|July 2003. Mealybugs (thought at first to be scales), as seen on these unripe papaya fruit, are causing serious damage at the Pacific Adventist University commercial farm outside Port Moresby, Papua New Guinea. The farm manager is concerned, especially as spraying with synthetic insecticides has not helped. Some natural enemy (predators – ladybirds and parasitoids – hymenopterans) are present, but are not having much effect on the booming population. The farm depends heavily on synthetic insecticides for the control of pests. Can anyone identify the mealybug and give some insight into control measures.
The images are not sufficiently clear to be sure, but they look like mealybugs (whose waxy coverings make pesticide use relatively ineffective unless the chemical is systemic). The sudden problem suggests this is an alien species that has been introduced without appropriate natural enemies, which would make it a good candidate for classical biological control. For that, authoritative identification is needed.
A likely candidate species might be Paracoccus marginatus from Central America; it recently got into Micronesia (Guam & Palau) and can be damaging on papaya. The insects should be put in 70% ethanol and shaken to wash off the wax; the bodies of P marginatus appear yellow initially, but turn black within 24 hours at room temperature. On the other hand, if the tube is stood in recently boiled water for 20 minutes immediately after the insects are killed, the bodies do not go black.
However, this is not absolutely diagnostic. Send a heat-treated sample in 80% ethanol to the Insect Information Service, Natural History Museum, London, for identification.