Action and pharmacokinetics of a novel insect growth regulator,halofenozide, in adult beetles of Aubeonymus mariaefranciscae and Leptinotarsa decemlineata

Topical application of halofenozide on adults of the Colorado potato beetle (CPB), Leptinotarsa decemlineata, and Aubeonymus mariaefranciscae (AMF) exhibited its effects in a different way in the two coleopterans. In CPB, the fecundity was strongly affected, whereas the main effect in AMF was a drastic decrease of the progeny survival. The rate of penetration of labeled halofenozide through the cuticle followed a similar pattern in CPB and AMF, whereas the rate of excretion was much more rapid in AMF. The extremely slow excretion of the product in CPB suggested that this fact must contribute to the prolonged action of halofenozide on fecundity at its highest dose of 20 μg per adult. Retention of halofenozide in the reproductive system of males of AMF and CPB was low, whereas high levels of radioactivity were recovered in females (ovaries + eggs). Comparing females of both coleopterans, CBP retained a higher amount than AMF. Moreover, treated CPB adults showed a rapid cessation of oviposition due to distorted ovaries, detrimental oocyte growth, and loss of oviposition due to the fact that yolk protein synthesis and/or incorporation into eggs was reduced. In AMF, the development of the progeny was strongly affected, and more than 80% of first‐instar larvae died after egg hatching in the first 25 days after the treatment, due to premature molting and inhibition of ecdysis. Cross sections of intoxicated first larval instars of AMF originating from adults that were topically treated with halofenozide showed the presence of a double cuticle and these larvae could not shed the old cuticle. Arch. Insect Biochem. Physiol. 41:201–213, 1999. © 1999 Wiley‐Liss, Inc.     

Significance of absorption, oxidation, and binding to toxicity of four ecdysone agonists in multi-resistant cotton leafworm

Treatment of last-instar larvae of multi-resistant cotton leafworm Spodoptera littoralis with four dibenzoylhydrazines, methoxyfenozide (RH-2485), tebufenozide (RH-5992), halofenozide (RH-0345), and RH-5849, resulted in premature molting leading to death. Methoxyfenozide was the most toxic followed by tebufenozide, halofenozide, and RH-5849. To explain differences in toxicity, especially between multi-resistant and laboratory strains, absorption in the body tissues and oxidative metabolism were tested with 14C-labeled ecdysone agonist and a Lineweaver-Burk assay, respectively. Then to address different compound potencies in multi-resistant strains, the potency of the four ecdysone agonists was measured based on their ability to mimic the natural insect molting hormone, 20-hydroxyecdysone (20E) by inducing evagination in isolated imaginal wing discs. Using monoclonal antibody 9B9, the presence of ecdysteroid receptors in imaginal discs in vitro was confirmed. In parallel, Scatchard plot analysis with whole imaginal wing discs cultured with different concentrations of 3H-labeled ponasterone A indicated no significant difference in affinity and in number of target sites for binding between multi-resistant and susceptible laboratory strains. The four compounds tested caused the effect as agonists of 20E in vitro, and typically the order of their toxicities (LC50s) corresponded with that for evagination-induction with whole imaginal discs.     

Toxicity of two ecdysone agonists, halofenozide and methoxyfenozide, against the multicoloured Asian lady beetle Harmonia axyridis (Col., Coccinellidae)

Abstract: The insecticidal activity of two ecdysone agonists, methoxyfenozide (RH-2485) and halofenozide (RH-0345), was tested against last-instar larvae of the natural predator Harmonia axyridis (Col., Coccinellidae). In addition, the relative weight gain of the larvae after application was followed. Both products proved to be equally toxic at concentrations of 25, 50 and 100 mg/l. The ecdysteroidal activity of the compounds caused premature induction of larval moulting, cessation of feeding and incomplete pupation in affected larvae. Although, compared with previous results with methoxyfenozide and halofenozide in target pests such as the Colorado potato beetle, Leptinotarsa decemlineata , these compounds caused mortality only after application at relatively high concentrations.