Insect identification > Hemiptera > Chinch bugs

Chinch bugs


The chinch bug (Blissus leucopterus Say). - This little bug, less than a quarter of an inch long, feeds on all the grasses and cereal crops. It is apparently a native of tropical America which has migrated northward, up the Atlantic Coast, the Mississippi Valley and the Pacific Coast, and is now found everywhere south of the St. Lawrence River and the Great Lakes and also in southern Ontario, Minnesota, Manitoba, the Dakotas and along the eastern slope of the Rocky Mountains to Texas.

It has also been found in Arizona, California and Washington. It is not a serious pest, usually, in the Northeastern states and many of the others, but in the Mississippi Valley it often destroys crops valued at millions of dollars in one season.

The adult bug is a tiny insect seemingly incapable of causing so much injury, but its enormous numbers make up for its small size. Its body is black or dark gray, with white and therefore conspicuous wings, each having a single black spot.

There are two forms of adult, however: one with long full-sized wings, the other with short wings only partially covering the top of the abdomen. The former occurs in the Mississippi Valley while the latter is met with, together with the long­winged form, in the Atlantic states and to some extent inland from there along the more southern of the Great Lakes to Illinois.

The long-winged form passes the winter as the adult in grass tufts, under fallen leaves or in other places giving it protection. Corn shocks left out over winter often harbor enormous numbers. In spring the bugs leave their winter quarters and fly to the grain fields. Here they lay their eggs, several hundred in number, on the ground at the base of the plants or on the roots just below the surface, this process lasting about a month.

The average length of the egg stage is about 2 weeks and the young which hatch suck the sap from the plants for about 40 days before becoming adult. The nymphs are yellow with an orange tinge about in the middle of the abdomen. This soon spreads over the greater part of the body.

In later stages the red becomes vermilion, with a pale band across the front of the abdomen, the head and prothorax dusky, and before becoming adult the red becomes quite dark.

Development, at least for the individuals coming from the later eggs, is not complete before harvesting time, and to finish their growth they are obliged to migrate and find more food. They accordingly march in armies, often travelling some little distance on foot, and many which have already become adults, able to fly, march with them. In new feeding grounds development is completed and the eggs for a second generation are laid. This generation appears to feed more particularly on corn, kafir corn, millet and other similar crops, and its members become adult before winter and go into hiding until the following spring.

With the short-winged form, hibernation at a distance from its food plant is impossible because of its inability to fly. This form therefore winters in grassland and begins its work there in the spring. It is a question whether there is more than one generation a year for this form. Migrations, when they occur, are, of course, on foot, and corn is no more liable to be attacked than timothy or any other grass crop.

The chinch bug is particularly affected by weather conditions, dry weather being favorable, and wet seasons unfavorable. Dry weather appears to induce migration, and a succession of several dry years favors a large increase in their numbers and consequently of the injury they cause.

Rains during the hatching periods of the eggs are very destructive to the insect, and the suppression of a chinch-bug attack, anticipated because of the great abundance of the wintering bugs, by heavy rains at the right time in the spring is one reason why these pests are not even more serious than is the case.

A fungus (Sporotrichum globuliferum Speg.), generally called the "chinch bug fungus," frequently attacks this insect, particularly during periods of wet, cool, cloudy weather, and then kills enormous numbers of them. In dry seasons it seems to have little effect, and attempts to control the chinch bug by placing individuals inoculated with the fungus in infested fields, while successful from the experimental stand­point, have on the whole hardly produced the results hoped for. It is most valuable in seasons which are dry during the egg-hatching period but wet thereafter.

In seasons, then, when rains occur during the egg-hatching periods of the bugs, these and the fungus present will usually prevent serious outbreaks. In dry seasons, and particularly where there are several in succession, artificial methods of control must be resorted to.