Preliminary assessment of insecticidal activity of Moroccan actinobacteria isolates against mediterranean fruit fly (Ceratitis capitata)

Abstract

Microbial insecticides are considered as the most sustainable and ecologically acceptable means of crop protection. Here we report the ability of some Moroccan actinobacteria isolates to produce larvicidal compounds against the Medfly (Ceratitis capitata Wied.). Thus, actinobacteria isolates were tested for their insecticidal activity through biological and chemical screening. The primary biological screening using the brine shrimp bioassay showed that 12 isolates out of 210 (5.71%) have been found to be highly toxic at the concentration of 100 µg mL^-1. Among these, isolates OS46, 37 and B62 were the most toxic with an LC₅₀ of 0.26, 0.34 and 0.84 µg mL^-1, respectively. The freeze-dried fermentation of the selected isolates showed moderate to high insecticidal activity against the first instar larvae of C. capitata, and the most important pupation reduction was obtained for isolates 37 and B89 (0 and 6% of pupation, respectively). The chemical screening on thin layer chromatography of the crude extract of the most important isolates using specific insecticide family’s reagents showed a variety of compounds depending on isolate with at least one active spot for each tested specific reagent. Finally, the inhibition of acetylcholinesterase activity test was carried out in order to assess the possible nature of insecticidal activity of selected isolates. The obtained results show that, except the isolate 37 which probably acts by a different mode of action, all other isolates were active. This finding could have an applicative value for the potentiality of utilizing Moroccan actinobacteria isolates as an alternative to chemical insecticides in pest management mainly against C. capitata.
 
Key words: Moroccan actinobacteria, insecticidal activity, biological screening, chemical screening, <i>Ceratitis capitata</i>