Function and insecticidal activity of bacteria associated with papaya mealybug, Paracoccus marginatus Williams & Granara de Willink (Hemiptera: Pseudococcidae)

This study isolated and determined the functional characteristics of bacterial flora associated with mealybug (Paracoccus marginatus) and their application as a bio-control agent. Second and fourth nymphal instars of the papaya mealybug were used for the isolation of the bacteria. These isolates were assessed for chitinolytic, protease, and glutathione S-transferase (GST) activities as well as mealybug wax degradation. Anin vitroexperiment was conducted with the most efficient isolates to control mealybugs reared on potato plants. A total of 102 bacterial isolates were obtained from the second (50 isolates) and fourth nymphal (52 isolates) stages of papaya mealybug. From these, 33 isolates were positive for chitinolytic activity, 25 isolates for protease, and 29 isolates showed glutathione S-transferase (GST) activity. In addition, 21 isolates were able to utilise mealybug wax as a carbon source. Regarding nutritional significance, the bacterial isolates exhibited nitrogen fixation, sulfur oxidation, as well as phosphate, zinc, and silica solubilisation. The application of bacterial isolates,Bacillus cereusPYP3,Bacillussp. PLB1 andSerratia marcescensFLGB16 exhibited the highest mortality rates of 78.7%, 74.0%, and 69.3%, respectively on the second nymphal stage of papaya mealybug. Mealybug associated bacteria showed significantly higher mealybug mortality compared to antibiotics (kanamycin, carbenicillin, and spectinomycin) and commercial chemicals (profenophos and chlorpyrifos) used in this study. These efficient bacterial isolates may have the potential to control the mealybug under field conditions.