reduce or completely omit miticide sprays in Michigan and North 

 Carolina apple orchards without buildup o£ plant-feeding mites (red, 

 two-spotted, and apple rust mites). 



How was this achieved? First, it was established that popula- 

 tions o£ plant-feeding mites begin to cause injury when they reach 

 a level of 15 or more per leaf. If there are fewer than 15 mites 

 per leaf, then no detectable injury results from their presence. 

 In abandoned or unsprayed orchards, plant-feeding mites are scarce, 

 and rarely or never reach the econom.ic threshold level of 15 per 

 leaf. One of the reasons why they are scarce in abandoned orchards 

 is that they are eaten by predators, which are abundant in un- 

 sprayed trees. 



When organic insecticides were first used in apple orchards, 

 plant-feeding mites were not troublesome. The reason was that the 

 insecticides killed both the mite predators and the plant-feeding 

 mites. However, the plant-feeding mites rapidly began to develop 

 resistance to insecticides, and subsequently to miticides. The 

 ecology and behavior of mite predators is not the same as that of 

 plant-feeding mites and their resistance to pesticides was slow to 

 develop. Consequently, few mite predators were able to survive in 

 commercial orchards and plant-feeding mites became a major problem. 



What Croft and Rock have found is that certain species of mite 

 predators in Michigan and North Carolina orchards have now become 

 resistant to or tolerant of certain insecticides. When they em- 

 ployed these particular insecticides selectively and at the proper 

 time, the need for miticide usage was greatly reduced or completely 

 eliminated without buildup of plant-feeding mites to the economic 

 threshold. The insecticide-resistant mite predators did the job. 



In these and other publications, Croft and Rock are careful 

 to emphasize that maintenance of a sufficient number of insecti- 

 cide-resistant mite predators in the orchard is a very delicate 

 operation. It usually requires the continuous presence of at least 

 a few plant-feeding mites as a source of food for the predators, 

 and the balance can be upset by even minimum use of an insecticide 

 or miticide harmful to the predators. Certain fungicides and herb- 

 icides also were found to be toxic to the predators and could not 

 be used in the integrated control orchards. 



Can we apply the findings of Croft, Rock, and others, who 

 studied integrated pest control, to Massachusetts orchards? Yes, 

 we hope so - but first we must do some research. We need to sur- 

 vey which species of mite predators occur in our abandoned orchards. 

 This will tell us which predators thrive naturally in our state. 

 Then we need to survey our commercial orchards to determine which 

 of the naturally occurring predators, if any, have developed resis- 

 tance to which insecticides. In Michigan and North Carolina, the 

 predominant insecticide-resistant predator of plant-eating mites 

 in apple trees is a predacious mite called Amblyseius fallaais . 



