In vivo effect of ACE inhibiting in mealworms on ovarian composition and ecdysteroid amounts.

Captopril is an inhibitor of angiotensin converting enzyme (ACE) used against arterial hypertension in mammals. The aim of this study was to evaluate captopril in the mealworm Tenebio molitor (Coleoptera: Tenebrionidae). The drug was diluted in acetone and administered topically (10 microg/3microl) on newly emerged adult females. The biochemical composition (proteins, lipids, carbohydrates, nucleic acids) and the ecdysteroid amounts of ovaries were determined at day 4 following treatment corresponding to the end of the vitellogenesis process. Biochemical analyses revealed that captopril applied in vivo reduced both total protein, lipid and carbohydrate amounts of ovaries, respectively. In addition, measurement of ecdysteroids by an enzyme-immunoassay indicated a significant decrease in ovarian ecdysteroid amounts. As a consequence, the reduction of reproductive capacity is possibly related to ecdysteroid production. Further experiments are needed to determine the action mechanism of captopril and the functions of ACE in insects.

Comparative toxicity of three ecdysone agonist insecticides against the Mediterranean flour moth.

The Mediterranean flour moth, Ephestia Kuehniella Zeller (Lepidoptera: Pyralidae), is an important pest in stored products worldwide, and is one of the major pests in flour mills in Algeria. Because environmental consideration, alternative approaches to neurotoxic insecticides, as well as safe, effective, and sound integrated pest management strategies are developed pest control agents such as the insect growth regulator (IGRs). Among these IGRs, the bisacylhydrazine derivatives are nonsteroidal ecdysterold agonists that mimic the action of moulting hormones and induce a precocious and incomplete moult in several insect orders. In topical bioassays using the pupae of E. kuehniella, three ecdysteroid agonists: RH-5849, the first bisaclhydrazine ecdysone agonist and two analogs, RH-5992 (tebufenozide) and RH-0345 (halofenozide), were evaluated on the reproduction under laboratory conditions. In a first series of experiments, the efficacy of these compounds was tested. These compounds exhibited insecticidal activity and the duration of pupal development was reduced with a dose-response relationship. Among the three tested compounds, tebufenozide (LD50 = 0.005 microg) appeared the most potent ecdysteroid agonist against E. kuehniella (RH-5849: LD50 = 0.05 microg and RH-0345: LD50 = 5.10 microg). In a second series of experiments, the effects of the ecdysone agonists (LD50) were investigated on the reproduction. Data showed that the three compounds affected growth of ovaries as evidenced by morphometric measurements of the ovaries from newly emerged adult females. In addition, the thickness of the chorion from basal oocytes was reduced only by RH-5992 and RH-0345. However, electron microscopic observations revealed that the three compounds had no significant effect on the fine structure of chorion. Finally, measurements of ovarian ecdysteroids' production by an enzyme immunoassay showed an increase in the hormonal amounts recorded in treated series compared to control series.

Effects of flucycloxuron, a chitin synthesis inhibitor, on reproductive events and thickness of chorion in mealworms.

Flucycloxuron (FCX), a benzoylphenylurea derivative, was evaluated on Tenebrio molitor. The compound was incorporated into the diet and administrated to newly emerged females at various doses (2, 5 and 10 mg/kg). FCX was found to affect several reproductive events such as the duration of preovipostion and oviposition period, the fecundity, the viability of eggs and the duration of embryonic development, respectively. Morphological study of ovaries showed that FCX reduced both oocytes number, the ovaries weight and the size and the volume of the basal oocyte during the sexual maturation. In addition, it reduced the thickness of chorion from freshly laid eggs. However, electron microscopic study revealed that this compound had no significant effect on the fine structure of chorion. Finally, measurements of ovarian ecdysteroids production by an enzyme immunoassay indicated a reduction in the hormonal amounts recorded.

Comparative effects of some ecdysteroid agonists in mealworms: ecdysteroid amounts and protein analysis in developing ovaries under in vivo conditions.

Some ecdysteroid agonists (RH-0345, RH-5849, RH-5992) were tested topically (10 microg/female) on newly emerged adult females of mealworms under in vivo conditions. In a first series of experiments the compounds were assayed on ovarian ecdysteroid production measured at day 2 and 4 following treatment, corresponding to the beginning and the end of vitellogenesis. All tested compounds resulted in a significant increase in ovarian ecdysteroid amounts. RH-5992 and RH-0345 were more active than RH-5849. In a second series of experiments, the activity of the compounds was investigated on ovarian proteins. The ecdysteroid agonists caused a significant reduction of protein amounts in the ovaries, and electrophoretic separation of ovary extracts from treated series showed that one or two bands were missing. These observations may an interference with the vitellogenesis process.

RH-0345 restored partly the effects induced by KK-42 on reproductive events in mealworms.

In the mealworm, Tenebrio molitor L., KK-42, an imidazole derivative, was found to reduce ovarian ecdysteroid production, while RH-0345, a benzoylhydrazine analogue, has been reported to affect growth and development of mealworm ovaries in a manner similar to 20-hydroxyecdysone. In order to determine whether the reduction of reproduction events is dependent on inhibition of ecdysteroid production by ovaries, RH-0345 (10 micrograms/insect) was applied before or after topical application of KK-42 (10 micrograms/insect) on newly emerged adult females. KK-42 applied alone increased significantly the pre-oviposition period compared to controls. It also significantly delayed egg-laying compared to combined treatments using KK-42 before or after RH-0345. KK-42 applied alone or with and before RH-0345, was found to reduce significantly the duration of oviposition period. Moreover, there was a significant difference in the duration of oviposition period between the two combined treatments. The fecundity was significantly reduced in all treated series compared to controls. In addition, the fecundity recorded in treated series by RH-0345 alone or before KK-42 was significantly higher than in KK-42 treated series. Lastly, the viability of eggs laid was significantly reduced in all treated series compared to controls. Moreover, the combined treatment pronounced the reduction in egg viability. Free ecdysteroids (ecdysone and 20-hydroxyecdysone) in eggs of control and RH-0345 treated females were analyzed by an enzymo-immunoassay using two specific antibodies.

Effects of ingested diflubenzuron on ovarian development during the sexual maturation of mealworms.

Diflubenzuron is the common name of the most potent insecticide belonging to benzoylphenyl urea group. This study describes the effects of orally administered diflubenzuron on ovarian development and structure in mealworms (Tenebrio molitor). Diflubenzuron was found to disturb growth and development of oocytes. It caused a decrease in both the number of oocytes per paired ovaries, the thickness of the follicular epithelium and the length of the basal follicles during the sexual maturation. However, it had no significant effect on the fine structure of follicular cells and basal oocytes examined in vitellogenic phase. These findings suggest that the reduction in fecundity, observed in several insect species by numerous others, is probably due to interference of diflubenzuron with the vitellogenesis via biochemical processes.