[Azadirachtin, a natural pesticide with multiple effects]. / L'azadirachtine, un pesticide naturel aux effets multiples.

There are many studies devoted to the negative impact of conventional pesticides that effectively control pests, but cause widespread environmental pollution. As a result, interest is growing in pesticides of a natural origin with a lower environmental impact. Among them, azadirachtin, sold under various formulations (neem oil, Neem-Azal, Bioneem, etc.), is still the most widely recommended molecule in agricultural ecosystems. Azadirachtin has also been used in traditional medicine for centuries, and studies published over the past few years have tended to support its therapeutic use. Yet the argument that azadirachtin is harmless to the environment has been offset by its notable collateral and controversial effects on non-target organisms. The present paper summarizes the work already done in this field.

TITLE: L'azadirachtine, un pesticide naturel aux effets multiples. ABSTRACT: Une littérature abondante traite de l'impact négatif des pesticides conventionnels, très efficaces dans la gestion des ravageurs mais responsables d'une large pollution environnementale. Les pesticides d'origine naturelle qui auraient un moindre impact environnemental suscitent ainsi un intérêt majeur. Parmi ceux-ci, l'azadirachtine, commercialisée sous diverses formulations (huile de neem, Neem-Azal, Bioneem, etc.) reste la molécule la plus recommandée dans les agro-écosystèmes. L'argument d'une innocuité environnementale de l'azadirachtine est cependant nuancé par des effets collatéraux qui, bien que controversés, sont notables sur des organismes non ciblés.

Azadirachtin effects on mating success, gametic abnormalities and progeny survival in Drosophila melanogaster (Diptera).

BACKGROUND: Azadirachtin is a prominent natural pesticide and represents an alternative to conventional insecticides. It has been successfully used against insect pests. However, its effects on reproduction require further analysis. Here we investigated lethal and sublethal effects of azadirachtin, on treated adults in a model insect, Drosophila melanogaster (Meigen). Dose-mortality relationships as well as several parameters of reproduction (mating, spermatogenesis, oogenesis and fertility) were examined. RESULTS: Neem-Azal, a commercial formulation of azadirachtin, applied topically on newly emerged adults, increased mortality with a positive dose-dependent relationship. The LD50 (0.63 µg) was determined 24 h after treatment using a non-linear regression. Adults surviving this dose had a mating success that was divided by 3 and a progeny production reduced by half when males were treated, and even more when females were treated. When combining probability of survival, of mating and reduced progeny, it appeared that LD50 induced a 98% reduction in reproductive rates. Reduced progeny was partially explained by the effect of adult treatment on gametes number and abnormalities. The number of cysts and the apical nuclei positions within the cysts decreased by 29.7% and 20%, respectively, in males. In females, the number of oocytes per ovary and the volume of basal oocytes also decreased by 16.1% and 32.4%, respectively. CONCLUSION: Azadirachtin causes significant toxic effects in both sexes and decreases the fecundity and fertility of D. melanogaster. Females are more sensitive to azadirachtin. © 2017 Society of Chemical Industry.

Azadirachtin induced larval avoidance and antifeeding by disruption of food intake and digestive enzymes in Drosophila melanogaster (Diptera: Drosophilidae).

Botanical insecticides are a promising alternative to reduce the harmful effects of synthetic chemicals. Among the botanical biopesticides, azadirachtin obtained from the Indian neem tree Azadirachta indica A. Juss. (Meliaceae) is probably the biorational insecticide with greatest agriculture use nowadays due to its broad insecticide activity. The current study, evaluated the lethal and sublethal effects of azadirachtin on larval avoidance, food intake and digestive enzymes of Drosophila melanogaster larvae as biological model. Azadirachtin was applied topically at two doses LD25 (0.28µg) and LD50 (0.67µg) on early third instars larvae. Results evaluated 24h after treatment showed that larvae exhibited significant repellence to azadirachtin and prefer keeping in untreated arenas rather than moving to treated one. In addition, azadirachtin avoidance was more marked in larvae previously treated with this compound as compared with naïf larvae (controls). Moreover, azadirachtin treatment decreased significantly the amount of larval food intake. Finally, azadirachtin reduced significantly the activity of larval α-amylase, chitinase and protease and increased the activity of lipase. This finding showed that azadirachtin induced behavioral and physiological disruption affecting the ability of the insect to digest food. This rapid installation of avoidance and long term antifeedancy might reinforce the action of azadirachtin and provide a new behavioral strategy for integrated pest management programs.

