SELECTION-DRIVEN ADAPTIVE RESPONSESINDROSOPHILA MELANOGASTER EXPOSED TOMETARHIZIUM ANISOPLIAE STRAIN ME1
Author: Paschalis Giannoulis
Paschalis Giannoulis: Department of Agriculture, Faculty of Agricultural Sciences, University of Patras, New Buildings, 30200 Missolonghi, Greece.
ABSTRACT
Drosophila melanogaster was exposed to repeated applications of the entomopathogenic fungus Metarhizium anisopliae strain ME1 through both non-induced and induced exoskeleton contact. This study examines the development of transgenerational host resistance to M. anisopliae. After four generations, D. melanogaster expressed high levels of larval and adult resistance against M. anisopliae strain ME1. Without further selection a decline in resistance occurred over the next three generations. Resistance was re-established following two further selected generations. Resistant population adults were larger than parental adults at equivalent densities. Initially, all three fungal doses (10⁶, 10⁷, 10⁸ sp/ml) significantly reduced larval emergence compared to controls. Some insects failed to pupate and/or emerge as adults in treated populations. Survived adult population expressed sensitivity to ether anesthesia and low levels of oviposition. Following the fourth selection round (inoculum: 10⁹ sp/ml), where few insects failed to emerge and develop normally, selection was discontinued from generations 5-9. Generations 5-7 were subsequently used to assess D. melanogaster susceptibility to M. anisopliae at larval and adult stages in both selected and wild-type lines. Adults from both lines were weighed, and selected individuals regained resistance by the 11th generation. Resistance of D. melanogaster against repetitive applications of M. anisopliae induced bigger size adult individuals to overcome the microbial pressure. Overuse of microbial insecticides has the potential to lead into losses in microbial and biological pest management tactics, increasing chemical insecticide approach to suppress pest populations.
Keywords: Entomopathogenic fungi; insecticide resistance; insect body size.