Applications of Pseudomonas spp., as a biopesticide to control Dactylopius opuntiae (Cockerell) (Hemiptera: Dactylopiidae)

Mohamed El Aalaoui and Mohamed Sbaghi

Background and Objective: Dactylopius opuntiae (Cockerell) is a major pest of Opuntia spp., cactus worldwide. This study was conducted to evaluate the efficacy of six Pseudomonas spp., isolates in managing this pest. Materials and Methods: The cochineal adult female was used for the isolation of the isolates. In the laboratory bioassays, insecticidal and repellent activities were evaluated. The insecticidal activity test evaluated four concentrations of bacterial suspensions: 0 (control), 10³, 10⁶, 10⁸ and 10¹⁰ CFU mL^–1 against first instar nymphs and adult females of the cochineal, whereas only 10¹⁰ CFU mL^–1 concentration of three isolates (EL01SB, EL02SB and EL03SB) that exhibited the highest insecticidal activity was used for the repellent bioassay. Results: The EL01SB, EL02SB and EL03SB isolates at 10¹⁰ CFU mL^–1 were the most virulent, causing the highest mortality in nymphs and adult females (92%, 88% and 76%, respectively (nymphs) and 87%, 83% and 71%, respectively (adult females)) after 6 days of exposure. Repellent activity was the highest with EL01SB isolate which exhibited a repellency index value of 75.1% at 24 DAT. Under greenhouse conditions, only the three isolates (EL01SB, EL02SB and EL03SB) were tested and isolates EL01SB (79.8% mortality) and EL02SB (64.7% mortality) at 10¹⁰ CFU mL^–1 showed significantly higher mortality and high potential for degradation of the protective wax. Regarding the functional mechanism of action, all three isolates produced chitinase, cellulase and protease and only EL01SB was found to be able to fix atmospheric nitrogen. Conclusion: The results of this study indicated that isolate EL01SB could be included in the integrated pest management approach against D. opuntiae.

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