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Black and Yellow Flies, Hackberry Tree Leaf Problems, and Galls
By John Fulton

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[July 28, 2016]  Black and Yellow Flies - The appearance of the black and yellow flies we have become accustomed to probably means we have had a good year for flowers and also higher than normal aphid populations. .

The yellow and black insects commonly called sweat bees are actually flies. Syrphid flies to be correct. Sweat bees are about a quarter of an inch long, and are usually a metallic green in color When in doubt, count the wings (I know – easier said than done). Bees will have two wings per side, while flies have one.

Syrphid fly is a generic name given to an entire group of flies. There are some differences in appearance and color, but the yellow and black color is the major one in our area. The other names for syrphid flies are hover flies or flower flies. They tend to hover around your arms and face when you have been perspiring, and land to lap up the sweat. They are also commonly found on flowers, hence the flower fly name, and do a good job of pollinating.

Syrphid flies are actually beneficial insects. They help pollinate, larvae feed on dead organic matter, and the larvae are predators of aphids. They cannot sting, but their mouthparts can usually be felt when lapping up sweat from sensitive areas. You may feel a slight pinch which makes you feel like you’ve been stung or bitten.

Hackberry Tree Leaf Problems

There is a disease of hackberry leaves that appears as blocky yellow spots. The spots often have green tissue surrounding them (but not always), so the disease has earned the name of island chlorosis. In addition to causing the yellowing symptoms, the chlorosis can cause some leaf drop. The disease is mainly a curiosity on established hackberry trees, and causes little damage.

The other item of note on hackberries is the presence of the hackberry leaf gall, which appears as a “thimble shaped” leaf swelling. See the general gall information below.

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 Galls



One group of problems showing up is galls. Galls are swelling of leaves, twigs, or other plant parts. Most are caused by mites or wasps. They damage the plant parts and the plant responds with a gall. In the case of leaves, the swelling is actually leaf tissue. This is something I like to refer to as similar to you getting a mosquito bite. The damage comes in and a swelling occurs. There is no way to get rid of it without tearing a small hole in the leaf. The maple leaf bladder gall will be easily spotted on silver maples in the area shortly, and oak leaves in the red oak group are also showing galls.

Oak trees probably have more galls than any other group of trees. Several samples have also been brought in of the stem types of galls. Fortunately, the oak galls are usually not the type to kill tissue beyond them. However, the galls aren’t the most pleasant things to look at. That is the main thing – they are unsightly.

There is no cure for galls, as they are caused by insects before you see the swellings. The timing would be impossible to try and prevent the insects.

[By JOHN FULTON, COUNTY EXTENSION DIRECTOR SERVING LOGAN, MENARD, AND SANGAMON COUNTIES]

 

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