M. S. Saleh

Resistance development in mosquito larvae Culex pipiens to the bacterial agent Bacillus thuringiensis var. israelensis

Abstract:  Mosquito larvae of Culex pipiens were subjected repeatedly to selection pressure with the bacterial agent Bacillus thuringiensis var. israelensis (B.t.i.) in the laboratory. Only 2.78‐fold increase in tolerance to B.t.i. was induced in C. pipiens as a result of 20 generations of selection. The tolerance of C. pipiens to B.t.i. decreased by about 58% after stopping the selection for three generations. Larval selection with B.t.i. caused a reduction in the reproductive potential of mosquito adult survivors but did not affect the adult longevity and the time of blood meal digestion ingested by female mosquitoes.

Effects of six insect growth regulators on mosquito larvae of aedes aegypti

The biological effects of six insect growth regulators (IGRs) AI3-37634-C, AI3-36877-b, AI3-37603-b, AI3-36807-b, AI3-37837-a and AI3-36809-a against immature stages and adults of Aedes aegypti have been evaluated. According to IC50 values obtained (concentration to inhibit the emergence of 50% of adults), AI3-36809-a (0.02 μg/ml) proved to be the most effective compound, followed by AI3-37603-b (0.04 μg/ml), AI3-37837-a (0.11 μg/ml), AI3-36807-b (0.17 μg/ml), AI3-37634-C (0.48 μg/ml) and AI3-36877-b (1.4 μg/ml), respectively. The results showed also that the duration of the fourth instar larvae of A. aegypti was prolonged when these larvae were exposed to the effective concentrations of the above compounds.Apart from delayed lethal action, possible effect of the compounds tested on the basal follicle numbers developed by females of A. aegypti which survived after larval treatment with IC50 of the above-mentioned compounds has been considered. Generally, the results indicate that the females treated have more follicles than the untreated ones of similar age and grown under identical conditions.RésuméLes effets biologiques de six régulateurs de croissance dans les insectes (IGRs) AI3-37634-C, AI3-36877-b, AI3-37603-b, AI3-36807-b, AI3-37837-a et AI3-36809-a sur les stades non mûrs et adultes de Aedes aegypti ont été évalués. D’après les valeurs de IC50 obtenues (concentration nécessaire pour inhiber l’émergence de 50% d’adultes), AI3-36809-a (0,02 g/ml), fut le composé le plus efficace, suivi par AI3-37603-b (0,04 g/ml), AI3-37837-a (0,11 g/ml), AI3-36807-b (0,17 g/ml), AI3-37634-C (0,48 g/ml) et AI3-36877-b (1,4 g/ml), respectivement. Ces résultats ont aussi montré que la durée de la 4ème phase des larves d’A. aegypti était prolongée quand ces larves étaient exposées aux concentrations efficaces de ces composés. Hormis l’action mortelle retardée, on a aussi considéré l’effet possible des composés testées sur les effectifs de base de follicules développées par les femelles de A. aegypti qui ont survécu après que les larves avaient été traitées au IC50 des composés mentionnées plus haut. En général, les résultats montrent que les femelles traitées ont plus de follicules que celles qui ne le sont pas quand elles ont le même âge et quand elles sont cultivées dans les mêmes conditions.

Effect of larval selection with two bioinsecticides on susceptibility levels and reproductive capacity ofAedes aegypti (L.)

