Azadirachtin impact on mate choice, female sexual receptivity and male activity in Drosophila melanogaster (Diptera: Drosophilidae)

Azadirachtin, a neem compound (Azadirachta indica) with medical and anti-insect properties, is one the most successful botanical pesticides in agricultural use. However, its controversial impact on non-targeted species and its mechanism of action need to be clarified. In addition, Azadirachtin impact on pre- and post-mating traits remains largely undocumented. The current study examined the effects of Azadirachtin on Drosophila melanogaster as a non-target and model species. Azadirachtin was applied topically at its LD₅₀ (0.63μg) on the day of adult emergence and its effect was evaluated on several traits of reproductive behavior: mate choice, male activity, female sexual receptivity, sperm storage and female sterility. In choice and no choice conditions, only male treatment reduced mating probability. Female treatment impaired mating probability only when males had the choice. Males' mating ability may have been impaired by an effect of the treatment on their mobility. Such an effect was observed in the actimeter, which revealed that treated males were less active than untreated ones, and this effect persisted over 8days. Azadirachtin treatment had, however, no effect on the nycthemeral rhythm of those males. Even when mating occurred, Azadirachtin treatment impaired post-mating responses especially when females or both sexes were treated: remating probability increases and female fertility (presence of larvae) decreases. No impairment was observed on the efficiency of mating, evaluated by the presence of sperm in the spermatheca or the ventral receptacle. Male treatment only had no significant effect on these post-mating responses. These findings provide clear evidence that Azadirachtin alters the reproductive behavior of both sexes in D. melanogaster via mating and post-mating processes.

Effect of an oxadiazine, indoxacarb, on the biochemical composition of ovaries in the German cockroach

Conventional insecticides have been widely used to control cockroaches but these insects have developed resistance to several compounds. Safer insecticides with a low toxicity such as oxadiazine have been advanced: indoxacarb (30% WG) is designated to be a reduced-risk insecticide and is considered as an organophosphate replacement. Insecticidal activity occurs via blockage of the sodium channels in the insect nervous system. In a first series of experiments, the toxicity of different concentrations (15, 20, 25 and 30 ppm) administrated by topical application to newly emerged adults was studied on the German cockroach Blattella germanica, and the LC50 and LT50 values were determined. In a second series of experiments, the compound was applied at its LC50 and LC90 over a period of 6 days, and the effects on the biochemical composition of ovaries (proteins, carbohydrates and lipids) during the adult life (2, 4 and 6 days) were examined.

Effects of tebufenozide on ovarian growth and sexual behavior in the German cockroach (Blattella germanica)

Tebufenozide, a dibenzoylhydrazine insect growth regulator, was applied topically (1 microg/insect) on female adults of the German cockroach Blattella germanica and its effects on ovarian measurement and proteins contents were investigated during the first gonadotrophic cycle (0, 2, 4 and 6 days). Dissection of treated females showed a clear reduction in oocyte numbers and volume of the basal oocyte. The ovarian proteins content was also significantly reduced. Behavioral tests demonstrated that treatment of 6-days-old females with tebufenozide caused in 80% of the males an increase in numbers of antennal contacts, but there was no effect on the numbers of wing raisings. In contrast, it was striking that in 20% of the males there was a total loss of antennal contacts and wings raisings in response to a calling treated female. These behavior effects are probably caused by a reduced production of contact sex pheromone in the females and may help in explaining the lower ovary reproductive parameters.

Cuticular hydrocarbon profiles in Blattella germanica: effects of halofenozide, boric acid and benfuracarb

In order to complete previous studies conducted on Blattella germanica, three insecticides from different groups were evaluated: boric acid, an inorganic compound, benfuracarb, a carbamate, and halofenozide, a non-steroidal ecdysone agonist. Boric acid (8.20%, LD50) and benfuracarb (2%, LD50) were incorporated into the diet and orally administrated to newly emerged adults of both sexes, while halofenozide (0.33%, LD50) was applied topically. Hydrocarbons extracts was made on bidistilled pentane from control and treated series sampled 6 days following treatment. Extracts was analyzed by gas chromatography. Data showed that cuticular profiles of control and treated series were qualitatively similar with thirteen major compounds; however, significant quantitative differences were noted. Boric acid seemed to feminize the cuticular profile in males with a significant reduction of the two first cuticular compounds detected. Halofenozide and benfuracarb reduced cuticular compounds in both sexes.

