Estudos Sobre os efeitos de um produto a base de Bacillus Thuringiensis var. Kurstaki em Ephestia Kuehniella (Zeller, 1879) (Lepidoptera: Pyralidade) e no seu Ectoparasitoide Bracon hebetor (Say, 1836) (Hymenoptera: Braconidae)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

Ephestia kuehniella is a very important pest, attacking wheat flour in mills and stored places. Due to the negative impact of the chemical control methods, alternative agents are being studied to reach more safety and more satisfactory results. Some biological, physical and mechanical components should be adequate to be includes in integrated pest management programs (IPM) to reduce the injury of this lepidopterous pest. Within the biological agents, Bacillus thuringiensis var. kurstaki (Btk) and the braconid wasp Bracon hebetor are considered very efficient in controlling, separately, E. kuehniella populations. However, the insertion of these two agents in IPM programs needs some studies concerning the interaction between them and their natural pyralid host. The present study aimed to investigate the interaction between Btk and B. hebetor, in addition to evaluate their efficiency in controlling E. kuehniella. Within such a purpose some approaches were studied, such as: susceptibility of E. kuehniella larvae to Btk; chronic effects of Btk on the survived individuals; effect of diseased and survived E. kuehniella larvae on B. hebetor development; compatibility between the two biological agents and B. hebetor capacity to distinguish between healthy and diseased hosts. All experiments were conducted under controlled laboratory conditions of 25 ± 20C, 70 ± 10% R. H. and 12 hours of photophase (Department of Zoology, IB, UNICAMP). The pyralid larval susceptibility varied according to the age. The young larvae (L1) showed to be more susceptible than the old ones (L3 and L5). The CL50s were calculated as 0,05%; 0,16% and 1,77% for the first, third and fifth instars respectively. The acute as well as the chronic effects of Btk on E. kuehniella development varied according to the exposure time, age and pathogen concentration. Adults originated from survived E. kuehniella larvae did not show any biological or structural alterations, when the pathogen was applied against the first and thirdinstar larvae. On the other hand, adults originated from survived 5th instar larvae suffered reduction in their reproductive capacity. The egg viability in all these cases did not reveal any significant differences when compared with testimony block. The direct contact of Btk commercial product resulted in reduced longevity among E. kuehniella adults. Reduction in longevity was also detected when B. hebetor females were kept in contact with the same product. The braconid female parasite was able to distinguish between healthy and diseased host larvae, avoiding to attack the later. Parasitization capacity was reduced when the wasp female was able to deposit its eggs in pyralid larvae during the initial phase of the bacterial disease. B. hebetor adult longevity was reduced when parasitoid wasps were fed on honey containing Btk. Combinations between the two biological agents did not result in any synergistic effect under the conditions of the present study, and both of then could be recommended to be applied in wheat mills

ASSUNTO(S)

patologia bacillus thuringiensis controle biologico

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