Mango flowers, overripe fruit are favorites of pesky beetle

Question: We live in Hawaii Kai and have seen an increase in bumblebee-size beetles. They’re not the coconut rhinoceros beetle. A number of them have been swarming around our mango tree flowers. Are they good or bad and how do we control them?

Answer: You’re being plagued by the Oriental flower beetle, or Protaetia orientalis, which isn’t as destructive as the coconut rhinoceros beetle, but not something you want hanging around your yard, either.

Oriental flower beetles sometime are mistaken for the coconut rhinoceros beetle, which is an object of intense federal and state monitoring, but are one-third its size, with golden speckling on its dorsal side, said Bernarr Kumashiro, insect taxonomist with the state Department of Agriculture.

The department won’t be conducting any control or eradication program against the Oriental flower beetle, which has been in Hawaii for more than a dozen years and is widespread throughout the state, said Neil Reimer, administrator of the Plant Industry Division.

"Eradication is not an option because this would require the treatment or removal of grubs from all breeding sites," he said. "The beetle breeds in decaying plant material and mulch, which is pervasive."

The adult beetle attacks overripe fruit but will not attack ripening fruit, Reimer said. So one option is to pick fruit when it is half ripe, he said.

As you’ve noticed, Oriental flower beetles also go

after fruit blossoms, especially mango blossoms, Kumashiro said.

The oriental flower beetles were first found at Hickam Air Force Base’s Mamala Golf Course in 2002, but only in recent years has the population steadily increased to become a widespread problem.

"Interestingly, CRB also was first discovered at the same golf course in 2012," Kumashiro said. "It is very difficult to trace back where any insect came from, but we suspect that OFB may have come from Guam. For the first 10 years, OFB was reported infrequently and was considered innocuous, but from 2012 the reports began increasing substantially."

Kumashiro said there has been a surge in calls about the beetles, with five to 10 calls a day to the Agriculture Department’s Plant Quarantine Pest Hotline.

About 40 to 50 calls a day are made to the coconut rhinoceros beetle team. But the majority of those calls, about 30 daily, are determined to be about Oriental flower beetles, Kumashiro said. With the mango flowering season in full bloom, that’s understandable.

"Adult beetles fly during the day, and can sometimes be seen swarming around flowering trees and feeding on nectar and pollen," he said. "They have a preference for mango blossoms. Because of its large size and strength, they can easily damage the delicate flower parts."

Controlling PESTS

If adult beetles are causing a problem on trees, Kumashiro said a strong water spray from the garden hose can be used to deter them.

The beetles have been reported attacking and consuming overripe soft fruits, such as mango, papaya, banana and tomato.

"Dozens of beetles sometimes congregate on a single fruit, creating an awesome but frightful sight," Kumashiro said. "The simple solution is to pick the fruits when they are half ripened and allowing them to ripen indoors."

Also, get rid of any ripe fruits on the ground.

Meanwhile, Oriental flower beetle larvae breed in mulch piles, much like the coconut rhinoceros beetle, Kumashiro said.

"In some cases, eliminating the breeding sites within the property will reduce the adult population, but the adults may still fly in from blocks away," he said. "If you are an organic farmer, you may try removing the larvae from the mulch with a screen sifter."

Reporting Pests

Call the state pest hotline (643-7378) to report any pests, or the coconut rhinoceros beetle line (832-0585) to specifically report that beetle.

Write to “Kokua Line” at Honolulu Star-Advertiser, 7 Waterfront Plaza, Suite 210, 500 Ala Moana Blvd., Honolulu 96813; call 529-4773; fax 529-4750; or email kokualine@staradvertiser.com.