Effects of a neonicotinoid insecticide (acetamiprid) on acetylcholinesterase activity and cuticular hydrocarbons profil in German cockroaches

Acetamiprid was incorporated into the diet at 2% dose corresponding to the LD50 and orally administrated to newly emerged adults of the German cockroach Blattella germanica and investigated on acetylcholinesterase activity and cuticular hydrocarbons profil. Acetylcholinesterase specific activity was determined on adult males and females after 24, 48 and 72 hours of treatment. Pentanic extracts of cuticular hydrocarbons in males and females after 6 days of treatment were analysed by gas chromatography. Data revealed an increase in acetylcholinesterase activity in both sexes from the control series. However, a significant inhibition in AChE was observed after treatment at 24, 48 and 72 hours especially in females. In addition, hydrocarbons profils were found qualitatively similar in all groups of insects. However, slight quantitative differences between sexes in control series were noted. Acetamiprid feminize the cuticular profil in males with significant reduction of cuticular compound, and these allowed separation of insects into two groups using multivariate analysis.

Reproductive effects in German cockroaches by ecdysteroid agonist RH-0345, juvenile hormone analogue methoprene and carbamate benfuracarb

Blatta germanica is the more prevalent cockroach species in Algeria. In the present study, we tested the effect on reproduction in B. germanica of two insect growth regulators, RH-0345, a benzoylhydrazine analogue that mimics the action of 20-hydroxyecdysone, and methoprene, one of the most commercially important juvenile hormone analogues, and a novel carbamate insecticide, benfuracarb. The compounds were applied topically (10 and 20 microg/insect for RH-0345, and 1 and 10 microg/insect for methoprene) or orally administrated (at 2% for benfuracarb) on newly emerged females and evaluated on reproductive events during the adult life (2, 4 and 6 days). Treatment with RH-0345 and benfuracarb reduced significantly the number of oocytes, the size and the volume of the basal oocyte during the experimental period. Methoprene distorted the ovarian development since it caused a significant reduction in the number of oocytes at 2, 4 and 6 days for the two tested doses, and an increase in oocyte size at 2, 4 and 6 days with 1 microg and a decrease with 10 microg. In a second series of experiments, the effects of these compounds were assayed on the ovarian proteins. Data from biochemical analysis revealed that RH-0345 and benfuracarb reduced the ovarian amounts of proteins, while treatment with methoprene increased it during the sexual maturation.

Comparative action of RH-0345 and pyriproxyfen on molting hormone production and protein analysis in mealworm pupae

RH-0345 (halofenozide) was found to mimic the action of 20-hydroxyecdysone while pyriproxyfen was presented as a juvenile hormone analogue. In this study, RH-0345 (5, 10 micrograms/pupa) and pyriproxyfen (0.10 and 0.20 microgram/pupa), applied topically on newly ecdysed pupae of Tenebrio molitor, were investigated on ecdysteroid titers and hemolymph protein concentrations. During normal pupal development, the ecdysteroid titer measured using an enzyme immunoassay showed a single peak at day 3. The two compounds did not shifted the moment of the pupal ecdysteroid peak. However, RH-0345 at the highest dose (10 micrograms/pupa) increased the ecdysteroid titres recorded from the second day after topical application while pyriproxyfen decreased this hormonal production. In a second series of experiments, the compounds were evaluated on the protein concentrations in the hemolymph. In control pupae, change in protein concentrations showed two peaks. At a 5 micrograms dose, RH-0345 was found to reduce significantly the value of the first peak and at the highest dose, the first peak was not observed and the values recorded following treatment were significantly lower than in controls. Changes in protein concentrations showed that pyriproxyfen suppressed the second peak and the values recorded were either significantly increased at day 2 and 3, either reduced from day 4.

