Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Wildland Resources

Department name when degree awarded


Committee Chair(s)

William A . Brindley


William A . Brindley


G. E. Bohart


D. W. Davis


D. V. Sisson


J. C. Street


The alfalfa leafcutter bee, Megachile rotundata, one of the most important pollinators of alfalfa, generally became more susceptible to carbaryl as the adults aged. LD50 values for carbaryl toxicity were 240,166, 109, and 51 μg carbaryl/gram for the 1, 2, 3, and 4 days-old adult male bees. For the female bees, these were 245 , 551, 289, and 262 μg car-baryl/ gram. Lipid content and microsomal enzyme activity (measured by EPN detoxication in vitro) decreased in both sexes as the bees aged.

Synergist ratios, defined as the ratio of the LD50 of carbaryl alone to the LD50 of carbaryl applied after the synergist piperonyl butoxide, were measured. These did not correlate with either decreasing LD50 values or decreasing EPN detoxication in the males being 12, 21, 42, and 53 for the 1, 2, 3, and 4-day-old bees. In female bees the synergist ratio corresponded more closely being 23 , 49 , 11, and 15 as the females aged from 1 to 4 days. Published literature has suggested that such synergist ratios are usable as in vitro estimates of detoxication ability, higher values indicating more detoxication potential, but there may be difficulties in the proper estimation of the synergist ratio.

The use of enzyme-inducing drugs for protection of the bees from carbaryl poisoning was studied. Among the three drugs used, only chlorcyclizine increased the LD50 value (to about two fold) in the 4-day-old male. Aminopyrine increased the male's susceptibility to carbaryl while phenobarbital had no effect at all . None of the drugs significantly changed the female's susceptibility to carbaryl except aminopyrine which lowered the LD50 from about 262 to 75 μg / gr. Studies with in vitro EPN detoxication indicated that all three drugs caused increases in microsomal enzyme activity up to four or five fold and decreases in lipid content of about 20 to 30%.



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