Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)



Committee Chair(s)

Ting H. Hsiao


Ting H. Hsiao


Frank Parker


George Bohart


Ivan G. Palmblad


Raymond T. Sanders


The effects of photoperiod and temperature on diapause induction in the alfalfa leafcutter bee, Megachile pacifica (Panzer) (=M. rotundata Auct.), were studied during the summers of 1972, 1973 and 1974, The influence of photoperiod and temperature on mortality, rate of development and incidence of diapause was measured during the developmental stages of this insect. The aim of this research was to assess the potential for manipulation of the number of generations of this bee per season so as to develop a practical and ecologically-sound method of management,

Eggs, larvae, pupae and adults of M. pacifica were subjected to regimens of temperatures of 5, 10, 14, 16.5, 20, 21, 25, 26.5 and 30°c and photoperiods of 0, 8 and 16 hours of light, Experiments conducted during 1972 and 1973 involved treating eggs and larvae directly to deter-mine whether diapause was induced in the immature stages, No difference was found between the test and control groups, Experiments of 1973 and 1974 involving treatment of either pupae or adults were designed to determine if inducement of diapause was maternal, Treated adults were released, their progeny were collected and reared to check for percent pupation. These experiments on the adults failed to show any difference between the experimental and control groups in percentage of diapause.

Treatment of the pupal stage was conducted in 1974 by subjecting stages from the dark pupa to pre-emerged adult to a temperature of 10° C for 3 hours daily for 8 consecutive days. This low-temperature treatment proved to be most effective in inducing diapause, resulting in 96 percent diapause as compared to 60 percent for the control group.

The findings indicate that diapause in M. pacifica is maternally induced and that the possibility of developing a practical method for producing either univoltine or bivoltine generations per season is promising. Recommendations are given for better management of M. pacifica.



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