Phytochemical composition of almond oil from Melia azedarach L. and its larvicidal, ovicidal, repellent and enzyme activities in Culex pipiens L

Melia azedarach L. (Meliaceae) is a botanical species with focal point of global research for its biological properties. The Melia azedarach tree is distinguished by its rapid growth, its adaptation to different temperate zones, as well as its insecticidal properties. All this made us think of exploiting it in biological control against different stages of mosquitoes. To this end, we aim, through the present work, to evaluate the effectiveness of Melia azedarach extracts against Culex pipiens mosquito. More specifically, our study focuses on determining the chemical composition of Melia almond oil, as well as the larvicidal, ovicidal and repellent activities on Culex pipiens L. mosquito as well as the activities of acetylcholinesterase (AChE) and glutathione-S-transferase (GST). Almond oil was extracted by a Soxhlet and subjected to gas chromatography-mass spectrometry (GC/MS). The yield was found to be 35.17%. The chemical composition revealed the presence of various phytoconstituents. A total of 7 compounds were identified, the main ones being 9,11-Octadecadienoic acid, methyl ester, (E,E)- (79.32%), 9-octadecenoic acid (Z)-, methyl ester (13.24%), hexadecanoic acid and methyl ester (3.69%). The larvicidal bioassays were performed according to the protocol recommended by the World Health Organization with concentrations varying from 20 to 80 mg/L depending on the exposure time (24, 48 and 72 hours). The almond oil exhibited remarkable larvicidal activity against fourth instar larvae and the lethal concentrations were determined (LC₂₅= 23.70 mg/L, LC₅₀=35.49 mg/L, LC₉₀=79.61 mg/L). The results also showed that the oil caused an ovicidal activity with a significant effect on egg hatch. The recorded hatching percentages were respectively 88.79% and 72.40% for the LC₂₅ and LC₅₀, and this compared to the control series. Moreover, this oil exhibited significant repellency against adult mosquitoes. Furthermore, the enzymatic measurements performed on LC₅₀ and LC₉₀ treated larvae revealed a neurotoxic activity and a stimulation of the detoxification system as evidenced, respectively, by an inhibition of AChE and induction in GST activity. Overall, our data proved that Melia azedarach almond oil could be considered as a potent biorational alternative to synthetic insecticides for mosquito control.

Multibiomarker responses after exposure to a sublethal concentration of thiamethoxam in the African honeybee (Apis mellifera intermissa)

Thiamethoxam is an insecticide mainly used in agriculture to control insect pests. However, non-target insect species, such as honeybees, may also be impacted. In this study, adults of Apis mellifera intermissa were orally exposed under laboratory conditions to a sublethal concentration of thiamethoxam (CL₂₅₌ 0.17 ng/μl) for 9 days and the effects were evaluated at the biochemical level, by monitoring specific oxidative stress and neuronal biomarkers. Results showed an increase in the antioxidant enzymes, glutatione-S-transferase (GST), catalase (CAT) and glutathione peroxidase (GPx) and in content of malondialdehyde (MDA). The activity of acetylcholinesterase (AChE) was downregulated as evidence of a neurotoxic action and no significant change was observed in glutathione (GSH). Exposure to the insecticide thiamethoxam induced oxidative stress and defense mechanisms affecting honeybee physiology.

Pre-imaginal exposure to Oberon® disrupts fatty acid composition, cuticular hydrocarbon profile and sexual behavior in Drosophila melanogaster adults

Oberon® is a commercial formulation of spiromesifen, a pesticide inhibitor of lipid biosynthesis via acetyl CoA carboxylase, widely used in agricultural crop protection. However, its mode of action requires further analysis. We currently examined the effect of this product on Drosophila melanogaster as a non-target and model organism. Different concentrations of spiromesifen were administered by ingestion (and contact) during pre-imaginal development, and we evaluated its delayed action on adults. Our results suggest that spiromesifen induced insecticidal activity on D. melanogaster. Moreover, spiromesifen treatment significantly increased the duration of larval and pupal development at all tested concentrations while it shortened longevity in exposed males as compared to control males. Also, pre-imaginal exposure to spiromesifen quantitatively affected fatty acids supporting its primary mode of action on lipid synthesis. In addition, this product was found to modify cuticular hydrocarbon profiles in exposed female and male flies as well as their sexual behavior and reproductive capacity.

