Author
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Oberlander, Herbert |
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Silhacek, Don |
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Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/2/1998 Publication Date: N/A Citation: N/A Interpretive Summary: As a result of the development of resistance to insecticides by stored product insects and the limitations on the use of fumigants due to regulatory and environmental considerations, there is a continuing interest in the evaluation of Insect Growth Regulators as protectants for stored commodities. Juvenile hormone mimics have been investigated most thoroughly in this regard and combine the advantages of low mammalian toxicity, target specificity, and compatibility with other chemical and biological treatments. During the past decade, a new class of insect growth regulators has become available with the discovery that a series of non-steroidal compounds act as agonists of the natural insect molting hormone, 20- hydroxyecdysone. Despite the substantial work with agricultural applications of ecdysteroid mimics to field crop pests, there has been little attention paid to the actions of these types of compounds on stored product insects. Research by scientists at the Center for Medical, Agricultural and Veterinary Entomology, ARS, USDA, in Gainesville, Florida demonstrated that inclusion of a juvenile hormone mimic with treatment with a non-steroidal ecdysteroid mimic prevented the reduction in weight gain that would otherwise have been caused, but increased mortality of the larvae. One strategy to combat resistance of insects to insecticides is to employ combinations of chemicals with different modes of action . These results point to the possible utility of combining Insect Growth Regulators that mimic both juvenile hormone and ecdysteroids for greater long-term effectiveness in controlling insect pests. Technical Abstract: The influence of non-steroidal ecdysteroid agonists on Indianmeal moth larvae was assessed by rearing last instar larvae on diet treated with RH-5992 (tebufenozide) or RH-2485. Larvae were monitored for effects of the ecdysteroid agonists on weight, metamorphosis and mortality. Larvae treated with either of the ecdysteroid agonists at a concentration of 5 ppm or higher gained less weight and had greater mortality than did larvae reared on control diet. The JH mimics prevented adult emergence, and the larvae continued to feed throughout the month-long observation period. However, larvae treated with a juvenile hormone mimic gained weight despite the presence of an ecdysteroid agonist in the diet. On diets treated with 0.1 ppm of RH-2485 or RH-5992, JH-treated larvae gained even more weight than did untreated controls. Although the addition of a JH mimic to ecdysteroid treated diet resulted in increased weight, it did not lead to reduced mortality. In fact, combinations of a JH mimic with 10 ppm RH 2485 or RH 5992 resulted in nearly 100% mortality compared with 40-70% mortality without the JH compounds. These results indicate that JH mimics not only overcome the inhibitory effects of ecdysteroid agonists on weight gain, but they also resulted in increased mortality compared with moderate doses of ecdysteroid agonists alone. |
