Parasites and predators of the meal moth Plodia interpunctella Hbn. as affected by Bacillus thuringiensis Berl.

Abstract

The interaction between Plodia interpunctella Hbn., parasites and predators and Bacillus thuringiensis Berl. has been investigated. Experiments with the parasite Bracon brevicornis Wesm. previously fed during the larval instar on treated host larvae of P. interpunctella, showed significant reduction in the egg production. The egg incubation and larval duration of the parasite were not affected except at the highest concentration (500 μg). Percentage of formed cocoons was significantly reduced at all tested concentrations. The longevity of either sex, on the other hand, was also reduced. The percentage of hatching among the deposited eggs, significantly decreased with the increase of the concentration. Investigations with adult parasite fed on treated honey solution showed a significant reduction in the number of eggs deposited, hatching among the deposited eggs, percentage of formed cocoons, the percentage of adult emergence and the longevity of the female parasite, was also reduced with the increase of concentrations. With respect to the predator Xylocoris flavipes (Reuter), it was found that the number of consumed host larvae of P. interpunctella by nymphs of the predator decreased with the increase of the concentration of δ‐endotoxm present on the larval food. The nymphal duration was prolonged as the concentration increased from 32–500 μg/g of diet. On the other hand, the longevity of male predator was shortened while that of female was not affected. The consumption of prey larvae by one couple of the predator was reduced only at higher concentrations (250–500 μg). The egg production and hatchability of eggs were also reduced. Studies with the adult stage of the predator showed similar effects with respect to the longevity of the female adults. Also the average consumption of one couple was reduced and an obvious effect on egg production was detected but in varying degrees correlated with the concentration. The hatching of eggs increased as the concentration used decreased. Zusammenfassung Wirkung von Bacillus thuringiensis Berl. auf Parasiten und Predatoren von Plodia interpunctella Hbn. Es wurden die Beziehungen zwischen Plodia‐Parasiten und ‐Predatoren einerseits und Behandlungen der Plodia‐Larven mit Bacillus thuringiensis andererseits untersucht. Experimente mit der Schlupfwespe Bracon brevicornis Wesm., die als Larve in Plodia parasitierte, zeigten eine signifikante Verringerung der Eiprodukten. Die Ei‐ und Larvenentwicklung des Parasiten wurden nur durch Behandlung der Plodia‐Larven mit der höchsten B. thur.‐Konzentration (500 ug) beeinflußt. Die Kokonbildungs‐Quote wurde bei allen Konzentrationen signifikant verringert. Auch wurde die Lebensdauer beider Geschlechter gesenkt. Das Schlüpfprozent der abgelegten Eier wurde mit zunehmender B. thur.‐Konzentration reduziert. Untersuchungen an adulten Parasiten, die mit behandelter Honiglösung gefüttert waren, zeigten mit zunehmender Konzentration signifikante Verringerungen der Zahl abgelegter Eier, der Eischlüpfquote, der Kokonbildungsquote, der Ad...

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