Phytosanitary Irradiation Against Cocoa Mealybug Exallomochlus hispidus (Morrison) (Hemiptera: Pseudococcidae) on Mangosteen Fruits

The cocoa mealybug Exallomochlus hispidus (Morrison) is a quarantine pest on mangosteen. Gamma irradiation is a possible phytosanitary control treatment. This research investigated the lethal and sublethal gamma irradiation doses for controlling Exallomochlus hispidus (E. hispidus) and the impact of irradiation on mangosteen fruit quality. Methodology: Nymphs and adult females of E. hispidus were exposed to gamma irradiation (50-2000 Gy and a control) and newly emerged females were exposed to a sublethal dose of 50-400 Gy. Mangosteen fruit was irradiated at 250-1000 Gy. Reproductive development, longevity and fecundity of irradiated females were observed. The physical and chemical qualities of irradiated fruit were assessed. Results: The LD99 for the first, second and third instar nymphs and adults were 423.7, 1026.0, 1276.0 and 1934.5 Gy, respectively. Irradiation doses of 50-400 Gy on adult females resulted in significantly longer pre and post birth periods but shorter birth period. These doses also increased the longevity and decreased the fecundity, observed as 99.7% unhatched eggs and 0.3% undeveloped nymphs. The quality of mangosteen fruit did not effect by irradiation unless the red color retain and vitamin C content of fruit was significantly decreased. Conclusion: The result indicates that irradiation is an effective phytosanitary treatment to control E. hispidus on mangosteen. Irradiation doses of 250 Gy are recommended for phytosanitary treatment without degradation of fruit quality.

Key words : Irradiation treatment, LD99, mangosteen quality, ovoviviparous mealybug, quarantine pest