Preimaginal exposure to azadirachtin affects food selection and digestive enzymes in adults of Drosophila melanogaster (Diptera: Drosophilidae).

Among the plant derived product, azadirachtin, a neem-based insecticide, is exceptional in having a broad range of bioactivity including toxicity, growth, development and reproduction effects, repellency and antifeedancy. If considerable progress on the physiological and biological activities and agricultural application of azadirachtin has been achieved, its exact mechanism of action remains uncertain. In this study, we aimed at assessing the lethal and sublethal behavioral and physiological effects of azadirachtin on Drosophila melanogaster Meigen, 1830 (Diptera: Drosophilidae) as biological model. Azadirachtin was applied topically at two doses LD25 (0.28µg) and LD50 (0.67µg) on early third instar larvae. Results showed that flies preferentially ingested control medium rather than azadirachtin-treated medium. Pre-imaginal exposure (L3) to azadirachtin increased aversion to this substance suggesting a memorability of the learned avoidance. In addition, all tested flies revealed a clear preference for solvent odour rather than azadirachtin odour. Moreover, azadirachtin treatment decreased significantly the amount of food intake in the adults of both sexes. Finally, azadirachtin was found to affect digestive enzyme activities in the midgut of flies. Indeed, an inhibition of α-amylase, chitinase, and protease activities and an increase of lipasic activity were noted. These results may reflect interference of azadirachtin with regulation of feeding and metabolism, and provide some evidence of a long term antifeedancy and delayed effects through developmental stage which may reinforce the insecticidal activity of this bioinsecticide.

Larval exposure to azadirachtin affects fitness and oviposition site preference of Drosophila melanogaster.

Azadirachtin, a biorational insecticide, is one of the prominent biopesticide commercialized today and represent an alternative to conventional insecticides. The current study examined the lethal and sublethal effects of azadirachtin on Drosophila melanogaster Meigen, 1830 (Diptera: Drosophilidae) as biological model. Various doses ranging from 0.1 to 2µg were applied topically on early third instar larvae and the cumulative mortality of immature stage was determined. In second series of experiments, azadirachtin was applied at its LD25 (0.28µg) and LD50 (0.67µg) and evaluated on fitness (development duration, fecundity, adult survival) and oviposition site preference with and without choice. Results showed that azadirachtin increased significantly at the two tested doses the duration of larval and pupal development. Moreover, azadirachtin treatment reduced significantly adult's survival of both sex as compared to control. In addition, azadirachtin affected fecundity of flies by a significant reduction of the number of eggs laid. Finally results showed that females present clear preference for oviposition in control medium. Pre-imaginal exposure (L3) to azadirachtin increased aversion to this substance suggesting a memorability of the learned avoidance. The results provide some evidence that larval exposure to azadirachtin altered adult oviposition preference as well as major fitness traits of D. melanogaster. Theses finding may reinforce behavioural avoidance of azadirachtin and contribute as repellent strategies in integrated pest management programmes.

Biochemical and histological effects of gibberellic acid on Locusta migratoria migratoria fifth instar larvae.

Experiments were conducted to assess the effect of gibberellic acid (GA3), a plant growth regulator, on Locusta migratoria migratoria fifth instar larvae. Newly emerged larvae were exposed to various concentrations of GA3 administered by topical application or by forced ingestion. Results showed that treated insects exhibited toxic symptoms with a dose-dependent mortality. GA3 toxicity was also demonstrated by perturbation of the moult processes. In fact, we noted that treated insects present exuviations difficulties due to the impossibility to reject the old integuments causing mortality in the 5th instar larvae. Histological study of proventriculus revealed alterations in the epithelial cells and absence of apolysis phenomenon. Data also showed that GA3 induced significant quantitative variation of haemolymph metabolites. These changes result in a significant decrease in the total concentration of proteins and carbohydrates and an increase in the total concentration of haemolymph lipids.