7 '*»i5 



Cooperative Extension Service, University of 

 Illinois College of Agriculture in Cooperation With 

 the Illinois Natural History Survey and U.S.D.A. 



FOR IMMEDIATE RELEASE August 12, 1966 



INSECT SURVEY BULLETIN NO. IT 



This seventeenth weekly bulletin on the general insect situation in Illinois 

 (fruit insects excepted), prepared by entomologists of the University of Illinois 

 College of Agriculture, Illinois Natural History Survey and cooperating agencies, 

 reports general trends in insect activity and suggests abbreviated control measures. 

 Each individual should check his own fields to determine local conditions. 



Present Farm Insect Problems 



Corn leaf aphids are still a major concern in many areas. In the area 

 south of Highway 6, peak activity is generally over, most of the damage has been done 

 and populations are rapidly declining. In the area north of Route 6, populations 

 have just reached their peak and damage will continue for another week. Corn that 

 suffered from drought also showed the greatest damage from aphids, although popula- 

 tions were no greater than those in areas with sufficient moisture. 



Aphids are rapidly decreasing or have completely disappeared in early- 

 maturing fields in which all silks have dried and the kernels are developing. In 

 fields in full silk, aphids have reached a peak and are already disappearing from some 

 plants. However, the aphid populations, particularly in northern Illinois, may still 

 increase in late fields that are just shooting tassel and have only a few silks show- 

 ing. 



Certain fields are the exception to the rule. In these fields, the aphids 

 are not disappearing but are dropping down from the tassels and colonizing on the 

 ears and lower leaves. Damage may continue in these fields. 



Lady beetles, green syrphid fly maggots, aphid liens and parasitic wasps 

 all feed on aphids, but they have been present only in small numb^s. They are now 

 increasing and are helping to reduce aphids in some fields. This low pr .cHtor pop- 

 ulation may be the reason for the corn leaf aphid buildup, and there is a reason for 

 these low numbers of predators. Ordinarily moderate popul& ..i<r.is of pea aphids are 

 present in alfalfa fields in spring and early summer. This large food supply enables 

 lady beetles and other predators to build up in large numbers. Then in midsummer, 

 when the pea aphid populations decrease, these predators migrate in swarms to corn- 

 fields in search of food. This year the pea aphid population in alfalfa was the low- 

 est of any year in the past decade. Without pea aphids to eat, the predators \:ere 

 unable to increase. They are just now beginning to find enough food to multiply. 



To control aphids in heavily infested fields, apply 1 l/k pounds of mala- 

 thion or 1 pound of diazinon per acre. At this rate, allow 10 days between applica- 

 tion and harvest when applying malathion. Diazinon sprays can be applied until the 

 day of harvest. 



Corn borer moth emergence and egg laying are progressing in northern Illi- 

 nois. Moths will continue to emerge and lay eggs for at least three weeks. 



Although moths will deposit eggs on all corn, they concentrate their egg 

 laying in fields in the late whorl to early silk stage. To decide whether to apply 

 an insecticide, count the egg masses on several plants in several locations in the 



