Gardening and Living in Grand Style
The bumble flower beetle, really — no kidding...
by Michael Johnson
Utah State University Extension Agent, Grand County
Aug 25, 2016 | 2998 views | 0 0 comments | 152 152 recommendations | email to a friend | print
Gardening column: Bumble flower beetle and root weevil
The bumble flower beetle is rarely seen, but active in the area.
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Temperatures continue to moderate as our gardening is in full swing. As expected, this doesn’t stop reports of insects. In the insect realm, gardeners know that insect populations are large some years and in other years they’re rarely to be seen.

This year we’ve seen an increased incidence of one not often heard from — the bumble flower beetle — and a regular that has upped its game — the root weevil. So, another typical summer, right?

Bumble flower beetle

The bumble flower beetle is an insect I very rarely hear about. However, it has popped up in the last couple of weeks more than ever before. This beetle is a member of the Scarabaeidae (or scarab) beetle family. Bumble flower beetle, really, you ask? Well, it’s not because there’s a bumble flower out there you haven’t heard about. Rather, they get the name due to emitting a loud buzzing sound that people associate with a bumblebee.

This year they’ve been seen on poplars or cottonwoods that are emitting fluids most think is sap. Initially, people were concerned the beetles were boring into the trees and causing the fluid flow. As it turns out, the fluid was caused, most likely in all cases, by slime flux, a bacterial disease. The beetles and larvae feed on fermenting material — hence the slime flux — or decomposing organic material. The beetles are about one-half-inch long and one-quarter-inch wide. As with many beetles the wings covering their backs appear to be the outer shell casing. Their color varies from a light tan to dark brown or black with many small black spots, and those we’ve seen so far have been dark colored. They become active once it starts warming up in the spring and lay eggs that hatch into grubs, as is common in this family of insects. Since the adults feed on decomposing plant material, most of us would likely see them feeding on damaged fruit. But again, they aren’t the cause of the damage, just taking advantage of it. Usually no control is warranted other than removing the damaged fruit or other organic material.

Root weevil

An insect having a resurgence lately is the root weevil. Calls come in asking about something eating plant leaves and leaving semi-circular notches along the sides of the leaf, a very characteristic mark of root weevils.

In Utah we have the lilac, strawberry and rough strawberry root weevils as well as the black vine weevil. Adults are somewhat round beetles, from one-quarter-inch to one-half-inch in size, with a “snout” where their mouthparts are located. They are active mostly at night. Even when feeding in the evening people don’t see them, as they will drop to the ground and hide.

The larvae are the most problematic life cycle of this insect, being small grubs that feed on the roots of plants. Obviously, the smaller the plant the more concern with this root feeding. However, when the population gets really large you can see them attacking all types of plants, including shrubs beyond the lilac, which they like to feed on, and perennials.

While the best time to manage root weevils is in the spring or early summer the next best time is the fall. Some non-organic controls for adults include pyrethroids such as bifenthrin or cyfluthrin. Organic controls for larvae include azadirachtin (neem) — which you can mix with water and then thoroughly soak the soil around the plant — as well as biological controls using nematodes that target the larvae. These are mixed with water and applied to the soil from early summer to early fall, however, they only work well when the soil stays moist and the nematodes don’t appear to live over the winter.

Thought for the day: “Some primal termite knocked on wood and tasted it, and found it good! And that is why your Cousin May fell through the parlor floor today.” —Ogden Nash.

Previous articles are available at The Times-Independent website, www.moabtimes.com. Have an idea you’d like Mike to consider writing about? Want more information about these topics? Call the Utah State University Extension Grand County office at 435-259-7558 or email Mike Johnson at mike.johnson@usu.edu.


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