The barley jointworm, Harmolita hordei (Harr.), was first discovered at a point in the northeastern part of Prince Edward Island in 1946. It spread quite rapidly along the northern coastline of the province and more slowly southward, and today infestations may be found in most areas of the province. Inland movement of the pest did not start until about 1955 and since that time infestations have generally been lighter than they were previously.

H. hordei overwinters as mature larvae in galls in barley stubble left in fields after the grain is harvested. Adults emerge the following year during late June and early July and oviposit in the stems of young barley plants, usually when the plants are six to eight inches high. Eggs are almost always laid just above the lower nodes or joints, either on the main or on tillering stems. The adults live for four to eight days. The larvae develop inside the stems and the plant tissue around them develops into hard, woody galls. The larvae mature in three to four weeks and, thereafter, remain dormant inside the galls in the stems until the following year. Infested barley plants are stunted and heads may fail to develop or, if formed, contain small, shrivelled kernels. In severely infested fields, the grain crop is considered a complete loss.

There are six speoies of parasites known to attack H. hordei in Prince Edward Island, and all of them are chalcids that closely resemble the pest. Parasite eggs are deposited in the stem with the host and the larvae attack and destroy H. hordei larvae and then complete their development inside the galls. In addition to biological control by natural parasites, the other major natural control agent is considered to be weather, combinations of moisture, humidity, and temperature. However, further investigations are necessary to establish the influence of these different factors.