Evaluation of the pesticide Oberon on a model organism Drosophila melanogaster via topical toxicity test on biochemical and reproductive parameters

Spiromesifen (Oberon® 240 SC), a pesticide widely used to control pests like mites and whiteflies, was investigated using Drosophila melanogaster Meigen, 1830 (Diptera, Drosophilidae) as a model organism. The compound was applied topically at two concentrations (LC₁₀: 21.45 and LC₂₅: 39.53 μg active ingredient/pupa), on newly molted pupae and assessed on morphometric measurements of ovaries and the progeny of surviving adults. Results showed that spiromesifen inhibited the growth and development of ovaries, reducing at the highest dose (LC₂₅) the number of oocytes, the volume of basal oocytes and ovarian weight. Biochemical analysis revealed that the tested compound reduced the ovarian levels of carbohydrates and glycogen during the sexual maturation. Moreover, fecundity, fertility and number of descendants from parents that survived to the treatment of pupae were significantly reduced. The sex ratio determined indicated a significant decrease in treated series and males seemed more sensitive to spiromesifen than females. Lastly, the compound was found to affect the sexual behavior.

Nephroprotective effect of estrogen and progesterone combination on cisplatin-induced nephrotoxicity in ovariectomized female rats

Recently, we reported that estrogen (Es) has no beneficial effect on cisplatin (CP)-induced nephrotoxicity, but the role of progesterone (Pr) and the combination of Es and Pr are not yet well-defined. In this study, we investigated the protective role of Pr, and co-administration of Es/Pr on CP-induced nephrotoxicity. Eighty-six ovariectomized female Wistar rats were divided into 13 groups, and the experiments were performed in two phases. In Phase I, Groups 1-4 received 2, 5, 10, and 25 mg/kg, IM Pr dissolved in sesame oil every 5 days for four doses. Groups 5-8 had the same treatment regimen as Groups 1-4, but after the third injection the animals also received continuous dose of CP (2.5 mg/kg/day, i.p.) for 8 days. Group 9, as the positive control group, received sesame oil instead of Pr plus CP. Group 10, as the negative control group, received sesame oil instead of Pr. After the most effective dose of Pr was determined in Phase I, Groups 11-13 in Phase II received 10 mg/kg Pr plus either 0.25, 0.5, or 1 mg/kg, IM estradiol valerate every 5 days for four doses. After the third injection, they also received a continuous dose of CP for 8 days. The levels of blood urea nitrogen (BUN) and creatinine (Cr), kidney tissue damage score (KTDS), and kidney weight (KW) increased and body weight (BW) decreased in the positive control group (P < 0.05). Administration of Pr (10 mg/kg) plus CP decreased KTDS and BW loss and KW. Co-administration of ES/Pr at specific doses improved Cr, BUN, and KTDS; and resulted in reduced CP-induced nephrotoxicity. The results obtained suggest that the beneficial effect of Pr on CP-induced nephrotoxicity is dose-dependent. In addition, combination of Es/Pr with a specific dose decreased CP-induced nephrotoxicity.

Assessment of experimental thermal, numerical, and mandibular drilling factors in implantology

The main factors that cause an increase in the temperature of the jaw during drilling when implanting teeth are the geometric measurements of the surgical drill, its rotational speed, and its feed rate (cutting speed). Using finite element modelling we analysed the effect of the three variables - the angle of the head of the drill bit, the rotational speed, and the feed rate - on the increase in the temperature of the bone at the point of the drill. This showed that drilling with the angle of the head of the drill bit at 70° generates a lower temperature than when it is at 90° or 118°. The same is true when the drill bit is set at 200 rotations/minute (rpm) compared with 400,800, or 1200rpm. When the feed rate of the drill bit is 120mm/minute it generates less heat than when it is at 90 or 60mm/minute. An increase in temperature during drilling of the jaw has a direct relation with the rotational speed of the drill bit, and a reverse relation to its feed rate. The sharper the drill bit, the lower the temperature during drilling.

Pyrimidine-2-thione derivatives as corrosion inhibitors for mild steel in acidic environments

Quantum chemical calculations show that the area containing a S atom is a possible site for bonding with the mild steel surface.

