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A few materials that were of low toxicity to Aphidoletes eggs 

 were moderately or highly toxic to young larvae hatching from 

 treated eggs. Such early larval mortality was highest (571) for 

 Systox treatments, while Imidan, Thiodan, and Guthion (Fitchburg) 

 were of moderate toxicity (24 to 38%) to young larvae. 



Thiodan was found to be most toxic (46% mortality) to late 

 instar larvae while Systox was of moderate toxicity (321). The 

 fungicides Captan and Thiram, the miticides Plictran and Omite, 

 and the herbicide Glyphosate were all of low toxicity to Aphidoletes 

 eggs and larvae. 



These results show that Guthion, Systox, and Sevin had very 

 detrimental effects on the predaceous cecidomyiids from Belchertown. 

 Phosphamidon treatments were moderately toxic to Aphidoletes eggs 

 and young larvae hatching from treated eggs, thus resulting in over- 

 all high mortality. Zolone was the only insecticide tested that 

 had little effect on the eggs and young larvae of Belchertown ceci- 

 domyiids. However, Zolone has been found to be very highly toxic 

 to the most important mite predator in Massachusetts, Amblyseius 

 fallacis (Robert Hislop, personal communication) (see March-April, 

 1977 issue of Fruit Notes for more information on this mite preda- 

 tor). Thiodan and Imidan were moderately toxic to Belchertown 

 cecidomyiids and, according to recent lab tests by Robert Hislop, 

 of rather low toxicity to A. fallacis . Therefore, Imidan should 

 be the broad-spectrum insecticide of choice and Thioaan the aphi- 

 cide of choice if one desires good insect and aphid control while 

 allowing at least moderate survival and build-up of our most im- 

 portant aphid and mite predators. The more abundant these preda- 

 tors, the fewer pesticide applications that are needed. 



We emphasize that these findings are based on tests of a sin- 

 gle population of cecidomyiids which has its own unique genetic 

 structure and has been exposed over the years to a certain array 

 of pesticides. The genetic structure and pesticide exposure his- 

 tory of cecidomyiids undoubtedly varies from orchard to orchard. 

 Indeed there is some indication from our field observations that 

 cecidomyiid populations in certain commercial orchards in Massa- 

 chusetts may be more tolerant of Guthion treatments that Belchertown 

 populations. We are currently studying this aspect. 



In conclusion, we reiterate that the more abundant the aphid 

 predators, the fewer aphicide applications that are needed. 



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