UPDATE ON THE RELATIVE TOXICITY OF ORCHARD 

 PESTICIDES TO THE PREDATOR MITE AMBLYSEIUS FALLACIS 



Susan L. Rutkewich and Ronald J. Prokopy 

 Department of Entomology 



In past issues of Fruit Notes we cited the relative toxicity of orchard 

 pesticides commonly used in Massachusetts apple orchards to the mite preda- 

 tor Amblyseius fallaci s in both laboratory (Vol. 43 (5): 14-18; Vol. 44 

 (5): 6-8) and orchard settings (Vol. 43 (4): 5-8). We have shown that 

 Massachusetts field populations of A. fallacis , an important predator of red 

 and two-spotted spider mites, are highly susceptible to field concentrations 

 of some pesticides such as Lannate* (methomyl), Cygon* (dimethoate) and the 

 synthetic pyrethroids (SPs), but can tolerate other pesticides like Guthion* 

 (azinphosmethyl ) , and Thiodan* (endosul fan) . 



The degree of tolerance or resistance this predator possesses can vary 

 from region to region depending on the history of chemicals applied in each 

 area. Resistant strains of A_^ fallacis have been found in orchards across 

 the country. In Michigan, New York, New Jersey and North Carolina, several 

 field populations of A^. fal lac is have been screened for resistance to 

 various pesticides. In' particul ar , at the Pesticide Research Center and 

 Department of Entomology at Michigan State University, Brian Croft and others 

 have evaluated pennPthrin-( Ambush* , Pounce*) resistant strains of A. fal lac i s 

 for cross resistance to other SPs and for resistance to insecticides in 

 other classes, i.e., organophosphates and carbamates. Successful establish- 

 ment of resistant/cross resistant predator mites in the field would provide 

 an important tool for IPM programs across the country. 



What alternatives exist for encouraging predator mite populations 

 today? At present the most effective strategy a grower can undertake is to 

 select pesticides and application time which have minimal effects on preda- 

 tors. Pesticides of high or moderate toxicity are not recommended in 

 orchards after bloom. Pesticides can be detrimental to A. f allacis if they 

 are applied when the predator is in the understory, i.e. diinng spring and 

 early summer, and later when the predator has moved up into the tree, i.e. 

 July through September. 



Here, we present the latest compilation of the relative toxicity of 

 pesticides commonly used in Massachusetts apple orchards to the predatory 

 m1te A. fal 1 ac is . The toxicity ratings have been arranged according to each 

 state where the infomation was obtained. The ratings provide comparison of 

 the predator's susceptibility to pesticides in different geographic loca- 

 tions. 



*Trade name 



