Mahmoud Hafez

Bacillus thuringiensis affecting the larval parasite Meteorus laeviventris Wesm. (Hym., Braconidae) associated with Agrotis ypsilon (Rott.) (Lep., Noctuidae) larvae

The effect of the pathogen Bacillus thuringiensis on the larval parasite Meteorus laeviventris, associated with Agrotis ypsilon, was studied. The biology of the parasite showed to be affected in some aspects when its host larvae were fed on a diet containing B. thuringiensis. A significant reduction in reproductive potential and longevity occurred together with retardation in development. The effect of the exotoxin (thuringiensin) on the parasite has been also demonstrated.

Evaluation of adjuvants for use with Bacillus thuringiensis against Heliothis armigera (Hiibn.)

In search for adjuvants that may enhance the effectiveness of Bacillus thuringiensis against Heliothis armigera, soybean oil, soybean flour, corn flour, cottonseed flour, ground chick peas were found to improve the efficacy of the endotoxin of Bacillus thuringiensis var. kurstaki HD‐I. Bait formulations containing cottonseed kernels extracted with ethanol and hexane‐water were effective as well against the same species. The effect increased with the increase in the concentration of the bait from 2 to 10%. Variations in the concentration of raffinose, corn extract or cottonseed oil in these baits caused no changes in the efficacy of the pathogen. Sucrose, maltose and lactose, also caused an increase in the potency of the pathogen in varying degrees, but sucrose was the most effective.

Biology of hippobosca longipennis (fabricus, 1805) in Egypt (Dipteria: Hippoboscidae)

Abstract Emergence of the adult flies took place mainly between 7 and 9 a.m. The feeding mechanim was described. The prefeeding period varied from several seconds to 30 minutes. The duration of a complete blood meal took, on average, 8 minutes, and adults had to take a blood meal at least every 6 hours. The weight of the blood meal taken by newly emerged flies was 2.56 mg and 3.35 mg in males and females, respectively. The flies starvation more easily in moist than in dry atmosphere, and newly emerged flies in the laboratory were more tolerant to starvation that were flies collected in the field. Female flies were less affected by starvation than males. Male and female flies reached sexual maturity after 8 and 5.40 days, respectively, and sex ratio was 43.96% males and 56.04% females. The act of mating was described. The duration was 12 minutes. The period epapsing between two successive larvipositions was determined during August (3.6 days), November (4.1 days), February (6.4 days) and May (3.9 days). The third larval stage was described. The mean adult longevity in August was 41 and 45,6 days in males and females, respectively, whereas in February it was 56.6 and 64.9. The number of larvae laid per female was 8.2 in August and 8.7 in February. The external morphology of the pupa was described. The effect of adult food on the pupal size and weight was tested. The maximum pupal period under insectary conditions was of the larvae laid during the 4th week of November (142 days) and the minimum was for the larvae laid during the fourth week of June of the second week of July (19 days). The effect of temperature on the pupal duration was described. The shortest duration (18.8 days) occured at 32°C, while the longest (130.1 days) was at 20°C. No emergence occured at temperatures above 32°C. Study of the effect of relative humidity on the pupal duration revealed that 40% humidity was the optimum for pual development. The mean duration of pupal produced by flies reared on guinea pigs was slightly longer (20.54 days) than those obtained from flies reared on dogs (20.08 days).

A biochemical approach to potentiate the activity ofBacillus thuringiensis against corn borers

