Natural Control
Orius insidiosus (Say)
Insidious plant bug
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The insidious pirate bug, Orius insidiosus (Say) belong to the insect order, Hemiptera, and the family, Anthocoridae, which has about 70 species, all with the common name, minute pirate bugs (MPB). Orius insidiosus is the most common species in the eastern and central United States. Orius tristicolor (White) occupies a similar ecological niche in the western states.
Minute pirate bugs are small, with flattened bodies, ranging from 2-5 mm in length. The head is somewhat pointed, with a three-segmented labium, which forms a sheath around the sucking mouthparts. Both large compound eyes and three small ocelli or simple eyes are present. On close examination a thickened part of the forewing, called the cuneus, can be seen. As in most Hemiptera, the forewing has a thickened, leathery basal part, and a thin, membranous part at the tip. In O. insidiosus, the fore part of the forewing is yellow, and the remainder of the body is black.
Immature MPB are yellow to red in the first two instars, but turn dark brown as the wing pads develop in later instars. In the light yellow immatures, a red glandular area is present on the top of the abdomen. Immature MPB are about the same size, 0.5-2.0 mm in length, and color as many of the thrips upon which they prey.
Host Range
MPB are found in the blooms or on young foliage of many host plants. The feed voraciously on thrips, but may prey on other insects.
Economic Importance and Management Specifics
MPB can quickly reduce a thrips population to below damaging levels. For this reason, careful scouting is required to determine their presence. Except in crops where tomato spotted wilt virus is a factor, this predator may be the exclusive thrips control needed by a grower. Scouts and pest managers should become familiar with the seasonal abundance and migration cycles of locally common thrips species in weeds and local crops. This familiarity can help in anticipating the often simultaneous migrations of thrips and MPB.
In south Florida, for example, the Florida flower thrips usually migrates into fall pepper plantings from surrounding native vegetation. MPB can be found in pepper fields shortly thereafter. Yet in February and March, when thrips immigrate from citrus groves, seldom are they accompanied by significant numbers of MPB. The reason for this difference is not clear, but probably due to the unsuitability of citrus as an MPB host.
MPB have a winter diapause, triggered by either daylength under ten to twelve hours or low temperatures. During this period of low activity, these predators can be found in association with thrips, but their feeding activity and reproduction are greatly reduced compared to the fall season. While the thrips influx into fall crops often requires no insecticide applications for control, the spring migration often does. These two scenarios often occur on the same farm. This stresses the importance of a detailed, ecologically oriented scouting program.
The choice of insecticides selected to manage other insect in vegetable crops is critcal due to the potential impact on the MPB population. Biological insecticides, such as Bacillus thuringiensis are less harmful to MPB than conventional insecticides. Soaps and crop oils have a measurable, but are usually less harmful than pyrethroid, organophosphate or carbamate insecticides. A sizeable population of MPB can recover from single applications of more toxic pesticides, provided the residual activity is short. Shorter residual pesticides such as acephate or methomyl, when used at lower rates to control other insects have not eleiminated MPB, but have allowed sufficient numbers to remain in the field to keep thrips population under control.
The choice of insecticides in any management program will vary according to the growing region and the crop. Growers interested in preserving these highly beneficial insects should seek the advice of a qualified agricultural professional before treating their fields.
In some situations mass releasing MPB or other general predators, such as the big-eyed bug, Geocoris punctipes (Say), may be a practical way to augment their populations. Commercially produced befeicial insects are available from an increasing number of insectaries nationwide (Hunter 1994). Updated information on suppliers of beneficial insects is availabe on the World Wide Web at:
http://www.cdpr.ca.gov/docs/pestmgt/ipminov/bensuppl.htm
Suppliers may be limited seasonally, and the insectary should be contacted well in advance of the planned release date. Local gardening clubs, Cooperative Extension Service agents and universities should be able to provide information on reliable insectaries.
The quality of purchased beneficial insects is a critical issue. Some state agencies, such as the Florida Department of Agriculture and Consumer Services' Division of Plant Industry, will examine sample of beneficial insects from the commercial vemdors to verify their identity and viability. A permit to ship live insects across state lines may be required in some areas.
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