The 4-isobutyl (iBMOS) and 5-phenyl (5-PMOS) derivatives of 1,3,2-oxazaphospholidine 2-sulfide suppressed the larval growth, pupation, and emergence of Tribolium castaneum and Musca domestica. Feeding larvae iBMOS or 5-PMOS for 2 days reduced weight gain, suppressed soluble gut trehalase activity, and increased whole body levels of cyclic adenosine 3′,5′-monophosphate (cAMP) relative to control. Invertase was slightly suppressed and neither amylase nor protease was affected in vivo by these phosphorus compounds. At a concentration of 10-4 M, iBMOS and 5-PMOS had no direct effect on these enzymes in vitro. At a dose needed for 50% mortality (LD50) 20 hr after topical application, 5-PMOS caused a 50% inhibition of M. domestica adult females acetylcholinesterase activity (AChE), 60 min after topical application. T. castaneum larvae fed for 24 hr on a diet containing 80 to 320 ppm iBMOS underwent AChE inhibition of 61 to 86%; cAMP content was increased up to 186% and mortality up to 34%, relative to control. Similar phenomena were observed with 80 to 320 ppm of 5-PMOS. It can be concluded that at sublethal concentrations, these compounds reduced trehalase activity, which is important for energy supply in insects, whereas at lethal concentrations they inhibited AChE activity similar to other acyclic phosphorus compounds.
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