May beetles flying around light, and Pyrgota fly ovipositing in a May beetle.

The Pyrgota flies are not the only enemies of May beetles. Several larvaevorid, or tachinid, flies also harass them. But while the Pyrgota flies attack boldly and thrust their eggs into the bodies of the beetles, the larvaevorids attack stealthily. Surreptitiously they fasten their eggs to the bodies of the beetles while their backs are turned.

ANYONE WHO RAISES cabbages or other cruciferous vegetables is sure to become acquainted with the cabbage maggot. We set out young plants in the spring and expect them to grow vigorously, but they wilt and collapse instead. When we pull one up we find the roots and lower stem a flabby bundle of macerated and rotting tissue. Cabbage maggots are tunneling through this nauseous mess.

If we dig in the soil around the infested roots, we are apt to find tiny rove beetles, Aleochara bimaculata. Rove beetles, the main enemy of the cabbage maggot, are less than one-quarter inch long and have slender, shining black bodies and brown legs. When the little beetles run (they never seem to walk but are always in a hurry), they twist their flexible abdomens from side to side or up over their backs. They shun the light, and when we uncover them in the soil they quickly bury themselves again.

In the soil these interesting little creatures construct a series of interconnecting tunnels between tiny subterranean chambers. In this cozy labyrinth the beetles carry on their affairs. Usually several live together in a way that suggests a social life.

The adult beetles feed on cabbage maggots or on other fly maggots in the soil. They are ruthless predators and will attack and eat maggots much larger than themselves. They hunt singly or in small groups through the soil, and when they find a maggot they attack it, tear open its sides, and feed upon it.

The female Aleochara beetle, after mating, lays her eggs in places where the cabbage maggots occur. With that she evidently considers that her duty toward her offspring has been done; she leaves the young larvae to shift for themselves.

The larvae hatch about 10 days after the eggs are laid. They have brown and horny bodies, well-developed heads and mouth parts, and sense receptors and legs much like those of most rove beetle larvae. The minute larvae begin hunting through the soil for the pupae of the cabbage maggot. The pupae are enclosed in puparia formed from the tough and hardened skin of the last larval stage. Even that almost impervious covering is not strong enough to keep the Aleochara larvae out.

Aleochara attacking a cabbage maggot.

When it locates a cabbage maggot puparium, the Aleochara larva sets to work to gnaw a hole in it. It is slow work, but the larva can pierce the barrier after several hours of effort. It then crawls inside and seals the entrance hole behind it. Inside, the larva crawls over the slumbering cabbage maggot pupa until it reaches a spot on the back just at the base-of the head. There it settles down to feed, piercing the skin of the pupa and lapping up the semiliquid contents.

Within 3 or 4 days the Aleochara, is ready to molt. Its skin splits, and the second-stage larva emerges. That larva is different in structure from the active first-stage larva. Its body covering is soft and white, and the sense receptors, legs, and mouth parts have become rudimentary. The larva continues to feed by piercing the skin of the still-living pupa of the cabbage maggot and it grows rapidly. Within another week it has outgrown its second-stage skin and has molted again. It is now full-grown and nearly as large as the cabbage maggot pupa was at the start, while the latter has been reduced to an empty, shriveled skin. The Aleochara rests for a few days and then pupates. Two weeks later the mature adult is ready to emerge.

The adult beetle chews a hole in the wall of the still-tough puparium and comes out. Now it will find a mate, take up the work of enlarging and maintaining the ancestral galleries and chambers, and continue the decimation of the cabbage maggots. In a season as many as 80 percent of the cabbage maggots in a field may fall victim to the aggressive beetles.

BARNARD D. BURKS is an entomologist in the division of insect identification, Bureau of Entomology and Plant Quarantine. Born in New Mexico, he received his doctor's degree in entomology from the University of Illinois. He was a stag member of the Faunistic Survey Section of the Illinois Natural History Survey from 1937 to 1949, although 4 of those years he spent in military service.

Alfalfa caterpillar and butterfly.