(,33- 2. 



-T- ej Cooperative Extension Service, University of 



-*-^ i ~ I Illinois College of Agriculture in Cooperation with 



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



FOR IMMEDIATE RELEASE August 13, 19&5 



INSECT SURVEY BULLETIN NO. 17 



This is the seventeenth in a series of weekly bulletins on the general in- 

 sect situation in Illinois (fruit insects excepted), prepared "by entomologists of the 

 University of Illinois College of Agriculture, Illinois Natural History Surveyed 

 cooperating agencies. It is designed to forewarn people in Illinois of impending 

 changes in insect activity and to suggest abbreviated control measures. These re- 

 ports indicate only general trends. Each individual should check his own fields to 

 determine local conditions. 



Corn leaf aphid control with insecticides will probably not pay from now on, 

 as infestations are declining. Shortly after pollination, corn plants become less 

 favorable for aphid survival. Winged ahpids develop and leave the plants; most of ^ 

 the wingless ones die. Also, both larvae and adult lady beetles that devour quanti- 

 ties of aphids each day are abundant in many fields. This week occasional fields 

 averaged as high as 20 or more lady beetles per plant. Other predators are also pres- 

 ent. Brown swollen, hardened aphids that have been killed by a wasp parasite are^ 

 also numerous. A fungus disease is also killing aphids. Hard rains have helped in 

 control. Only extremely late fields of corn not yet pollinated and not having these 

 natural controls will profit from insecticides. 



Several non-related observations can be made. The white specks remaining 

 on aphid-infested plants are the cast-off skins of aphids. The green maggots are^ 

 larvae of flower flies; they eat aphids. The sticky material on the corn leaves is 

 the aphid secretion called honeydew. The blackened appearance is a mold that grows 

 on this sugary honeydew. Some fields have many plants that were actually coated with 

 aphids and the tassel leaves turned brown. Many of these plants are stunted, the 

 internodes are shortened, and the leaves are yellow mottled. When cool weather ar- 

 rives this fall, such plants will turn purple, closely resembling those infected with 

 maize dwarf mosaic. Thus severe damage by aphids may be confused with maize dwarf 

 mosaic infection. 



Northern corn rootworm adults are very common in many cornfields throughout 

 the northern half of Illinois. These small green beetles are thick in some fields, 

 and they eat the silks of the corn. If pollination has occurred, the most they will 

 do now is to eat the tip of the ear. If pollination has not taken place, several 

 beetles per silk can interfere with pollination. (We refer to beetles on all silks 

 of one ear, not several beetles on one individual silk. We are sorry that we were 

 not more explicit last week. ) So if there are several beetles per silk and pollina- 

 tion is just beginning, an application of carbaryl (Sevin) or diazinon may pay. 



Southern corn rootworm adults are also known as spotted cucumber beetles. 

 They are yellow to green beetles with about 12 spots on their backs. Their young 

 also eat corn roots, causing the plants to lodge. The beetles also eat corn silks, 

 but ordinarily the problem is not so severe as with northern corn rootworm. 



Three pests of soybeans may soon be evident. Bean leaf beetles are red, 

 green or yellow beetles that ordinarily, but not always, have black spots on their 

 wings. Green cloverworms are green worms with white stripes, and they jump when 



, 



