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Insect internal structure
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Insect identification > Coleoptera > True Coleoptera > Asparagus beetle
The asparagus beetle (Crioceris asparagi L.). - This insect reached the U.S. from Europe about 1856 and is now present nearly everywhere where asparagus is grown.
The adult beetle is a little less than 0.25 in. long. It is dark blue or bluish black, with a red thorax, and its elytra are dark blue and yellow, the former present as a band along the middle, with two lateral extensions toward the sides into the yellow, while the outer border is reddish. The distribution and amount of the blue and yellow vary considerably according to the locality, the blue often so encroaching on the yellow as to leave only six spots of the latter color.
The insect winters in the beetle stage in any protected place it can find and, as the asparagus plants begin to come up in spring, leaves its winter quarters to feed and lay its eggs. The beetles at this time feed on the stems and when abundant do considerable harm.
The eggs are laid on the stems, singly, attached by one end, are dark brown in color, and hatch in 3 to 8 days according to the temperature. The grubs, often called "slugs," are gray with black heads. They feed from 10 days to 2 weeks, gnawing the stems, and thus aid the beetles in making these unfit for sale. Then they enter the ground and pupate for about a week, which is followed by the emergence of the adults.
The life cycle therefore is from about 4 weeks during hot weather to 6 or 7 weeks in spring or fall. There are at least two generations in the North and probably three or four in the South each year.
The later generations feed on the leafy growth and in the case of young plants may seriously weaken them. Eggs when abundant on the stems cut for market are objectionable, and a black fluid, poured out by the grubs when disturbed, often stains the stems also.
Fortunately, excessive heat appears to kill many of the grubs, and the alternation of severe cold with much warmer periods in winter has a similar effect on hibernating adults.
Several parasites and other enemies also reduce the numbers of this pest.