Julius J. Menn

Endocrine Regulation of Pheromone Production in Lepidoptera

Publisher Summary This chapter discusses endocrine regulation of pheromone production in Lepidoptera. In insects, pheromonal communication may be regulated by the neuroendocrine systems in the producer of the signal, the receiver, or both. Thus, hormones and/or neurotransmitters may regulate the biosynthesis or release of the pheromone and may also mediate the response to the pheromone. Among Lepidoptera, reproductive activity is probably never distributed evenly over a day but instead peaks at or is restricted to a few hours during the photophase or scotophase. The timing for the female of a species to release the sex pheromone has coevolved with male flight activity and maximal responsiveness to pheromonal signals. Such a coordination of mating activity provides the species with a high probability of mate finding and reproductive isolation. In nocturnal species of moths, reproductive activity is usually gated and follows an endogenous rhythm that is modified by environmental cues. Circadian endogenous rhythms of pheromone production and calling behavior have been reported in several species of moths.

Elucidating mechanisms of tobacco budworm resistance to allelochemicals by dietary tests with insecticide synergists

Abstract Three major cotton ( Gossypium hirsutum L.) plant allelochemicals—gossypol, a mixture of condensed tannins, and isoquercitrin—were fed to 1-, 3-, and 5-day-old tobacco budworm ( Heliothis virescens Fab.) larvae at the 0.06% level with and without 0.02, 0.06, and 0.60% piperonyl butoxide, an insecticide synergist that inhibits the activity of an insects existing detoxifying enzymes. All three allelochemicals were toxic to the 1- and 3-day-old larvae, but they were not toxic or were only marginally toxic to the 5-day-old insects. Piperonyl butoxide was toxic to the 1-, 3-, and 5-day-old insects, although less so to the 5-day-old insects. With both the allelochemicals and piperonyl butoxide in the diet, further decreases of growth were observed. Seven additional synergists representing several classes of compounds known to inhibit mixed function oxidases (MFOs; polysubstrate macrooxygenases, PSMOs) or esterases in the insect were also added to the diet at the 0.02 and 0.06% levels, with and without allelochemicals at the 0.06% level. However, only piperonyl butoxide decreased the growth rate of 5-day larvae fed the three allelochemicals. Thus, one effect of gossypol and other allelochemicals on insect feeding can be inferred to be toxicity, but gossypol may also act as an antifeedant.

Dyfonate metabolism studies: II. Metabolic pathway of O-ethyl S-phenyl ethylphosphonodithioate in rats

Abstract Dyfonate (O-ethyl S-phenyl ethylphosphonodithioate) is rapidly metabolized in living rats to form polar products which are excreted in the urine and in the feces via the bile. The identified metabolites account for more than 94% and 78% of the administered dose from both the phosphorus- and thiophenol-containing moieties, respectively. The metabolic pathway found for Dyfonate in rats is similar to that previously established in plants. The terminal residues are O-ethyl ethane phosphonothioic and -phosphonic acids, and O-conjugates of 3- and 4-(hydroxyphenyl) methyl sulfone. Dyfonate-oxon is the intermediate in formation of O-ethyl ethane phosphonic acid, as the phosphonothioic acid is not desulfurated in vivo. The oxon is formed in the rat liver microsome-NADPH2 system, but in vivo, it appears to undergo rapid hydrolysis.

Dyfonate metabolism studies: I. Absorption, distribution, and excretion of O-ethyl S-phenyl ethylphosphonodithioate in rats

Abstract The rate and extent of elimination of Dyfonate ( O -ethyl S -phenyl ethylphosphonodithioate) residues in rats has been determined using radioactive preparations of Dyfonate labeled in the phosphonic acid and thiophenyl portions of the molecule. Dyfonate and/or its metabolic products are rapidly excreted from the rat, after oral or intraperitoneal dosing, primarily in the urine and to a lesser extent in bile and feces. An average of 97.8% of the administered radiolabeled dose was recovered 96 hr after dosing. Only trace radioactive residues were found in animal tissues and organs, and these were transient in nature. Conditioning with Dyfonate showed that animals eliminate Dyfonate residues essentially at the same rate with or without conditioning. The cannulation experiment demonstrated the importance of biliary excretion as a route of residue elimination. No significant alteration in the excretion pattern of Dyfonate residues was detected as a result of oral or intraperitoneal administration of the insecticide.

New aspects of organophosphorus pesticides. IV. Newer aspects of the metabolism of phosphonate insecticides

Organophosphorus (OP) compounds comprise an increasingly important class of insecticides owing to the greater emphasis on use of more selective and biodegradable chemicals for management of insect pest populations. There are available at present approximately 85 commercial and experimental OP insecticide chemicals (Kenaga and Allison 1969) including several phosphonate esters (OP compounds with a P—C bond).

Inhibition of juvenile hormone biosynthesis in the tobacco hornworm, Manduca sexta, by a bisthiolcarbamate juvenoid and related compounds

Abstract Biosynthesis of juvenile hormone in the tobacco hornworm, Manduca sexta , is inhibited by the bisthiolcarbamate juvenoid N -ethyl-1,2-bis(isobutylthiolcarbamoyl)ethane both in vitro and in vivo . In vitro an extremely steep dose-response curve was obtained with an ID 50 value of 6 × 10 −6 M . However, in vivo topical treatment with the compound resulted in mild JH antagonistic symptoms, suggesting rapid metabolism of the compound. In agreement with results from metabolic studies performed on plants and in mammals, sulfoxidation of the thiocarbamate S -(4-chlorobenzyl) N,N -diethylthiocarbamate resulted in an enhanced inhibitory effect on JH biosynthesis in vitro . This suggests that the corresponding thiocarbamate sulfoxides may act as intermediates in carbomylating critical thiol sites important in the terpenoid biosynthesis pathway. Furthermore, this study shows that these prototype compounds are interesting tools for further investigation of chemical inhibition of JH biosynthesis in insects.

Prospects and status for development of novel chemicals for IPM in cotton

Abstract Increasing concerns regarding food and feed safety, quality of groundwater and surface water, and resistance of insects to chemical pesticides, have provided added impetus to the development of integrated pest management (IPM) systems for cotton. The chemical industry is cognizant of these concerns and is directing increasing research resources to develop more selective, IPM-compatible pesticides through more rational approaches than those used previously. This paper discusses the status of current chemical control practices in cotton and describes several promising candidate control agents that could be compatible with IPM. The developing use of semiochemicals for insect control is also briefly discussed in terms of the potential of the IPM approach to reduce the application volume and frequency of conventional insecticides.