Control of Planococcus citri (Risso) (Hemiptera: Pseudococcidae) On White Yam Variety (Pona) In Storage.
The mealybug, Planococcus citri is a very important pest of yam in storage. Six chemicals namely cypermethrin, imidacloprid, groundnut oil emulsion, soyabean oil emulsion, sunlight dishwashing detergent and key soap were evaluated in the laboratory and improved yam barns to ascertain their efficacy in the management of the yam tuber mealybug (P. citri). In the laboratory, the insecticidal effect of the chemicals was evaluated on the third instar larvae and adult P. citri by topical method. In the laboratory bioassay, mortalities were recorded at 12, 24 and 48 h and subjected to Probit analysis to obtain LD50 and LD90 values. For both stages of the pest, LD50 and LD90 decreased with longer exposure period to the six chemicals. However, for the same exposure period, the lethal dosage for the third instar larvae was lower than the lethal dosage of the adult insect for all the tested chemicals. Cypermethrin at 0.01, 0.02, 0.03 and 0.04 % concentration recorded the lowest LD50 and LD90 values for both the third instar larvae and adult stages while key soap solution at 0.125, 0.25, 0.50 and 1.00 % recorded the highest LD50 and LD90 values. The other chemicals produced intermediary LD50 and LD90 values. In the improved yam barns, cypermethrin (0.049 %), imidacloprid (0.071 %), groundnut oil emulsion (0.963 %), soyabean oil emulsion (1.231 %), sunlight dishwashing detergent (1.948 %), key soap (2.475 % ) as well as water control were applied four times (seven days apart) to the mealybug infested yams. At the second application of cypermethrin, imidacloprid and groundnut oil, there was over 95 % mortality of the P. citri which was significantly different from the mortality caused by soyabean oil, sunlight detergent and key soap solution, which caused less than 90 % death of the mealybugs. At the fourth application, all the chemicals killed all the P. citri on the tubers.