Bioassay of some Egyptian isolates of Bacillus thuringiensis against Culex pipiens (Diptera: Culicidae).

Some Egyptian isolates of Bacillus thuringiensis (BT) were grown on economic media contain 4% of fodder yeast in tap water and incubated under shaking conditions for four days. The biological activities of these isolates against Culex pipiens (Diptera: Culicidae) were carried out to determine their effectiveness against field and laboratory strains of 3rd larval instar. All isolates of BT were more pathogenic to laboratory strain. causing up to 84% larval mortality. The insecticidal activities of these isolates were extended to the pupal stage causing a significant effect on pupal mortality in both strains tested. A pronounced effect on adult emergence was noticed with remarkable adult malformations especially in the case of the isolate No. 2. The reproductivety of females was affected significantly by all isolates applied.

Biodiversity of the microbial flora associated with two strains of Culexpipiens (Diptera: Culicidae).

Bacterial Flora from external surface and alimentary canal of wild and laboratory strains of Culex pipiens were isolated and investigated using quantitative bacterial cultures. Individual colonies were subcultured and identified to species level. Counts from alimentary canal differ significantly from those of the external surface. An increase in bacterial density was detected after feeding on mammalian and avian blood meal. Bacterial identification revealed a complex bacterial flora. In addition to members of family Enterobacteriaceae species of Bacillus, Staphylococcus, Streptococcus, and Acinetobacter are the most common in both strains investigated. Gram negative bacteria were increased significantly after feeding on blood meals than those detecting during the feeding on sugar after emergence of the adult female mosquitoes and vise versa with Gram positive bacteria. Bacterial isolates were tested for resistance to the most common commercial antibiotics.

Laboratory evaluation of heavy metals stress on certain biochemical parameters of the aquatic insect, Sphaerodema urinator Duf. (Hemiptera: Belostomatidae).

The present work discussed the effect of lead and copper on certain biochemical parameters of the aquatic insect, Sphaerodema urinator, Duf. (Hemiptera: Belostomatidae). The insect samples were collected from fish farms of some volunteers. LC25 and LC50 were determined. The insects were exposed to three concentration levels (10, 20 and 30 mM) of lead nitrate and copper sulphate. The biochemical studies were carried out on the whole body homoginate. The results showed great reductions of the main metabolites (carbohydrates, lipid and protein). A decline in the alkaline phosphatase activity was detected, while an increase in the activity of acid phosphatase was found. Also the treated insects showed lower activities of GOT and GPT. In general, all estimated parameters were less than those of control.

Effectiveness of IGRS (CGA-184699) and (CGA-259205) on the respiratory metabolism of the red palm weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae).

Prepupae of Rhynchophorus ferrugineus were topically applied with one of three dose-levels (1.00, 0.10 or 0.01 microgram/insect) of lufenuron (CGA-184699) or diofenolan (CGA-259205). The daily O2 consumption and CO2-output were determined and the respiratory quotient (RQ) was calculated. Lufenuron prohibited the pupae to consume O2, regardless of their age. Considering the CO2 release, this IGR exerted an inhibitory action on pupae increasingly correlated with the increasing dose-level. Volumes of consumed O2 reversely correlated with the dose value of diofenolan. Also, CO2 output was suffered an inhibitory effect of diofenolan which was consecutively related to the dose value. An U-shaped pattern of daily respiration was not, unfortunately, attained, irrespective of the IGR or its dose. In addition, RQ mean values were less than unity but exceeded 0.7.

Insecticidal activity of selected actinomycete strains against the Egyptian cotton leaf worm Spodoptera littoralis (Lepidoptera: Noctuidae).

