REPORT OF THE STATE ENTOMOLOGIST I9O9 85 



perature and the multiplicaiion of plant lice. The past summer 

 was remarkably cool and backward, a marked change for the 

 better occurring June 21. That the earlier cool weather was 

 favorable to the plant lice, was evidenced by the hosts occurring 

 upon the leaves of many trees. The reason is probably found in 

 the fact that the unusually low temperature prevented the nor- 

 mal activity of such natural enemies as ladybeetles, flower flies 

 and minute 4-winged parasites. Prior to the appearance of 

 warm weather numerous lots of plant lice, showing no evidence 

 of having been materially injured by natural enemies of one kind 

 or another, were received. Shortly after the rise in temperature 

 a very different condition of affairs obtained. Leaves injured 

 by plant lice continued to be received, but in almost every case 

 3. few natural enemies had begun to reduce the numbers of the 

 pests, or especially toward the end of the outbreak, most had 

 heen destroyed and the leaves only bore evidence of earlier 

 injury. Recent observations on the spring grain aphis in the 

 Southern and Middle States have shown a similar correlation 

 between temperature and the development of plant lice and their 

 enemies. 



The obvious lesson to be drawn from the above is that plant 

 lice outbreaks may be expected when the late spring weather is 

 unusually cool and backward, unless it is accompanied by pelt- 

 ing rains which are undoubtedly of considerable service in 

 destroying exposed aphids. The advisability of adopting direct 

 repressive measures in specific instances, must depend in large 

 measure upon the probability of warmer weather developing 

 soon enough so that natural enemies may check the aphids 

 before material injury is caused. 



Ants and aphids 

 There is a somewhat intimate relation existing between ants 

 and aphids. The former appreciate the sweet excretions of the 

 latter and not infrequently protect and even construct shelters 

 for various species of plant lice. The popular characterization 

 of aphids as the milch cows of ants, expresses fairly correctly 

 the relationship which may exist between such divergent forms, 

 though possibly it implies too much interdependence on the 

 part of both. Ants can subsist without the secretions of plant 

 lice ; and conversely, protection by ants is not necessary to the 

 ^existence of aphids. There are well recognized cases where ants 



