Know Your Friends

Spined Soldier Bug

The spined soldier bug, Podisus maculiventris (Say), is a native North American insect found from Quebec to Florida, from New England to the Pacific. It is a "generalist" and can feed on over 50 different types of prey, primarily the larvae of beetles and moths. While more common in southern areas of the U.S., this predator can be readily found in many crop and non-crop environments in the Midwest. The spined soldier bug is one of the generalist predators that help keep pest populations low in crops such as alfalfa, soybeans and fruit crops. This bug has "piecing-sucking" mouthparts which it uses to impale prey and suck out their internal juices. Occasionally, the bugs enjoy a little salad with their meat, by sucking on plants to obtain moisture. The plants aren't harmed and the bugs don't transmit disease. In a way, by providing moisture to predators, the plants help to keep the predator around until pests appear!

Adult spined soldier bugs are brownish, about the size of your fingernail and have a prominent spine on each "shoulder." (This is not the origin of the name spined soldier bug . . . the "spined" refers to spines on the legs!) They overwinter as adults, hiding in leaf litter in woods around fields, and begin emerging around mid-April in Indiana. Females can lay up to 500 eggs and live up to 125 days. Males are slightly smaller than females and live up to 180 days. Females begin depositing eggs 4-7 days after emerging. The number of eggs a female lays depends on how well she is fed the more she eats the more eggs she lays and on the type of prey she eats (Colorado potato beetles are particularly "bad" prey; Mexican bean beetles are "ok"). Survival, development, body weight and longevity also depend on the type of prey and the frequency of feeding. Females in the field eat about 1 prey every 2 days, which is a lot less than they can eat when food is readily available. Females fed too much often die earlier than those fed less perhaps a health lesson to us all!

The eggs are deposited in masses of 15-70, and range in color from cream-colored to black. Eggs hatch in 4-7 days, depending on temperature. The brick red first instar spined soldier bugs are not predaceous (indeed they eat nothing at all!), whereas the remaining 4 instars (immature stages), are predaceous. Development from newly hatched to adult takes 25-30 days. There are 1-3 generations per year.

Probably because spined soldier bugs are large and easy to rear in the lab, they have been the object of much study and a number of attempts for biological control. The largest, most sustained attempt was releases in a biological control program (see MBCN No. 1, Vol. 4) against Colorado potato beetle in Eastern Europe and the former Soviet Union. The attentive reader will note that since both predators and prey were introduced into Eastern Europe (both are native to North America), the initial effort was an attempt at "classical biological control" (see MBCN No. 1, Vol. 3). This underscores an important point: many augmentative programs have their roots in classical efforts! Millions of spined soldier bugs were reared and released, with very promising results. However, with the collapse of communism, the spined soldier bug's fortunes declined and the program was discontinued.

In the U.S., the spined soldier bug has shown promise in augmentative biological control in both potatoes (Colorado potato beetle) and soybeans (Mexican bean beetle). However, the costs of these efforts is still not competitive with chemical applications, and so more research needs to be done, particularly on rearing methods and release strategies. At this point in time, spined soldier bugs are not available for sale in the U.S.

- Bob O'Neil, Purdue University

Drawings by Michele Schwengel
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