0.0 



7/2 7/17 7/30 B/23 9/10 



Collection period 



9/24 



Figure 1. Numbers of spiders collected per tree ia full second- 

 level and first-level IPM blocks during 1992. Means within 

 each date accompanied by a different letter are significantly 

 different at odds of 19:1. 



blocks during August and September, a conclu- 

 sion reinforced by laboratory findings (next sec- 

 tion). 



Insecticide and Miticide Effects 

 on Spiders 



To test the effects of insecticides and miti- 

 cides on spiders directly, a laboratory test was 

 conducted on the most common spider species 

 found in all six orchards: Araniella displicatta 

 (Araneidae). All individuals tested were imma- 

 ture, averaging 2 mm in size (the size found in 

 early September in the field). All were collected 

 at the same time in the same orchard. Spiders 



ity to pesticides. 



cation). Ten additional 

 jars were coated with 

 water as controls. 



After 9 hours all 10 

 spiders in the Thiodan 

 jars were dead, as were 9 

 of the 10 in Guthion jars. 

 None died in the Omite or 

 control jars, although one 

 spider died in the Omite 

 jar after 45 hours. 



These results indi- 

 cate that these insecti- 

 cides were highly toxic to 

 spiders, or at least to this 

 particular found species. 

 Omite, on the other hand, 

 was not very toxic to this 

 species of spider. It would 

 be inappropriate, how- 

 ever, to apply these find- 

 ings to all orchard pesti- 

 cide-use situations, in 

 that pesticide effects may 

 not be confined to pure 

 contact toxicity. Also, 

 many different spider 

 species exist and some 

 may differ from A. 

 displicatta in susceptibil- 



Effects of Herbicides on Spiders 

 on Apple Trees 



To determine if herbicide treatment of 

 ground cover affects the number of spiders on 

 trees, some trees in five second-level IPM blocks 

 were not treated with herbicide while a herbi- 

 cide treatment was apphed in May beneath 

 other trees. Two additional blocks (likewise 

 under full second-level IPM) at the University of 

 Massachusetts Horticultural Research Center 

 (HRC) in Belchertown also were employed in 

 this experiment. Herbicides vised included para- 



were placed individually in glass jars coated quat and simizine in the HRC blocks, and these 



with the substance to be tested. Ten jars were herbicides as well as Post™, amate, and 



coated with Guthion, 10 with Thiodan, and 10 Fusilade™ in the five second-level IPM blocks, 



with Omite (each at standard field rate of appli- The two HRC blocks consisted of dwarf trees 



Fruit Notes, Winter, 1993 



21 



