Toxicity of green silver nanoparticles of plant extracts against citrus mealybug Planococcus citri

Abstract

Planococcus citri is an economically important polyphagous insect pest and is a serious threat to horticultural crops especially mango and citrus. It is mainly controlled by synthetic insecticides which have deleterious effects on humans, livestock and environment. To dispense with the detrimental consequences of insecticides, plant extracts and their silver nanoparticles can be potential alternatives. The present study reports the effectiveness of four plant extracts and their silver based nanoparticles against P. citri. All the plant extracts and their silver nanoparticles caused mortalities of 2nd and 3rd instars of P. citri at all concentrations and exposure durations. The ginger extracts and their silver nanoparticles caused maximum mortality of 2nd and 3rd instars of P. citri (94 and 90% respectively) at the highest concentration after 72 hours followed by neem extracts and their silver nanoparticles. Similarly, the mortalities caused by garlic silver nanoparticles followed the similar pattern. Eucalyptus plant extracts and their silver nanoparticles were found to be the lease effective. It was also observed that with an increase in concentration and exposure period, the mortality also increased showing a direct relationship. Ginger plant extract and their silver nanoparticles gave the best results and lowest LC50 values by a large margin. Neem extracts ranked second followed by garlic and eucalyptus and gave significantly poor results as compared to the first two plants. The required concentration for killing 50% of the nymphal population was observed to decrease with the passage of time.