-5- 



LABORATORY REPELLENCY OF ORCHARD PESTICIDES TO THE MITE PREDATOR 



AMBLYSEIUS FALLACIS 



1 2 2 



Robert Hislop , Peter Auditore , Bonnie Weeks 



3 

 and Ronald Prokopy 



For the past four years, we have been evaluating the impact 

 o£ orchard pesticides on the survival of Amblyseius f allacis , 

 the most important spider mite predator in Massachusetts apple 

 orchards (FRUIT NOTES 43(4): 5-8; 43(5): 14-18; 44(5): 6-8). In 

 our laboratory and field trials, we found that A. fallacis could 

 readily survive exposure to field rates of several key orchard 

 pesticides, including phosmet, azinphosmethyl , endosulfan, and 

 captan. However, in certain commercial orchards sprayed with 

 these materials, we observed occasional buildup of red or two- 

 spotted spider mites. We theorized that application of such 

 pesticides at a time when spider mites were building could actu- 

 ally enhance buildup by repelling A. fallacis from treated areas. 

 Recently, we explored this possibility of pesticide repellency 

 to A. fallacis in laboratory tests, and we present here our find- 

 ings. 



Our tests were conducted in the following manner. First, 

 we sprayed one half of a 2- inch-diameter bean leaf disc with 

 pesticide and allowed the residue to dry. Next we placed 15 two- 

 spotted mite eggs (previously sprayed with the same pesticide) on 

 the sprayed half of the disc, and placed 15 unsprayed eggs on the 

 unsprayed half. After two hours, we placed one adult female 

 A. fallacis on each disc, incubating all discs for 14 days. Each 

 Jay during the incubation period, we recorded three types of 

 information: (a) the number of two-spotted mite eggs consumed by 

 A. fallacis (consumed eggs were replaced daily) ; (b) the location 

 of each A. fallacis female every two hours from 8:00 AM to 6:00 PM; 

 and (c) the number and location of all eggs laid by A. fallacis . 

 We replicated each test 14 times. 



Our results are presented in Table 1. Compared with the un- 

 sprayed halves of bean leaf discs, the presence of residues of 

 phosmet, azinphosmethyl, captan, or Dikar on the sprayed halves 

 resulted in substantially lower consumption of spider mite eggs 

 by A. fallacis females. Residues of endosulfan, dodine, inert 

 carrier powder, or distilled water had little or no such effect. 

 In addition, residues of phosmet, azinphosmethyl, captan, and 

 Dikar resulted in substantially less oviposition and substantially 

 reduced presence of A. fallacis on treated sites. To a lesser 

 extent, this was truF ot endosulfan and inert carrier powder 

 residues as well. 



1 



Presently Research Technician, Department of Entomology, University 



of California at Berkeley 

 2 



Work Study Student, Department of Entomology 

 3 



Extension Entomologist 



