We have recommended a form of integrated control, or insect pest management, for 

 alfalfa-weevil control for the past three years. We encouraged fall applications 

 of insecticides, or spring applications that would interfere the least with the 

 natural enemies of this pest. 



Two new insecticides, carbofuran (Furadan) and Supracide, control alfalfa weevils. 

 We have tested these materials extensively and recommend their use for November ap- 

 plication to control adult weevils. However, if these insecticides are used to con- 

 trol alfalfa weevil larvae in the spring, apply them only at half the minimum, la- 

 belled rate. 



To some, our reasoning may seem odd. But these conclusions were reached after 

 making extensive observations. 



First, tiny parasitic wasps deposit their eggs on alfalfa weevil larvae. The small 

 grubs that hatch live inside the weevil larvae. Parasitized alfalfa weevils live 

 for some time, but feed very little. We have seen as high as 80 percent of the 

 larvae parasitized in some fields of alfalfa; in past years, 50- to 70-percent lev- 

 els were common. These wasps have been helping to control the alfalfa weevil popu- 

 lations . 



Second, in order to maintain this parasitic wasp population some alfalfa weevils 

 must remain as a reservoir for the wasps. If we kill these natural enemies with 

 insecticides or kill 95 percent or more of the alfalfa weevils in a large area 

 with insecticides over a period of time, the parasites will be eliminated by the 

 chemicals or by the lack of any alfalfa weevil larvae to feed on. Without the 

 help of these parasites, it might be necessary to spray several times. At pres- 

 ent, one application is usually sufficient. 



To maintain the wasp parasites so they will help control alfalfa weevils, a reason- 

 able but noneconomic number of the alfalfa weevils must remain for the wasps to 

 feed on. This is one step in integrated insect control or insect pest management . 

 This principle is effective for controlling field crop insects, since 75- to 85- 

 percent control will reduce the number of insects to none cone conomic levels and will 

 allow natural enemies to maintain their relative balance in the environment. 



Years ago, we would probably have encouraged the use of these two chemicals at 

 high rates. With the knowledge we have now, however, it is clear that this would 

 have been unwise. At high rates, Carbofuran and Supracide are so effective on 

 alfalfa weevils that no parasites remain. Thus, they should be used only at low 

 rates in order to reduce weevil larvae to a noneconomic level while retaining the 

 weevils' natural enemies. This practice will also reduce insecticide costs with- 

 out yield loss. The insecticides we have recommended in the past do just this. 



Apply an insecticide next November to kill adults. This will decrease egg laying 

 during the fall, winter, and spring. Sprays applied in the spring usually are not 

 needed; and again, this practice will maintain a suitable number of parasites. Large 

 alfalfa producers use this method in order to avoid hurry-scurry in the spring dur- 

 ing planting season for corn and beans. 



In many cases, there is no information on naturally occuring biological factors 

 that help suppress the populations of insect pests. Yet, ignoring known biolog- 

 ical controls, as with the alfalfa weevil, is unsound and can only lead to a 

 greater use of pesticides and to additional legal restrictions on their use. 