Use of the land snail Helix aspersa for monitoring heavy metal soil contamination in Northeast Algeria

The objective of this study was to investigate the impact of anthropogenic activities on soil quality using the land snail Helix aspersa as a bioindicator. Soil samples and snails were collected from several sites in Northeast Algeria during the summer and winter of 2010. All of the sites were chosen due to their proximity to industrial factories-a potential source of soil pollution via heavy metal contamination. The concentration of heavy metals (Pb, Cd, Mn, and Fe) in soil samples was analyzed using atomic absorption spectrophotometry. Activity levels of glutathione S-transferase (GST) and acetylcholinesterase (AChE), indicators of oxidative stress and neurotoxicity, respectively, were measured in snails collected from each site. GST and AChE activity were found to vary between sites and by season. The highest levels of GST activity were registered during the summer at sites closest to potential sources of pollution. AChE activity levels also peaked during the summer with the highest values recorded at the site in El Hadjar. These increased levels of bioindicative stress response correlated with increasing metal concentration in soil samples collected at each site.

The simultaneous efect of extrusion and T6 treatment on the mechanical properties of Al-15wt.%Mg2Si composite

This article investigates the simultaneous efect of extrusion ratio and T6 heat treatment on microstructure and mechanical properties of in-situ Al-15wt.%Mg2Si composite. his composite has already been introduced as a new class of light materials but the brittle structure of the primary Mg2Si which is formed during solidiication limits its application. As-cast composite was directly extruded as rod by using three diferent dies. Ater T6 heat treatment on extruded samples, microstructure was studied by optical and scanning electron microscopy. Results demonstrated that extruded and heat treated composite possesses considerably higher strength and enhanced ductility in comparison with the as-cast samples. It was also found that heat treatment and extrusion processes change the primary Mg2Si morphology considerably and its size increases as extrusion ratio decreased. Fracture surface examinations revealed a transition from brittle fracture mode in as-cast composite to ductile fracture in heat treated and extruded specimens. his can be attributed to the changes in size and morphology of Mg2Si intermetallics and porosity content.

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.

Impact of the insect growth regulator diflubenzuron on biochemical composition of cuticle of the shrimp Penaeus kerathurus

Diflubenzuron (Dimilin 25WP) is an insecticide of the class of benzoylphenylurea (BPUs) and is widely used in the control of insect pest in agriculture and forestry. Typically, these chemistries prevent the moulting process by inhibiting chitin formation and thereby causing abnormal cuticular deposition and abortive moulting in insect and crustacean species. In a previous study, we have shown that diflubenzuron could cause a modification in the lamellar ultrastructural, particularly in the membranous layers, in the non-target organism, the caramote prawn or triple-grooved shrimp Penaeus kerathurus (Forskal, 1775) (Decapoda, Peneidae). Therefore, the aim of this study was to evaluate under laboratory conditions the potential side-effects of diflubenzuron on the biochemical composition of the cuticle of treated P. kerathurus. Diflubenzuron was added to the rearing seawater at a final concentration of 1 microg/L) and newly-ecdysed adult shrimps were exposed for 10 days, i.e. until stage C during the molting cycle. The most typical treatment symptoms were a significantly reduced thickness of both the principal and membranous layers, and reduced amounts of chitin in the cuticle. These symptoms help in explaining the structural alterations observed in treated cuticles, and confirm the primary mode of action of diflubenzuron to inhibit chitin biosynthesis.

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.

Evaluation of halofenozide against prey mosquito larvae Culex pipiens and the predator fish Gambusia affinis: impact on growth and enzymatic activities

Culex pipiens (Diptera: Culicidae) is the most widely distributed mosquito species in Algeria and many other countries in the world. Mosquitoes are generally controlled by conventional insecticides but these may pose strong secondary effects on the environment. In this context, the insect growth regulators (IGRs) have shown promise in controlling pest insects. Halofenozide (23% EC) is a novel IGRs belonging to the class of non-steroidal ecdysone agonists, and it was found toxic for larvae of C. pipiens. In addition biological methods constitute an alternative to chemical control. Several fish species have been tested against mosquitoes, and Gambusia affinis was found very efficient. In the present study we evaluated the impact of this new potent insecticide (halofenozide) on growth and metric indexes in the larvivorous fish G. affinis under laboratory conditions. In addition, the effects were evaluated on the enzymatic activities of acetyl cholinesterase (AChE) and glutathione S-transferase (GST). The insecticide was added in water at two concentrations (12.6 and 28.6 microg/L) corresponding to the LC50 and LC90 obtained against fourth instar larvae of C. pipiens, and adult females of G. affinis were exposed to halofenozide for 30 days. At different exposure times we measured the length and weight of fishes, the index of condition (K), the gonado-somatic ratio (GSR) and the hepato-somatic ratio (HSR). The results showed that halofenozide had no significant (p>0.05) effects on growth, metric indexes and AChE activities. However, treatment caused a significant induction (p<0.05) in GST activities at days 15 and 30 with the highest dose. Our results indicate that this ecdysteroid agonist presented only minor secondary effects on the non-target fish species, and so it has potential for controlling of mosquitoes in an integrated manner.

