Investigation of Insecticidal Activity of Different Microbial Fertilisers on Diamondback Moth, Plutella xylostella L. (Lepidoptera: Plutellidae) Under Laboratory Conditions

The diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) is one of the most destructive plant pests of the Brassicaceae family in worldwide. Frequently used synthetic insecticides leads to the development of resistant populations of the diamondback moth to various insecticides, with adverse effects on humans and the environment. Microbial fertilisers contain beneficial microorganisms that promote plant growth and increase soil fertility. Some microbial fertilisers may contain entomopathogenic fungi, bacteria or viruses that have a direct lethal effect on insects. The aim of the study was to determine the insektisidal effect of GBF-41 (Bacillus mojavensis) and RC-72 (Bacillius subtilis) microbial fertilisers on different larval developmental stages and pupal weights of diamondback moth. Diamondback moth larvae reared as colonies on natural hosts in the laboratory were used in this study. Microbial bacteria solutions were incubated at 28°C at 150 rpm for 3 hours. Blotting papers were placed on the bottom of a 9 cm petri dish then 3x5 cm discs were cut from broccoli leaves then 100 μl of microbial fertiliser was transferred by a micropipette and distrubuted on the leaf with no gap. The larvae having I, II, III and IV instars were starved for 3 hours then 20 larvae were transferred to each petri dish. Treatments were carried out as each petri dish as a replication having 3 replication. Distilled water was used as control. Trials were checked daily and immobilised larvae were recorded as dead. The data obtained were analysed by LSD test using SAS software. Survival curves were generated by Kaplan Meier test using SigmaPlot statistical software. The difference between microbial bacteria solutions was compared by Long-Rank test. There was no statistical difference between the mortality of I, II and III. instars. Larval mortality in IV. instar was 13.33±1.15 and 6.00±1.00 in RC-72 and GBF-41 microbial fertilisers, respectively. Pupal weights were recorded as 2.61±1.98 mg, 5.68±0.51 mg and 6.20±0.65 mg in RC-72, GBF-41 and control, respectively. The difference between the survival rates of IV. instars in RC-72 and GBF-41 microbial fertilisers was significant (Log-Rank test; Chi-square= 6.949; df=1, P<0.01). In conclusion, tested microbial agents used as an alternative to the sustainable and environmentally friendly control of diamondback moth could be an effective method on larval mortality, pupal weights and survival rates of the pest.