Ring-substituted dibenzoylhydrazines are well known as nonsteroidal ecdysone agonists that cause precocious larval molt leading to death. Among them, tebufenozide (RH-5992) is used in practice as insecticide to control lepidopteran pests selectively. Recently, a new dibenzoylhydrazine, methoxyfenozide (RH-2485), with a higher activity for Lepidoptera, has been discovered. To obtain insight into the molecular mechanisms involved in the insecticidal selectivity of the dibenzoylhydrazine family, we measured the in vivo toxicity of these dibenzoylhydrazines against larval stages of the beet armyworm, Spodoptera exigua, and their action on in vitro cultured imaginal discs. We found that both nonsteroidal ecdysone agonists induced premature and lethal molting, and caused the same effect as 20-hydroxyecdysone in vitro. Furthermore, we measured the larvicidal activity against S. exigua of a series of dibenzoylhydrazines, in which ring-substituents were varied in a range of halogen, lower alkyl, OCH 3 , SCH 3 , Ph, CN, NO 2 , and CF 3 . The substituent effects on the larvicidal activity against S. exigua were very similar to that for another lepidopteran insect species Chilo suppressalis, suggesting that the molecular mechanism of action of these compounds is similar within both lepidopteran species. Arch. Insect Biochem. Abbreviations used: EcR = ecdysone receptor; EC 50 = evagination of wing discs; IC 50 = hormone binding activity to wing discs; LD 50 = larvicidal toxicity; QSAR = quantitative structure-activity relationship; PonA = ponasteroneA; RH-5992 = tebufenozide; RH-2485 = methoxyfenozide; 20E = 20-hydroxyecdysone.

Both larvae and teratocytes liberated upon hatching from the eggs of the endoparasitoid Cardiochiles nigriceps Viereck were found to release proteins into their surrounding environment as they develop. Teratocytes were found to synthesize and release a number of proteins into culture media in which they were incubated. The proteins released differed among the different teratocyte ages. Larvae were also found to release proteins into the culture media in which they were incubated. Ligation of the head or anal vesicle altered the protein pattern found in the media. The results demonstrate that both larvae and the associated teratocytes release proteins that may have important functions in the parasitoidhost interaction. 0 1994 ~i~e y -~i s s , Inc.Key words: parasitoid, protein secretions, teratocytes, parasitoid larvae INTRODUCTIONInsects, following parasitism by parasitoid Hymenoptera, are either paralyzed or, if they grow and develop, the growth and developmental patterns are often altered. These pathologies, as discussed by Doutt [ 11, are not solely due to the physiological response of the host to the invader, but as discussed by Vinson and Iwantsch [2], are often due to factors released by the parasitoid that alter the physiology of the host in specific ways. Thus, the suitability of an insect to serve as a host for a particular parasitoid depends on constraints that the host represents [3] and the ability of the parasitoid to alter the physiological environment that the host represents. In some situations, and for some host processes, the developing parasitoid must conform to the physiological conditions of the host [4]. In other cases or for other processes in the same host, the parasitoid has evolved mechanisms that alter the host's immediate physiological environment [5-81. Acknowledgments: Approved as TA 30750 by the Director of the Texas Agricultural Experiment Station. Appreciation is extended to Zac Shawhan for insect colony maintenance.Received February 4, 1993; accepted April 6, 1993. 0 1994 Wiley-Liss, Inc. 198Vinson et al.Alteration of the physiological environment within which the parasitoid must develop involves both the injection and release of factors into the host [31. There are two basic sources of these factors. The first group is the parental derived factors that include the poison gland [9-111, calyx region of the lateral oviducts [12,13], the epithelium of the common oviduct [14], or the follicular epithelium [15,161. The second group is the progeny derived factors that include teratocytes and larvae that hatch from the egg [3]. Teratocytes are cells of the embryonic membrane of the parasitoid egg that are released upon hatching into the hemocoel of the host. The developing larvae are also a possible source of host regulatory factors.The larvae of Pimpla turionellae L. and ltoplectis conquisitor Say discharge secretions from their anus [24-271. These secretions have been reported to alter DOPA metabolism, and to have antibacterial and antifungal properties [24,27].Here we examin...

Ring‐substituted dibenzoylhydrazines are well known as nonsteroidal ecdysone agonists that cause precocious larval molt leading to death. Among them, tebufenozide (RH‐5992) is used in practice as insecticide to control lepidopteran pests selectively. Recently, a new dibenzoylhydrazine, methoxyfenozide (RH‐2485), with a higher activity for Lepidoptera, has been discovered. To obtain insight into the molecular mechanisms involved in the insecticidal selectivity of the dibenzoylhydrazine family, we measured the in vivo toxicity of these dibenzoylhydrazines against larval stages of the beet armyworm, Spodoptera exigua, and their action on in vitro cultured imaginal discs. We found that both nonsteroidal ecdysone agonists induced premature and lethal molting, and caused the same effect as 20‐hydroxyecdysone in vitro. Furthermore, we measured the larvicidal activity against S. exigua of a series of dibenzoylhydrazines, in which ring‐substituents were varied in a range of halogen, lower alkyl, OCH3, SCH3, Ph, CN, NO2, and CF3. The substituent effects on the larvicidal activity against S. exigua were very similar to that for another lepidopteran insect species Chilo suppressalis, suggesting that the molecular mechanism of action of these compounds is similar within both lepidopteran species. Arch. Insect Biochem. Physiol. 41:42–53, 1999. © 1999 Wiley‐Liss, Inc.

The present study was conducted to determine the effect of baits containing nano particles of silica against the fourth instar larvae of Agrotis ipsilon (Hufn.) along sequential daily intervals post treatment under laboratory conditions. The determined percentages of larval mortality due to the admixed baits with SiNPs increased up to 100% after 15 days of application. The admixing of nanoparticles of silica in the bait during the sensitive period of larval development caused morphological abnormalities that are generally irreversible and often lead to death, beside certain biochemical changes of some inorganic elements in the haemolymph of the treated insects. It could be concluded that the tested nanoparticles of silica were most effective and indicated the highest concentration reductions of inorganic constituents in larval haemolymph, especially calcium, sodium and potassium. Therefore, more attention must be directed towards the inorganic constituents in the larval haemolymph as biomarkers for SiNPs efficacy.

Laboratory studies were carried out in Egypt to examine the effects of treatment of the nymphs of Schistocerca gregaria during the later period of third instar with different dosages of gamma radiation ranging from 1000 to 3000 rad. The data indicate that treatment with a dose of 3000 rad induced complete mortality for all treated nymphs. However, irradiation with a dose of 2000 rad produced fourth instar nymphs which enter a state of suspended development for about 14 days. Exposure to a dose of 1000 rad induced three types of response associated with the endocrine activities. Some of the treated nymphs developed to the fifth instar with soft and thin cuticle without tanning or darkening, these nymphs did not survive more than a few hours after ecdysis. Other treated nymphs became fifth instar with anomalous wings and normal cuticle which survived about 18 days as permanent fifth instar nymphs before dying, while the rest of the treated nymphs moulted to permanent fourth instar which survived more than 1 month and eventually died. Corpora allata (CA) volumes in the permanent nymphs were estimated by planimeter method, revealing a pronounced reduction in their size in comparison with the untreated controls. It reflects a sharp inhibition in their synthetic activity of juvenile hormone (JH).We deduce that the permanent nymphs may be produced as a result of a direct inhibition on the cerebral neurosecretory cells of the brain, the source of stimulating factors for JH and ecdysone production. Gamma rays prevented the production of the tanning and darkening factor (Bursicon Hormone) in these cells.