Laboratory evaluation of Bacillus thuringiensis (Vectobac WDG) against mosquito larvae, Culex pipiens and Culiseta longiareolata

Mosquitoes are vectors of many human diseases and cause environmental nuisances. Due to their Large geographical distribution and abundance, Culex pipiens and Culiseta longiareolata represent the most important mosquito species in ALgeria and many countries in the world. They are generally controlled by conventional insecticides. The high reproductive ability and development of insecticide resistance of mosquito species are Leading to a search for novel molecules. As so, Vectobac that is based on the insecticidal toxins of Bacillus thuringiensis isroelensis (Bti), may provide economical control of mosquito larvae. In this study, we tested the activity of Vectobac (WDG) at different concentrations, ranging between 2 and 30 microg/L, against the different Larval stages (L1-L4) of Cx. pipiens and C. longiareolata. Bioassays were done on newly moulted Larvae under Laboratory conditions according to the guidelines of WHO. In Cx. pipiens, mortality was scored already after 24 h, and in addition developmental effects were observed like inhibition of growth with incomplete moulting and failure of adult emergence. From a dose-response curve LC50 were calculated: 9.22 microg/L for L1 and 35.33 microg/L for L4. For C. longiareolata, the respective LC50's were 6.05 microg/L and 23 microg/L for L1 and L4. The results are discussed in relation to the susceptibility of the two mosquito species tested, lethaL doses, direct toxicity, and effects on growth and development.

In vivo expression of GLP-1/IgG-Fc fusion protein enhances beta-cell mass and protects against streptozotocin-induced diabetes

Glucagon-like peptide 1 (GLP-1) and its analogue exendin-4 (Ex4) have displayed potent glucose homeostasis-modulating characteristics in type 2 diabetes (T2D). However, there are few reports of effectiveness in type 1 diabetes (T1D) therapy, where there is massive loss of beta cells. We previously described a novel GLP-1 analogue consisting of the fusion of active GLP-1 and IgG heavy chain constant regions (GLP-1/IgG-Fc), and showed that in vivo expression of the protein, via electroporation-enhanced intramuscular plasmid-based gene transfer, normalized blood glucose levels in T2D-prone db/db mice. In the present study, GLP-1/IgG-Fc and Ex4/IgG-Fc were independently tested in multiple low-dose streptozotocin-induced T1D. Both GLP-1/IgG-Fc and Ex4/IgG-Fc effectively reduced fed blood glucose levels in treated mice and ameliorated diabetes symptoms, where as control IgG-Fc had no effect. Treatment with GLP-1/IgG-Fc or Ex4/IgG-Fc improved glucose tolerance and increased circulating insulin and GLP-1 levels. It also significantly enhanced islet beta-cell mass, which is likely a major factor in the amelioration of diabetes. This suggests that GLP-1/IgG-Fc gene therapy may be applicable to diseases where there is either acute or chronic beta-cell injury.

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.

Column preconcentration of gold by adsorbing AuCl4− onto methyltrioctyl ammonium chloride–naphthalene and subsequent atomic absorption spectrometric determination

A sensitive, selective and simple preconcentration method for ultra-trace gold determination has been developed that uses naphthalene-methyltrioctyl ammonium chloride (Aliquat 336s) as an adsorbent. Gold, in the form of AuCl4-, was retained by the adsorbent in the column at a flow rate of 1 ml min(-1). After filtration, the solid mass consisting of the gold complex and naphthalene was dissolved out of the column with 5 ml of N,N-dimethylformamide (DMF), and the metal was then determined by atomic absorption spectrometry. In the initial solution, the calibration graph of absorbance versus gold concentration was found to be linear in the range 0.5-150 ng ml(-1) Au(III) with r=0.997 (n=9), and the 3 s detection limit was 0.428 ng ml(-1). The relative standard deviation for eight replicate measurements of 20 microg of gold was 2.14%. Preconcentration factors of 390 and 650 were achieved using 5 ml and 3 ml of DMF, respectively. The proposed method was successfully applied to the determination of gold in wastewater, processed pool water, slurry pool water, and raw well-water from the Moteh gold mine, and synthetic samples.