Toxicity of boric acid to Blattella germanica (Dictyoptera: Blattellidae) and analysis of residues in several organs

Pestiferous cockroach species are associated closely with humans and are important from medical and public health points of view. Conventional insecticides have been used widely to control cockroaches which have developed resistance to these compounds. Thus, interest has again centered on lesser-used compounds such as boric acid. Boric acid has been used as an insecticide for many years, especially against cockroach. Its mode of action on insects has not been satisfactorily established. In Algeria, Blattella germanica (Dictyoptera: Blattellidae) is a serious pest in the urban environment and their infestation were controlled for many years by organophosphate, carbamate or pyrethroid insecticides. In order to obtain more information on the mode of action of boric acid, we first evaluated the oral toxicity of boric acid on B. germanica adults. Then, the compound was determined in several organs by an colorimetric method. This insecticide was incorporated into the diet and orally administered at different concentrations ranging from 1 to 40% (w/w) to newly emerged adults. Mortality was recorded at different times during treatment (24, 48, 72 and 144 h). Treatment resulted in a dose-dependent mortality since the LD50 (%) recorded are 85 at 24 h, 67 at 48 h, 39 at 72 h and 8 at 144 h, respectively. Then the quantity of boric acid accumulated in several organs (hemolymph, gut, ovaries, testicles and fat body) was determined as function the duration of treatment (1 to 5 days) for two doses (LD50 and LD90). Results revealed that bioaccumulation of residues in these organs increased as function the duration of treatment. In addition, relatively important amounts of residues, are detected in fat body.

Ecdysteroid titres in a tenebrionid beetle, Zophobas atratus: effects of grouping and isolation

Metamorphosis in Zophobas atratus is dependent on isolation: when kept in grouped conditions, larvae undergo numerous supernumerary moults, growing in size, without pupating. This beetle thus represents an interesting model for the analysis of possible differences in the endocrine regulation of normal vs. supernumerary larval moults. In this study, the ecdysteroid titres have been analysed in this species, using enzyme immunoassay. The hormonal variations of larvae undergoing normal or supernumerary larval cycles were particularly examined, in either grouped or isolated conditions. Normal larval cycles presented very similar ecdysteroid variations in grouped as well as isolated conditions, showing a single hormonal peak (at about 1000pg/&mgr;l). Supplementary larval cycles, occurring in grouped conditions, also showed a similar single ecdysteroid peak, but after a longer period of basal levels. Isolation of such larvae triggered their larval-pupal transformation, which was characterized by more complex hormonal fluctuations, including a small ecdysteroid peak before the main one. Interestingly, the isolation of big larvae during a large part of their cycle induced this peculiar hormonal pattern synchronously, confirming the involvement of a complex neuroendocrine control between external conditions and ecdysteroid titres.

2-Deoxyecdysone is a circulating ecdysteroid in the beetle Zophobas atratus

A qualitative analysis of ecdysteroids has been performed during the post-embryonic development of the tenebrionid beetle, Zophobas atratus, by high performance liquid chromatography (HPLC) combined with enzyme immunoassay (EIA) using two different antibodies. Three HPLC peaks were found to be immunoreactive, in hemolymph extracts of both sexes. Moreover, these peaks had ecdysteroid-like UV spectra, determined using a photodiode array detector. The use of two different HPLC systems (reverse and normal phases), in combination with two different EIA antibodies, allowed us to identify 20-hydroxyecdysone (20E) and ecdysone (E), as the two main ecdysteroids, but also suggested the presence of 2-deoxyecdysone (2dE) as the third hemolymph component. Secretion of putative 2dE, together with E (but not 20E) was also demonstrated in vitro from incubations of prothoracic glands and of tegumental explants. In these experiments, either in vivo or in vitro, 3-dehydroecdysone was never observed. Our observations thus strongly suggest that 2dE is a circulating ecdysteroid in Z. atratus and may function as a prohormone during the development of some insects.