Elementary lessons on insects (1928) Elementary lessons on insects elementarylesson00need Year: 1928 CONTROL MEASURES 149 keep the plantings freed from insect pests. Hogs, if allowed tor oot, will clear a field of white grubs. Hop growers protect the skunk because it so diligently searches out the hop borers for food. A big ground beetle has been successfully imported from Europe to help keep down the numbers of the gipsy moth in New England. The importation of a ladybird beetle into California once saved the citrus orchards from the ravages of the cottony cushion scale. All these are predato
Elementary lessons on insects (1928) Elementary lessons on insects elementarylesson00need Year: 1928 CONTROL MEASURES 149 keep the plantings freed from insect pests. Hogs, if allowed tor oot, will clear a field of white grubs. Hop growers protect the skunk because it so diligently searches out the hop borers for food. A big ground beetle has been successfully imported from Europe to help keep down the numbers of the gipsy moth in New England. The importation of a ladybird beetle into California once saved the citrus orchards from the ravages of the cottony cushion scale. All these are predatory enemies. There are parasitic ones as well; and these very small ones are even more important in re- ~^$«&&i ducing the numbers of injurious species. How to best utilize the aid of these para- sites is one of the live subjects of ento- mological investiga- tion at the present time. 10. Trap crops and miscellaneous.—Trap crops are sometimes effective. For ex- ample, early kale is sometimes grown in the South to attract all the early harle- Fig. 57.—The work of Hymenopterus parasites. At <* t is shown a dead caterpillar, killed by parasites, some of whictrhave spun their cocoons beside it, others, on the grass blade above. At b is shown an easy way to get the adult parasites: put the cocoons in a vial and stop its mouth with a plug of cotton, and wait for them to appear.
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