L2LS 



COLLEGE OF 

 AGRICULTURE 

 UNIVERSITY OF 

 ILLINOIS AT 

 URBANA-CHAMPAIGN 

 AND NATURAL 

 HISTORY SURVEY 

 URBANA. ILLINOIS 



NSECT, WEED & PLANT DISEASE SURVEY BULLETIN 



rATE/COUNTY/LOCAL GROUPS/US. DEPARTMENT OF AGRICULTURE COOPERATING 



FOR IMMEDIATE RELEASE 



No. 17, July 13, 1973 



This series of weekly bulletins provides a general look at the insect, weed, and 

 plant disease situation (fruit and commercial vegetables excepted) , along with 

 suggested, abbreviated, control measures. Each individual should check his own 

 fields to determine local conditions. THE- 



INSECTS 



oitv DF III ' 



CORN INSECTS 



Corn leaf aphids are present in almost all corn fields , but numerous natural enemies 

 are present. One species, the insidious flower bug (which looks like a miniature 

 chinch bug) is very abundant. It inserts its siphon-like beak into other insects and 

 siphons -out the body fluids. This species may help hold down the aphid populations. 



Swollen brown aphids, each with a tiny hole in the back, have been parasitized by a 

 wasp. A large number of such aphids indicates lots of natural control help. Brown, 

 flattened cottony- looking aphid bodies are aphids that have died from a fungus dis- 

 ease. High humidity favors the spread of this disease. It can actually annihilate an 

 aphid infestation. We did not see wasp parasites or aphids killed by fungus this week. 



Each aphid killed now by a natural enemy prevents the birth of a thousand aphids dur- 

 ing the next two weeks. But ordinarily, natural enemies are unable to contain a pest 

 population when conditions are favorable for a high reproductive rate of the pest. 



Despite some favorable things, we must be pessimistic about corn leaf aphids during 

 the next three to four weeks. Damage from them is accentuated during stress periods of 

 growth from the pretassel to dry silk stages. The same aphid population in a period of 

 drought can be far more damaging than during a time of plentiful moisture. Hopefully, 

 soil moisture will be sufficient to help corn plants through the stress of growth dur- 

 ing the next four weeks. 



Aphid reproduction and survival is highest when corn development is from pretassel to 

 dry silk- -most corn fields will be in that stage of growth during the next few weeks. 

 On the favorable side is the fact that we do not, to our knowledge, have a large acre- 

 age of susceptible hybrids as we did in the late 1960 's when damage was severe. 



This week, we found corn leaf aphids in all of the fields examined. However, in this 

 random examination of over a hundred fields, we saw only one we thought would develop 

 into a problem field. But we did find aphid reproduction occurring in almost every 

 field. Fields averaged from 2 or 3 aphids per plant on 10 to 20 percent of the plants 

 to the one field, which averaged over 100 per plant. 



Aphids give birth to living young. They do not lay eggs. Every aphid you see in a 

 corn field is a female- -there are no males. A mature aphid gives birth to 2 to 7 aphids 



