Abstract
The control of Acromyrmex leaf-cutting ants is necessary due to the severe damage they cause to diverse crops. A possibility was to control them using the bacterium Bacillus thuringiensis (Bt) that characteristically produces insecticidal crystal proteins (ICPs). The ICPs have been effective in controlling lepidopterans, dipterans, and coleopterans, but their action against hymenopterans is unknown. This paper describes an attempt to isolate Bt from ants of two Acromyrmex species, to evaluate its pathogenicity towards these ants, and to test isolates by PCR. Bacterial isolates of Bt obtained from A. crassispinus and A. lundi have been assayed against A. lundi in the laboratory. The bioassays were carried out in BOD at 25 degrees C, with a 12-hour photoperiod, until the seventh day after treatment. The Bt isolates obtained were submitted to total DNA extraction and tested by PCR with primers specific to cry genes. The results showed Bt presence in 40% of the assessed samples. The data from the in vivo assays showed a mortality rate higher than 50% in the target population, with the Bt HA48 isolate causing 100% of corrected mortality. The PCR results of Bt isolates showed a magnification of DNA fragments relative to cry1 genes in 22% of the isolates, and cry9 in 67%. Cry2, cry3, cry7, and cry8 genes were not detected in the tested samples, and 22% had no magnified DNA fragments corresponding to the assessed cry genes. The results are promising not only regarding allele identification in new isolates, but also fort the assays aimed at determining the Bt HA48 LC50's, which can eventually be applied in controlling of Acromyrmex leaf-cutting ants.
Highlights
The ants of Acromyrmex genus, known as leaf-cutting ants, are responsible for damage to several crops (Diehl-Fleig, 1995)
Bacillus thuringiensis (Bt) produces proteins or endotoxins with highly biopesticide effects on certain representative insect species among the orders Lepidoptera, Diptera, and Coleoptera (Höfte & Whiteley, 1989; Schnepf et al, 1998). These proteins are coded by cry genes, which have all been detected in Bt isolates through the polimerase chain reaction – PCR (Juárez-Pérez et al, 1997; Hansen et al, 1998)
Bt analysis by PCR: Bt isolates obtained from A. crassispinus and A. lundi were cultivated on nutrient agar (Oxoid, UK) at 30°C for about 12 hours and submitted to total DNA extraction according to the method described by Hansen & Hendriksen (2001)
Summary
The ants of Acromyrmex genus, known as leaf-cutting ants, are responsible for damage to several crops (Diehl-Fleig, 1995). Isolation and gene analysis by PCR of the Bt isolates from ants of Acromyrmex genus was the goal of this experiment. The present work aims at adapting an appropriate bioassay method to leaf-cutting ants and applying it in pathogenicity assays of the new isolates.
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