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.

Activity of kk-42 in combinated treatment with RH-0345 or 20-hydroxyecdysone on morphometric measurements and free ecdysteroid in eggs of mealworms

RH-0345 (halofenozide), a bisacylhydrazine derivative, is a nonsteroidal ecdysteroid agonist that mimics the action of the moulting hormones, while KK-42, an imidazole compound, is a potent inhibitor of ecdysteroid biosynthesis. Recent experiments with Tenebrio molitor suggested that the reduction of ecdysteroid titer, leading to a reduction of reproductive capacity, is due to a direct and rapid action of KK-42 on ecdysterold biosynthesis. Moreover, RH-0345 could partly restore the effects on reproductive events induced by KK-42. On the other hand, RH-0345 was found to affect growth and development of ovaries in a manner similar to that 20-hydroxyecdysone (20-E) and increased the ecdysteroid production. Therefore, the present study evaluates KK-42 applied topically (10 microg/insect) in combination with RH-0345 or 20-E in order to obtain more information on the mode of action of this compound on reproduction in T. molitor. In a first series of experiments, the compounds were assayed on morphometric measurements of freshly laid eggs. Results showed that both the weight and the volume of eggs increase significantly in series treated by KK-42 followed by 20-hydroxyecdysone as compared to controls and treated series by KK-42 followed by RH-0345. Data from enzyme immunoassay measurements revealed that KK-42 applied before 20-E was found to reduce significantly the amounts of free ecdysteroids in eggs comparatively to the others series.

QSAR analysis for ADA upon interaction with a series of adenine derivatives as inhibitors

The kinetic parameters of adenosine deaminase such as Km and Ki were determined in the absence and presence of adenine derivatives (R1-R24) in sodium phosphate buffer (50 mM; pH 7.5) solution at 27 degrees C. These kinetic parameters were used for QSAR analysis. As such, we found some theoretical descriptors to which the binding affinity of adenosine deaminase (ADA) towards several adenine nucleosides as inhibitors is correlated. QSAR analysis has revealed that binding affinity of the adenine nucleosides upon interaction with ADA depends on the molecular volume, dipole moment of the molecule, electric charge around the N1 atom, and the highest of positive charge for the related molecules.

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.

Insecticidal activity of a nonsteroidal moulting hormone agonist on mosquito larvae and effects on ecdysteroid amounts

The secondary effects of conventional insecticides on the environment, vertebrates and beneficial organisms have caused a move to the use of more target-specific chemicals such as insect growth regulators. Halofenozide (RH-0345) is a novel nonsteroidal ecdysteroid agonist that induces a precocious and incomplete moult in several insect orders. In the present study, the insecticidal activity of a commercial formulation of halofenozide (23% EC) was evaluated at different concentrations ranging between 8 and 32 micrograms/l. Treatment was made on newly moulted fourth-instar larvae of the mosquito, Culex pipiens (Diptera: Culicidae), and mortality was scored until adult emergence. Results showed that death in the larval stage was relatively important. Moreover, treatment caused a significant reduction in the length of the larval and pupal stage. In a second series of experiments, halofenozide was tested at two doses (LC50 = 12.58 micrograms/l and LC90 = 28.58 micrograms/l) and the ecdysteroid amounts during the fourth instar were evaluated in an enzyme immunoassay. We noted that halofenozide did not shifted the moment of the single larval ecdysteroid peak, but it caused an increase of the titre values. Finally, the compound at the highest concentration was found to increase significantly the cuticle thickness recorded at day 4 following treatment.

