Nadia Aribi

Insecticidal Activity of Azadirachtin on Drosophila melanogaster and Recovery of Normal Status by Exogenous 20-Hydroxyecdysone

Azadirachtin, an insect growth disruptor, is known to be an antagonist of the juvenile hormone and 20-hydroxyecdysone (20E). However, its mechanism of action remains to be understood. Furthermore, the effects of the interaction of azadirachtin and 20E have not been investigated. The current study examined the effect of azadirachtin topically applied alone or in combination with 20E on Drosophila melanogaster Meigen, 1830 (Diptera: Drosophilidae). In initial bioassays, various doses (0.5, 1, 1.5, 2.5 and 4.5 µg) of azadirachtin was tested alone on newly ecdysed pupae and the inhibition doses (ID) of adult emergence determined. In a follow-up experiment, azadirachtin applied alone at its ID25 (0.59 µg) and ID50 (1.10 µg) was evaluated on catalase (CAT) and glutathion S-transferase (GST) activities, and yolk protein content in fat body and ovaries. Results showed that azadirachtin at the two tested doses increased significantly the activity of both GST at 48 and 72 hours, and CAT at 24, 48 and 72 hours following treatment. Moreover, azadirachtin treatment at these doses reduced significantly the yolk protein content in fat body and ovaries as compared to the control series. Finally, the exogenous 20E (0.25 and 0.50 µg), applied 24 or 48 h after azadirachtin treatment, relatively restored the normal values of CAT, GST and yolk protein content in fat body and ovaries. All these results indicate that exogenous 20E can compensate the depressive effects induced by azadirachtin on D. melanogaster.

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 adults 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.

Comparative effectiveness of some acaricides used to control Varroa destructor (Mesostigmata: Varroidae) in Algeria

In this study the effectiveness of two synthetic (Bayvarol and Apivar) and two natural acaricides (Apiguard and ApiLife Var) against Varroa destructor were evaluated with use of infested colonies of Apis mellifera intermissa, housed in Langstroth standard hives. Each acaricide was tested in five hives, and one group of five hives was left untreated as the control. All acaricides significantly reduced the levels of varroa mite infestation on adult honeybees and worker brood, but the efficacy was higher for Apiguard (93–97 %) and ApiLife Var (94–98 %) compared to Bayvarol (85–90 %) and Apivar (82–88 %). Overall, the data indicated that essential oils like Apiguard and ApiLife Var can be recommended in the control of V. destructor, while synthetic varroacides like Bayvarol and Apivar should be minimized due to increased mite resistance for these products.

Laboratory evaluation of azadirachtin against the oriental cockroach, Blatta orientalis L. (Dictyoptera, Blattellidae): Insecticidal activity and reproductive effects

In this work, the toxicity of azadirachtin applied topically at various doses (300, 600, 1200, 2400, 4800 and 9000 ng/ insect) was evaluated against newly emerged adults of the oriental cockroach, Blatta orientalis L. (Dictyoptera, Blattellidae) under laboratory conditions. Results show that treated insects exhibited toxic symptoms with a dose-dependent mortality. In a second series of experiments, the compound applied topically at its LD 50 and LD 90 on newly emerged female adults was investigated on ovarian growth during the first gonadotrophic cycle (0, 2, 4 and 6 days). Azadirachtin was found to reduce the number of oocytes per paired ovaries and the size of basal oocytes. Furthermore, the compound was examined on ovarian biochemical components. Biochemical data revealed a significant reduction of ovarian contents of proteins, lipids and carbohydrates with the two tested doses. The overall results suggest an interference of the compounds with the vitellogenesis.

A scientific note on the impact of acaracides on the nutritional biochemistry of Apis mellifera intermissa (Hymenoptera: Apidae)

is a serious parasiticmite of honeybees worldwide. In general, the con-trol of this mite is obtained by the use of severalacaricides. Little has been reported on the side-effects of these treatments on honeybees (Haarmannet al., 2002; Gregorc et al., 2007) and there hasbeen no research on the biochemical effects on thehost after exposure to acaracides. Likewise, morestudies on these acaricides are needed to evalu-ate their possible negative effects on the honey-bee populations. The aim of this work was todetermine secondary effects of four acaricides treat-ments on the metabolism of the bees by measuringthe amounts of protein, carbohydrates and lipids inthe hemolymph and body tissues of newly emergedworker bees, nurses and forager bees. The fouracaracides tested were two synthetic compoundsBayvarol and Apivar and two naturally derivedtreatments, Apiguard and ApiLife Var.The experiments were carried out in an apiary ofhoneybees derived from

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.

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.

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.

Effects of gibberellic acid on ovarian biochemical composition and ecdysteroid amounts in the migratory locust Locusta migratoria (Orthoptera, Acrididae)

Migratory locusts represent the most important crop pests in Africa and Asia. Because environmental damages are associated with the use of synthetic insecticides in locust and grasshopper control, new environmentally acceptable approaches are becoming increasingly important. The effects of gibberellic acid (GA3), a plant growth regulator, was investigated by topical application and ingestion on the reproductive physiology and ecdysteroids production of the migratory locust Locusta migratoria at concentrations of 125, 625, 3125, 4125, 5125 and 6125 μg/mL. The treatment applied to adult females during the pre-ovipositional phase provokes a significant adverse influence on their reproductive potential. Indeed, GA3 significantly reduced both fecundity and fertility. Gibberellic acid also caused disturbances in the incorporation of the hemolymph metabolites (proteins, carbohydrates and lipids) in the oocyte resulting in a significant reduction in their concentrations in the ovaries. Ecdysteroid production was measured by an enzymo-immunoassay. GA3, administered by ingestion to the adult females, significantly reduced the ecdysteroid titers in ovaries and freshly laid eggs.

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.