40 BULLETIN 746, U. S. DEPARTMENT OF AGRICULTURE. 



larva or a pupa unless it has been injured in some manner. The 

 damage produced by ants in increasing the number of mealybugs, 

 and as sugar-house and household pests, more than offsets any good 

 which may come from their destruction of insects. 



The Egg Parasite, Tkichogramma minutum Riley. 



On account of its economic importance TricJw gramma minutum 

 (fig. 11) deserves more extended consideration. It is almost micro- 

 scopic, and belongs to the large order of Hymenoptera, which in- 

 cludes the bees and wasps. Under the microscope its wings are found 

 to be fringed with delicate hairs and to have lines of these hairs run- 

 ning across their surfaces. 



The adults are about one-fiftieth of an inch long, with a wing ex- 

 panse of a little more than the length of the body. On account of 

 their minute size they are practically invisible in a sugar-cane field, 

 even though they may be present in great numbers. The best way 

 to find them is to search for a cluster of moth-borer eggs which have 

 turned black (indicating parasitism). During the summer, and 

 especially in the fall, an experienced person can sometimes find these 

 clusters in considerable numbers on the leaves both of corn and of 

 sugar cane. If the eggs are put in a small tube and observed for a 

 few days, many light yellow Trichogramma adults may be found to 

 emerge. 



In the fields the females of these parasites search for moth-borer 

 eggs very soon after emergence. Finding a cluster, the female in- 

 serts her own eggs into the borer eggs, and in the course of eight 

 days or longer, depending on the season, a new generation emerges, 

 the parasites having developed from Qgg to adult within the moth 

 eggs. 



The parasites are scarce at the beginning of the season, and in fact 

 eggs destroyed by them were never found earlier than June 18 in 

 Louisiana. As the season progresses they become more and more 

 abundant, until at last they destroy almost every egg cluster of the 

 moth borer. 



If the parasites could be so controlled that they would start their 

 beneficial work earlier in the year, great good would result in lim- 

 iting the ravages of the moth borer. Low temperatures retard the 

 development of insects, and in an experiment to keep them over the 

 winter parasitized eggs were placed in a refrigerator having a uni- 

 form temperature of about 50° F. Some of the parasites emerged 

 even at this temperature, however, and all of them died during the 

 winter. 



Under natural conditions they undoubtedly hibernate in the cane 

 trash left on the fields of the sugar plantations, at least until the 

 trash is burned, when many of them are probably destroyed. This 