Two bacterial insecticides,Bacillus thuringiensis H-14 andB. sphaericus 1593 were evaluated for larvicidal potency against mosquito larvae ofAedes aegypti. LC50 values showed thatB.thuringiensis H-14 (4×105 spores/ml) had a higher pathogenicity against fourth larval instars ofA. aegypti thanB. sphaericus (3.1×106 spores/ml) by about 7.75 times.Larval selection with LC90 of both pathogens for 8 successive generations caused a decrease in the susceptibility levels of selected strains ofA. aegypti as compared with the original strain. Moreover, the results indicated that the effect of larval selection with the above bioinsecticides led to an obvious reduction in the egg production and hatchability of eggs produced by mosquito adults that developed from surviving larvae.ZusammenfassungZwei bakterielle Insektizide,Bacillus thuringiensis H-14 undB. sphaericus 1593 wurden hinsichtlich ihrer larviziden Wirkung auf die Larven der StechmückeAedes aegypti untersucht. Die LC50-Werte zeigten, daßB. thuringiensis H-14 (4×105 Sporen/ml) wirkungsvoller gegen die L4 vonA. aegypti waren alsB. sphaericus (3,1×106 Sporen/ml), und zwar um das 7,75fache.Eine larvale Selektion mit LC90 beider Pathogene 8 Generationen hindurch, verursachte eine Abnahme der Empfindlichkeit gegenüber dem Pathogen, verglichen mit unbehandelten Stämmen. Andererseits zeigten die Ergebnisse, daß die larvale Selektion durch die beiden Pathogene zu einer beträchtlichen Verminderung der Eiproduktion und der Eischlüpfquote von Mücken, die aus überlebenden Larven hervorgingen, führte.

The delayed effects of Bacillus thuringiensis H-14 on the reproductive potential and subsequent larval development of the mosquito Culex pipiens L.

The results indicated that the reproductive potential (egg production and hatchability of eggs) of mosquito adults Culex pipiens L. survived from larval treatments with LC25, LC50 and LC75 of the bacterial agent Bacillus thuringiensis H‐14 (B.t. H‐14) was significantly reduced in the first generation but was remained unchanged in the second generation. The results showed also a reduction in the percentage pupation of larvae and adult emergence. Sex ratio and longevity of adult survivors were also affected. Larval treatments with B.t. H‐14, however, affect neither the time lapse from oviposition to adult emergence nor the time of blood meal digestion ingested by mosquito female survivors.

Factors affecting efficacy ofBacillus thuringiensis H-14 against mosquito larvae with special reference to the joint action of the pathogen with three chemical insecticides

In laboratory trials with the pathogenBacillus thuringiensis H-14 (B. t. H-14) against culicine larvae ofCulex pipiens L. andAedes aegypti (L.), the following factors significantly influenced larvicidal activity: larval instars, mosquito species, exposure time and temperature. Variation in water pH, however, did not significantly affected efficacy.Different levels of potentiation and additive effects were also obtained when the bacterial agentB. t. H-14 applied jointly with the chemical insecticides malathion, dursban and fenvalerate against mosquito larvae.ZusammenfassungBei Laborversuchen mit dem PathogenBacillus thuringiensis H-14 (B. t. H-14) zur Bekämpfung der Larven vonCulex pipiens L. undAedes aegypti (L.) beeinflußten folgende Faktoren in signifikanter Weise die Wirkung des Pathogens: Larvenstadium, Stechmückenart, Anwendungszeit und Temperatur. Dagegen zeigte der pH-Wert keinen gesichrten Einfluß.Bei Kopplung vonB. t. H-14 an je eines der chemischen Insektizide Malathion, Dursban und Fenvalerat ergaben sich potenzierende und additive Effekte.

Controlled-release malathion formulations as mosquito larvicides

Three polyvinyl chloride (PVC) formulations of malathion were prepared and tested as controlled-release formulations against mosquito larvae of Culex pipiens L. Non-expanded formulations gave effective control, with 100% larval mortalities, for 23–51 days, followed by expanded (16–33 days) and foamed (14–27 days) formulations. The results indicate that increasing the percentage of active ingredient in the present formulations increased their effective control against mosquito larvae for longer periods.Larval treatments with these formulations of malathion led apart from lethal action to a decrease in the reproductive potential and in longevity of mosquito adults which survived from these treatments.RésuméTrois polyvinyl chloride (PVC) formulations de malathion ont été préparées et expérimentées comme formulations a débit contrôlé contre les larves du moustique Culex pipiens L. Les résultats ont montré que les formulations non dilatées ont donné un contrôlé efficace avec 100% de mortalité des larves pour 23–51 jours, suivi par des formulations dilatées (16–33 jours) et des formulations gonflées (14–27 jours). Les résultats ont aussi indiqué l’augmentation du pourcentage de l’ingrediant actif dans les présentes formulations a sugmenté leur contrôlé efficace sur les larves des moustiques pour de plus longues periodes.Hormis leur action mortelle, le traitement des larves avec ces formulations de malathion, a aboutit à un effet décroissant sur le potentiel de reproduction, ainsi que sur la longévité des moustiques adultes qui ont survécu a ce traitement.