Due to the fact that the persistence ofBacillus thuringiensis (B.t.) is very short in the field as affected by exposure to ultraviolet radiation, some biochemical approaches have been adopted in an attempt to increase potentiation of the pathogen against the two lepidopterous corn borers,Chilo agamemnon andOstrinia nubilalis. These approaches were based on the incorporation of some selected non-toxic chemical compounds with different modes of action with the endotoxin ofB.t. fed to the larvae and thus resulting in its potentiation.Among the compounds tested, some representatives of inorganic salts, organic acids, protein and lipid solubilizing agents, amino acids and amides showed an obvious potentiation to the endotoxin activity against the target insects. Inorganic salts, such as, calcium oxide, calcium carbonate, zinc sulphate and potassium carbonate at 0.1% potentiated the activity of the product Dipel 2X (B.t. var.kurstaki) against the two tested species in varying degrees. With regard to protein solubilzing agents, urea, sodium thioglycollate and EDTA enhanced the potency ofB.t. againstO. nubilalis with a fold increase of 1.4–2.3. The lipid emulsifying agent Tween 80 (0.5%), caused 1.3 fold increase in the potency ofB.t. With respect toC. agamemnon, sodium thioglycollate and EDTA (0.1%) were effective in potentiating the activity ofB.t. with fold increase of 3.1 and 1.2, respectively, while urea caused a decrease in the potency ofB.t as compared with the control. The lipid emulsifying agent Tween 80 (0.5%) caused 1.3 fold increase in the potency ofB.t. The potentiating effect of aromatic compounds is not obvious with respect to the tested insect species. With amino acids and amides, it appears that some of the tested compounds enhanced the potency ofB.t. against the tested insect species but in varying degrees. The mode of action of the tested compounds has been discussed in the light of the results obtained.

Developmental stages of Agrotis ypsilon Hufn. (Lep., Noctuidae) as affected by Bacillus thuringiensis Berl.

The prepupal and pupal stages of A. ypsilon were affected by B. thuringiensis when sprayed or kept in the soil treated with the pathogen. The emerged moths showed a short longevity associated with low egg production and low fertility. B. thuringiensis showed an increased effect on the pupae when treatment was applied immediately after pupation. The effectiveness of B. thuringiensis against the moths and eggs of A. ypsilon have been also demonstrated. The longevity, egg production and fertility were significantly affected when the moths were fed on a diet containing the pathogen at certain concentrations. Also, moths released on castor oil plant sprayed with B. thuringiensis (1000 and 500 μg/ml of Dipel 2X) showed a reduced egg production and fertility. Sucrose diets containing spores of B. thuringiensis only or without viable spores (UV irradiated B. thuringiensis solution) caused adverse effects on the longevity, egg production and egg hatching, but with reduced moth mortality. Egg masses sprayed with B. thuringiensis hatched normally, but the survival of the hatched larvae was reduced when treatment was made shortly before egg hatching. Based on these results, B. thuringiensis showed a promising effect in the control of the moths A. ypsilon and may serve as an ovicide‐larvicide agent.

Activity ofBacillus thuringiensis isolates on the corn borers,chilo agamemnon Bles. (Crambidae) andOstrinia nubilalis Hbn. (pyraustidae)

The potential activity of different varieties ofBacillus thuringiensis was evaluated against the second instar larvae of the two lepidopterous corn borersChilo agamemnon andOstrinia nubilalis. Data on the LC50, slopes, 95% confidence limits and potencies of the tested varieties were determined. WithO. nubilalis, Dipel 2X (Bacillus thuringiensis. var.kurstaki HD-1) was the most potent and the LC50 was 2.68 μg/g diet. The LC50 for other varieties ranged between 3.12 and 31.95 μg/g. In the case ofC. agamemnon, the lowest LC50 was also determined with Dipel 2X being 3.68 μg/g diet; this ranged between 6.2–15.11 μg/g for other tested varieties.

The potential of the predatorOrius albidepennis onAgrotis ypsilon as affected byBacillus thuringiensis

The relation between the pathogenBacillus thuringiensis and the predatorOrius albidepennis (Hem.: Anthocoridae) associated with the greasy cutwormAgrotis ypsilon (Lep.) has been investigated.The biology of the predator showed to be affected in terms of nymphal duration, rate of food consumption and egg production when the predator larvae were fed on treated eggs or neonate larvae of the host (A. ypsilon). The effect of B-exotoxin (thuringiensin) on the predator has been also demonstrated.