Actinomycete strains isolated from soil samples of Saudi Arabia and Egypt were used in the present study to investigate the biological activity of their secondary metabolites on the cotton leaf worm Spodoptera littoralis. Secondary metabolites of 41 strains were given to the newly molted last instar larvae through the food plant (Castor leaves). Many actinomycete strains (58% of all) caused larval mortality ranging from 10-60%. Treatments with strains no. 7, 36, 41 resulted in significant prolongation of larval life (10.0 +/- 1.26, 11.5 +/- 0.7 and 10.6 +/- 1.5 days Vs 9.2 +/- 0.4 of controls). Pupation was affected by the actinomycete treatments (60.1% of all). Success of pupation ranged only from 20 to 80%, depending on the efficiency of the tested secondary metabolites. In contrast, the pupal duration had not been significantly affected but 19.5% of actinomycete strains halted the pupation, because different percentages of pupal deformities were counted (100% pupal deformation after treatment with secondary metabolites of actinomycete strains no. 36). In addition, considerable lethal effect of some actinomycetes were observed on pupae (60, 42.9, 40, 50 and 66.6% pupal mortalities caused by secondary metabolites of strains: 2, 9, 16, 18 and 26, respectively). Secondary metabolites of 34.1% of all actinomycete strains blocked the adult emergence. Depending on the available data, Streptomyces and Streptoverticillum were found the most potent actinomycetes affecting the biological and physiological criteria of the present insect species.

Respiratory metabolic responsiveness during the pupal stage of the red palm weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae) to certain plant extracts.

The prepupae of Rhynchophorus ferrugineous were topically applied with one of three dose-levels (0.1, 0.005 or 0.001 microgram/insect) of Jojoba oil (Joj) or azadirachtin (Azt). The daily O2 consumption and CO2 respiratory output were determined and the respiratory quotient (RQ) was calculated. After Joj treatments, O2 consumption of early- and late pupae increased as the dose-level was decreased. The respiration curve did not assume an U-shaped pattern as common in the pupal stage of many insect species. Also, an inhibitory action of Azt on the pupal respiration has been clearly exhibited. A similar result of the respiration curve was observed by Azt. All dose levels of Joj, but only the higher two ones of Azt, suppressed the CO2 release. Both botanicals inhibited the RQ during the pupal stage. However, all RQ mean values of treated or control pupae were < 1.0 and > 0.7.

Preliminary studies on insecticidal activities of actinomycete strains propagated on solid and broth media using Musca domestica (Diptera: Muscidae).

Forty-one actinomycete soil isolates were propagated on solid media and subjected to a screening program for their insecticidal activities. These strains were studied to evaluate their efficiency as biocontrol agents against third larval instar of the house fly Musca domestica. Two groups of larvae were fed on either artificial media with the organisms studied (group I), or on artificial media inoculated with the secondary metabolites (group II). Among the strains selected for biological activity screening 15 strains of group I affected significantly the larval duration of the examined insects, compared to 18 strains of group II. This increase ranged from 7.2 +/- 0.5 to 11.1 +/- 4.2 for group I and from 7.1 +/- 0.3 to 17.5 +/- 4.81 for group II compared to 7.0 +/- 0.5 of controls. The lethal effects of some strains were recorded when the strain no 27 caused the highest mortality percentage (80%) in group I, while 55% mortality was recorded for group II using the secondary metabolites (broth media) of strain 20. In addition, many strains affected the pupal and adult stages expressing latent effects of their strains. A slight reduction in larval duration was recorded for strain 22. Streptomyces and Streptoverticillium were recorded as the most effective genera.

Effectiveness of the non-steroidal ecdysone mimic, RH-5849 for the control of Musca domestica vicina.

The new non-steroidal ecdysone mimic, RH-5849 (1, 2-benzoyl-1-tert-butylbenzohydrazine) was investigated, its biological actions were evaluated in the laboratory against a susceptible strain of Musca d. vicina. The larvae of 1-day old and of 4-day-old were fed on diets treated with different concentrations of the compound. RH-5849 shortened the larval and pupal durations and induced the initiation of premature lethal moult. The pupation rate was highly affected, where it was reduced to 46.7% at a concentration rate of 250 ppm. Also, the adult emergence was drastically blocked by the action of RH-5849 where its percentage was decreased to 42.9 at 250 ppm. In regard to the fecundity and egg viability, RH-5849 induced a cessation of oviposition in females produced from 1-day-old and from 4-day-old larvae fed on diets treated with 160 and 200 ppm, respectively. In addition, RH-5849 halted the larval and pupal growth, where the untreated pupae were generally heavier than those produced from treated larvae.