Sustained-release formulations ofBacillus thuringiensis serotype H-14 and plastic formulations of Abate for long-term control of mosquito larvae

The larvicidal activity of sustained-release formulations ofBacillus thuringiensis H-14 (Bactimos briquets) and controlledrelease plastic formulations of Abate against mosquito larvae ofAedes aegypti (L.) has been evaluated. The test formulations provided continuous effective control with 90–100% larval mortality for several weeks.The presence of suspended soil constituents was associated with a lowering of larval mortality and tended to reduce the durations of effective control of Bactimos and Abate plastic pellets against mosquito larvae by about 1.8 and 2.2 times, respectively.Treatments with such formulations did not appear to prevent hatch of eggs which oviposited after application, but all newly hatched larvae failed to develop beyond the second instar.ZusammenfassungEs wurde die larvizide Aktivität von im Wasser ausgebrachten, brikett-gebundenen Formulierungen vonBac. thuringiensis H-14 (Bactimos)_sowie pellet-gebundenen Formulierungen von Abate gegen die Larven vonAedes aegypti (L.) untersucht. Die getesteten Formulierungen ermöglichten eine wirksame Bekämpfung mit 90–100% Larvenmortalität für mehrere Wochen.Die Anwesenheit von im Wasser schwebenden Bodenbestandteilen war mit einer Verringerung der Larvenmortalität verbunden und reduzierte die Wirkungsdauer von Bactimos bzw. Abate um das 1,8-bzw. 2,2fache.Die Anwendung solcher Formulierungen konnte das Schlüpfen der nach der Applikation abgelegten Eier zwar nicht verhindern, doch waren alle geschlüpften Larven außerstande, sich weiter als bis zur L2 zu entwickeln.

Use of plastic formulations of chlorpyrifos and sumithion as mosquito larvicides and their delayed effects on the basal follicle numbers developed by female survivors

Tests were conducted to evaluate the larvicidal effectiveness of three controlled-release plastic formulations of both chlorpyrifos and sumithion against mosquito larvae ofCulex pipiens. Excellent control with 90–100% larval mortality was achieved for 85, 77, 73, and 64, 54, 48 days posttreatment by using the non-expanded, expanded and foamed formulations of chlorpyrifos and sumithion, respectively.Apart from lethal action, larval treatments with the above formulations led to an increase in the mean number of basal follicles developed by mosquito females which survived from these treatments. The increase in this mean per female was in respect 23.4, 30.0, 18.7% in case of chlorpyrifos formulations, and 21.8, 17.2, 26.8% in case of sumithion formulations.ZusammenfassungDrei granulierte (Plastik)-Formulierungen von Chlorpyrifos und Sumithion ergaben gegenCulex pipiens-Zweitlarven 90–100% Mortalität, beim erstgenannten Wirkstoff nach 73–85 Tagen und beim zweitgenannten nach 48–64 Tagen.Außer dieser Letalwirkung zeigte sich bei überlebendenCulex-Weibchen eine Zunahme der Zahl der Basalfollikel und zwar bei Chlorpyrifos um 18,7–30,0% und bei Sumithion um 17,2–26,8%.

