Sri Lanka Weevil

On a recent visit to Florida’s Manatee county, this poor Crepe myrtle was brought to my attention.

A branch from a crepe myrtle eaten up by the weevil

The owner of the plant said that white insects were found on it. Sure enough in a few seconds of searching, a white weevil was found. Here you can see him pinned down for a really awful picture.

The perpetrator pinned down on the countertop by a shish-kebab skewer. They are not much for flying away.

After a few minutes search on the internet, I think this insect is probably the “Infamous” (heh-heh) white weevil from Sri Lanka. As one of the many invasive insects coming into the USA each year, this one is without natural predators or diseases and has been increasing in Florida and other places. This insect has a very wide range of plant hosts so it will probably be successful all over the place. It seems to eat everything and the kitchen sink. Unfortunately, it seems to eat citrus plants which will cause Florida some problems. Obviously, it likes Crepe Myrtle too.

I do not know anything about this insect in particular since it is a relatively new import, but I know about a cousin of it, the Black Vine Weevil. I can tell you about its life cycle and how nurserymen have been handling it.

The Black Vine Weevil is primarily a root feeding insect. Most of their lives they exist as immature grubs that eat roots of susceptible plants. They overwinter in the soil, moving downwards as the soil temperature drops in the fall. After winter, they warm up and rise shallower and shallower in the soil until they are just under the surface by spring. Here they pupate and turn into adult beetles. If you are a curious human, your best bet is to find them in the shallow soil or leaves on top of the ground. The Black Vine Weevil is nocturnal in its adult form.

The adults emerge when the weather turns warm and they begin to feed on the foliage. All weevils have a snout with a little mouth at the tip. It is characteristic of the Family. The little mouth chews a smile shaped bite out of the leaves of its host. You can pretty easily look at a weevil-eaten leaf and say it was done by a member of the Weevil family. The only other insect making even close to this feeding pattern is the grasshopper and their feeding is quite rough-looking in comparison. Anyway, the feeding damage occurs at night and is sometimes quite heavy. Our little friend on the Crepe-myrtyle make a big mess of the leaves. In the day, weevils of the Black Vine type sleep down in the shade under the plant. That is where I found the Sri-Lankan one too, so it may be nocturnal also.

Something very strange occurs with the Black Vine weevil. There are no males. Only females exist. Females spontaneously create parthenogenic eggs and lay them in the soil under host plants. I do not know why they never have any males, but there it is, ladies. A species of complete feminists for you. I am not sure how common this is in weevils but there are a few other insects that do this durung certain times of the year, like aphids. I do not know of any other completely female species, but, like I always say, I don’t know much.

As far as control, they Black Vine Weevil can be treated by dosing the soil around the affected plant with a water can full of pesticide. This is best done in early summer as you notice the first little bit of adult notching on the new leaf growth. Then spray the foliage once per month during the summer. The first drenching in the soil will kill active grubs that are root-feeding. Then the adults eating the leaves get knocked off from their lunch. If you are into this sort of thing, you can easily flashlight your way around the garden at night and hand-pick hundreds of them. They are slow and non-flying. Hand collection is not a good control measure because they hide in the shadows and are pretty sneaky. Weevils also walk into homes pretty frequently on cold nights. They come in and get lost and never get out. If you have weevils in your foundation plants, you will probably find a few lost in your garage!