C. When estimates of survival were combined over all stages (egg to prepupal formation) high mortality of 98.6 and 73.3% was calculated for low constant temperatures of 15 and 18 °C. At all other temperatures, combined survival for immature stages was high (> 70%). Completion of development was observed at all constant temperatures for the egg and 4 instar stages. Rate of development increased with increased temperature from 15 to 35 °C for the egg and first instar stages whereas for second, third and fourth instars, rate of development generally increased from 15 to 30 °C and then decreased from 32 to 35 °C. Frequency distributions of development times were constructed for each larval stage. A Weibull function provided a good fit to a single, temperature-independent distribution of normalized development times. Linear regression of development rate versus temperature provided an average base temperature of 15 °C and 116 degree-days to complete immature stage development.