The biological effects of three insect growth regulators onCulex pipiens L

Tests were made to determine the possible juvenilizing effects of three insect growth regulators (IGRs) namely, IKI 7899, SIR 8514 and Dowco 439 on immature stages and adults ofCulex pipiens L. using the IC50 values (concentration to inhibit the emergence of 50% of adults) as a criterion. The results indicated that IKI 7899 (0.00031 μg/ml) proved to be the most effective compound followed by SIR 8514 (0.0052 μ/ml) and Dowco 439 (0.029 μg/ml).Apart from lethal action, treatment of fourth larval instars with the IC25 values (concentration to inhibit the emergence of 25% of adults) of the above-mentioned IGRs affected the reproductive capacity of surviving adults. Moreover, larval treatments with these compounds led to a marked prolongation in the duration of first gonotrophic cycle. There was also an increase in the proportion of survived females/males ofC. pipiens after these larval treatments.ZusammenfassungEs wurden Versuche durchgeführt, um die möglichen Juvenilisierungswirkungen von 3 Insekten-Wachstumsregulatoren (IGRs), nämlich IKI 7899, SIR 8514 und Dowco 439, auf die Larven und Adulten vonCulex pipiens L. kennenzulernen, wobei die IC50-Werte (Konzentration bei welcher 50% der Adulten sich nicht häuten) als Kriterium verwendet wurden. Die Ergebnisse zeigen, daß IKI 7899 (0,00031 μg/ml) am wirksamsten war, gefolgt von SIR 8514 (0,0052 μg/ml) und Dowco 439 (0,029 μg/ml).Abseits von dieser Letal-Aktion senkte eine Behandlung der L4 mit den IC25-Werten (Konzentrationen, welche bei 25% der Adulten Häutungshemmung verursachen) die Vermehrungskapazität der überlebenden Adulten. Darüber hinaus führte die Behandlung der Larven mit diesen Verbindungen zu einer wesentlichen Verlängerung der Dauer des 1. gonotrophischen Zyklus. Auch zeigte sich ein Ansteigen des Anteils überlebender Weibchen vonC. pipiens nach diesen Larvenbehandlungen.

Formulations for controlled-release of fenitrothion in water

Laboratory evaluations were conducted for 94 weeks to compare, under static conditions, residue levels maintained in water treated with three polyvinyl chloride pellet formulations of fenitrothion. The results showed that foamed formulation (polyvinyl chloride + dioctyl phthalate + Triton X-100 + ammonium carbonate + citric acid + water + fenitrothion) gave the highest rates in the percentage of fenitrothion released followed by expanded formulation (polyvinyl chloride + dioctyl phthalate + Triton X-100 + fenitrothion), while non-expanded formulation (polyvinyl chloride + dioctyl phthalate + fenitrothion) gave the least.The records indicated that increasing both the exposure time of formulations tested into the water and the percentage of active ingredient in the present formulations increased the amount of fenitrothion released from these formulations. However, all tested formulations gave low-initial rate of release.The results showed that there were two rates of release of fenitrothion. In the first step, the non-expanded formulation gave a slow rate of release, expanded formulation gave a moderate rate of release, and foamed formulation gave a fast release. In the second step, the release rate of fenitrothion was slow for all tested formulations.RésuméLes évaluations faites au labouratoire durant 94 semaines pour comparer sous des conditions satables des niveaux résiduels maintenus dans l’eau traitée avec trois polyvinyl chloride formulations de fenitrothion. Les resultats ont montre que les formulations gonflées (polyvinyl chloride + dioctyl phthalate + Triton X-100 + ammonium carbonate + citric acid + eau + fenitrothion) ont donné les plus hauts degrés dans les pourcentages du fenitrothion detaché suivi par des formulations soit dilatées (polyvinyl chloride + diocytyl phthalate + Triton X-100 + fenitrothion), et non dilatées (polyvinyl chloride + dioctyl phthalate + fenitrothion). Les resultats ont indiqué que l’accroissement de deux du temps de le exposition de la formulation dans l’eau et le pourcentage de la matière active dans les formulations ont augmenté la quantité de la fenitrothion detachée.Les resultats ont montré qu’il y a deux degrés de détachements de fenitrothion. Dans la première étape, la formulation non dilatée donna un degré lent de détachement tandis que la formulation dilatée donna un degré modéré de detachement et la formulation gonflee donna un degré rapide de détachement. En deuxième étape, toutes les formulations ont donné un degré lent de détachement.