Effects of diflubenzuron on growth and glutathione in mosquito fish (Gambusia affinis)

Although some biological control agents and related biorational approaches are available for mosquito control, insecticides remain the principal control method. In addition, the secondary affects of conventional insecticides in environment has led to the discovery of more target-specific chemical such as insect growth regulators. Dimilin (25% WP), the common name of diflubenzuron, prevent molting by interfering with chitin synthesis in several insect orders. This study evaluate toxicity of this insecticide on a larvivorous non-target species, Gambusia affinis (Cyprinodontiformes: Poeciliidae). Dimilin, applied for 24 h at a concentration of 78 ng/l, corresponding to the LD90 against the fourth instar larvae of Culex pipiens (Diptera: Culicidae) was first tested on growth and development of 7-day old juvenile mosquitofish during 45 days following treatment. Results showed that dimilin caused significant (p < 0.01) reduction in both length and weight of juveniles from days 30 following treatment, compared to controls. In a second series of experiments, designated for measurements of glutathione (GSH), adults of G. affinis were exposed continuously to a concentration of 78 ng/l for 30 days. Treatment resulted in a significant reduction in the amount of glutathione in mosquitofish bodies starting day 15 during treatment, compared to controls.

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.

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.

In vitro effects of RH-0345 and KK-42 on ecdysteroid levels and cuticle synthesis by pupal integument of mealworms

In this study, the effects of two insect growth regulators (KK-42 and RH-0345), applied either alone or in combination, were evaluated on the ecdysteroid production in vitro. Integument explants from the abdominal sternites of newly ecdysed pupae of mealworms, Tenebrio molitor, were cultured and the amounts of ecdysteroids, released into the culture medium, were determined by an enzyme immunoassay (EIA) after various intervals of incubation. In combined treatments, explants were cultured for the first two days in a medium added with the first compound and then transferred in new medium containing the second compound. EIA measurements showed that RH-0345, either alone or followed by KK-42, resulted in higher amounts of ecdysteroids as compared to controls. In contrast, KK-42 alone caused a significant reduction. But, when KK-42 was followed by RH-0345, the ecdysteroid amounts were equal to controls. In another series of experiments, the effects on cuticle secretion were examined. Only in the case that explants were treated with RH-0345, either alone or followed by KK-42, new cuticle synthesis was observed.

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.

Laboratory evaluation of dimilin on growth and glutathione activity in mosquitofish, a non-target species

Recently, dimilin was found to be effective on Culex pipiens (Diptera: Culicidae). Although considerable research has evaluated the efficacy of diflubenzuron, a benzoylphenylurea derivative, against target pest populations, impacts of this compound on nontarget organisms are comparatively unknown. Therefore, this study evaluate toxicity of dimilin (25% W.P), a trade formulation of diflubenzuron, on a larvivorous non-target species, Gambusia affinis (Pisces, Poeciliidae). The compound, applied for 24h at a concentration of 78 ng/l corresponding to the LD90 obtained against the fourth instar larvae of C. pipiens, was first tested on growth and development of G. Affinis by measuring some morphometric indexes. Results showed that dimilin caused a significant (p<0.01) reduction in both the length and the weight of juveniles. It had no significant effect on the gonadosomatic index and the condition index (K) measured in adult females. A significant reduction in hepatosomatic index was only observed at day 30 during the exposure. In addition, the body level of glutathione was also determined in order to provide information on their toxicity. Treatment resulted in a significant reduction in both the amount of ovarian proteins and the level of body glutathione starting day 15 compared to controls of the same age.

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.

Stage-specific effects of diflubenzuron on ecdysteroid titers during the development of Tenebrio molitor: evidence for a change in hormonal source

The effects of the insect growth regulator diflubenzuron (DFB) were observed on the larval-larval and larval-pupal moulting cycles of Tenebrio molitor, after treatment at ecdysis. In both cases, the first parts of the cycles, from ecdysis to apolysis, were apparently not affected, but the pharate periods were lengthened; treated animals were generally unable to perform ecdysis and died at this step. The ecdysteroid titers in the hemolymph of treated animals were measured with a radioimmunoassay and compared to controls. During larval-larval cycles, the single ecdysteroid increase was not affected by DFB treatment. On the contrary, during larval-pupal development, a significant modification was observed; whereas two ecdysteroid peaks occurred in controls, the second peak of treated animals was significantly reduced and slightly delayed; however, the first peak was not modified. Taking into account that previous observations demonstrated a complete inhibition of the ecdysteroid peak in Tenebrio pupae, these stage-specific differences could reveal either a change in the DFB sensitivity of a sole endocrine source (i.e., prothoracic gland) or a change in hormone origin during metamorphosis. Ligation experiments during the last larval stage, in combination or not with DFB applications, clearly demonstrated the change in the moulting hormone source at the end of larval development in Tenebrio.