Ask A Master Gardener – Two Pesky Insects

Much has been written about emerald ash borers and Asian lady beetles. Most gardeners are well aware of the damage these invasive insects can cause and how to either treat them or find help fighting them.  However, there are two more problem insects on the horizon about which gardeners should become educated and be vigilant in scouting.

The brown marmorated stink bug (BMSB), “Halyomorpha halys”, is an invasive (non-native) pest originally from Asia. It was first found in Pennsylvania in 1998, but has steadily spread across the United States. It was first detected in Wisconsin in 2010 and by 2016 populations had caused damage to a wide range of fruit and vegetable crops, specifically apples, sweet corn, tomatoes, and pumpkins, as well as ornamental plants.

There are native stink bugs, some of them are beneficial, and they have natural predators. Therefore, they do not reach the destructive populations of the BMSB. Hence, it is important to correctly identify the BMSB before taking action.  Size, distinctive bands on the abdomen, and smooth shoulders are all distinguishing features.  The website has clear photos to help differentiate between the species.

BMSB adults look for warm places to overwinter. Inside houses, barns, and in secluded garden areas are a prime home to a cold BMSB. Eggs are laid in the spring and a single female can lay nearly 500 eggs in her lifetime. They feed, as do all true bugs, by piercing the fruit and sucking out the juices.  Not only does this damage the fruit, but it leaves it susceptible to disease, causing further damage.

BMSB can be removed by hand picking or vacuuming when populations are low. If numbers escalate, chemical control may become necessary.  By all means, keep them out of the house.  Install weather stripping around doors, caulk cracks, and put screens over chimney or other entry points.  Under no circumstances should a person crush a BMSB.  They come by their name legitimately since the odor they omit is offensive and will linger for days.

A second and increasingly problematic insect is the spotted wing drosophila (SWD), “Drosophila suzukii”. This invasive insect also hails from Asia.  It was first discovered in the continental United Stated in California in 2008.  It spread rapidly and by 2010, was in many Wisconsin counties.

SWD are a type of vinegar fly, commonly referred to as “fruit flies”. However, the biggest difference is that fruit flies feed on dead or damaged fruit.  The female SWD has a serrated ovipositor, or a sharp keister, that allows her to cut into healthy fruit and lay her eggs. This pest poses a hazard to most berries and tree fruits; however, they seem to have a special affinity to raspberries.  No one likes to pick a bucket of raspberries and find little white worms crawling to the surface when they try to eat them.

Traps made with a 32-ounce container, dish soap, water and yeast are particularly effective with SWD. (See for further information.) They are attracted to damaged fruit, so keep the raspberry patch meticulously clean, tossing out each and every damaged fruit.  Harvest frequently to keep fruit from overripening.

With careful scouting, monitoring, and alertness much can be done to keep these two invasive insects at bay.

Carol Shirk

Certified Master Gardener

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