We have these black beetles that are infesting our mangoes and causing them to crack open when green and they are also on our papayas. They like to rest on the underside of our coconut fronds.
Thank you for submitting your question to us and including the photographs. We have researched your problem and have determined possible causes of your infestation and damaged fruit.
There are two different pests at work in your garden. The first is the oriental fruit fly and the second is the oriental flower beetle.
The adult oriental fruit fly lays its eggs in the flesh of fruit and vegetables. The eggs hatch and the larvae (maggots) feed on the inside of the fruit. The fruit fly attacks at any stage of the fruit’s growth and ripening. The maggots feeding on the inside of the fruit cause a breakdown of tissue and internal rotting. The compromised and rotting fruit attracts the oriental flower beetle. The fruit fly maggots eventually fall out of the fruit and onto the soil where they will dig in and mature.
Information about the fruit fly can be found at: Maui Master Gardener Program (hawaii.edu)
Maui Master Gardeners has a fruit fly suppression program. Information about the suppression program and a pdf booklet can be found on the Maui Master Gardeners website at: mauimastergardeners.org.
The oriental flower beetle is a hefty beetle with a hard shell that has a bronzy metallic sheen and white markings. The adult beetle is less than two inches long and is an excellent flyer. The beetles eat many types of overripe or damaged fruit including papaya, mango, banana, and coconut.
The adult female beetle lives approximately 135 days and lays close to 83 eggs on average in her life span. The eggs are laid in soil and hatch into C-shaped white grubs. The grubs remain in the soil existing on soil debris and compost until they mature and emerge from the ground.
Information about the oriental flower beetle can be found at: idtools.org/scarab/index.cfm?packageID=2201&entityID=10477
Oriental flower beetles are daytime beetles and like sunny, warm weather. In Hawaii they thrive year-round. They became established on Oahu in the early 2000s and reached Maui in 2010. They are considered an invasive pest and it is helpful to report sightings to the Statewide PEST Hotline by phone at 1-808-643-PEST (7378) or online at: 643PEST.org