July 25, 2007
One of the largest insects in Iowa is the dobsonfly (Corydalus spp., Neuroptera: Corydalidae), an aquatic insect from rivers and streams that is frequently found in town. These prehistoric-looking creatures measure two to four inches from the front of the head to the wing tips. They are soft-bodied and brownish-gray with the wings held roof like over the body. The wings have a large number of veins (lines) and are often mottled. The antennae are long and threadlike. A distinguishing characteristic is the mandibles.
Sap beetles are a common nuisance pest in late summer and fall. As the name implies they feed on plant sap, especially fermenting sap from ripe or overripe produce in the garden. They are particularly common on strawberries, raspberries, tomatoes, sweet corn and other garden fruits and vegetables.
Although I've been diagnosing plant problems for a few years, I'm sometimes surprised at the number of plant samples we receive in the Clinic that have no infectious disease or insect problem (about half our samples). The plants have problems, and may have shown symptoms or declined for several years, but the symptoms are not caused by an infectious disease or an insect. Instead, some "abiotic" stress is causing the plant to wilt, turn brown, or decline or, in many cases, a variety of stresses are accumulating to cause serious problems.