Hunting Spiders in Second-stage 

 IPM Apple Orchard Blocks 



Ronald J. Prokopy, Margaret M. Christie, James Gamble, 



David Heckscher, and Jennifer Mason 



Department of Entomology, University of Massachusetts 



As pointed out in a recent review by Nyfeler and 

 Berg (1987), spiders are among the most abundant 

 predators of insects in terrestrial ecosystems. There 

 are 2 principal kinds of spiders. One kind builds 

 webs, such as web-weaving and funnel web spiders. 

 In some natural grassland communities, web-build- 

 ing spiders have been estimated to capture an aver- 

 age of 200,000 insects per acre per day, thereby 

 exerting a strong degree of biological pest control. 

 The other kind of spider does not build webs but 

 instead hunts for prey. These include jumping 

 spiders and wolf spiders. These too can have a 

 powerful biological control effect in undisturbed 

 habitats. 



Over the past 2 decades or so, fairly extensive 

 surveys of spider populations have been undertaken 

 in commercial and abandoned apple orchards in 

 several regions of North America (Dondale et al., 

 1979; McCaffrey and Horsburgh, 1980; Bostonian et 

 al., 1984). Not surprisingly, the general conclusion 

 is that spiders, particularly hunting spiders, are con- 

 siderably more abundant in unsprayed than sprayed 

 orchards. Unfortunately, outside of laboratory stud- 

 ies under artificial conditions, little is known about 

 the kind of prey consumed by spiders in orchards. 

 Suspected prey include aphids, leafroller moths and 

 larvae, leafhoppers, thrips, mites, and even benefi- 

 cial insects such as lacewings and ladybird beetles. 



As a first step toward acquiring 

 better knowledge of the potential 

 role of spiders as biological pest 

 control agents in Massachusetts 

 apple orchards, in 1990 we com- 

 pared the relative abundance of 

 hunting spiders in 12 blocks of com- 

 mercial apple trees (2 to 3 acres 

 each) that received no insecticide 

 after early June under full second- 

 stage IPM practices [Fruit Notes 

 55(l):4-9] with abundance in 12 ad- 

 jacent blocks that received 2 to 3 in- 

 secticide sprays after early June 



under normal first-stage IPM practices. To estimate 

 spider abundance in each block in early August and 

 again in early September, we tapped 3 branches on 

 each of 10 trees per block to dislodge hunting spiders, 

 which fell onto a framed cloth (2x2 feet) held 

 beneath the branch. 



The results (Table 1) show that in early August, 

 hunting spiders were slightly but not significantly 

 more abundant in second-stage than first-stage IPM 

 blocks. By early September, hunting spiders had 

 more than tripled in abundance in the second-stage 

 IPM blocks and were more than double the number 

 there compared with first-stage IPM blocks. 



Thus, like mite predators and leafminer parasi- 

 toids [Fruit Notes 55(l):4-9], hunting spiders may 

 build to higher populations in Massachusetts apple 

 orchard blocks free of insecticide spray after early 

 June compared with blocks receiving insecticide in 

 July and August. We do not know the principal type 

 of prey consumed by spiders on the trees that we 

 sampled. We believe, however, that the prey may 

 have included summer leafroller larvae and leafhop- 

 pers. Hence, we plan in the future to explore in 

 depth the effectiveness of spiders as predators of 

 leafroller larvae and leafhoppers and the role of 

 orchard understory cover in promoting buildup of 

 not only mite predators but also of spiders. 



Table 1. Average number of sampled hunting spiders per 

 orchard block. 



Time of sampling 



Second-stage 

 IPM blocks 



First-stage 

 IPM blocks 



Early August 

 Early September 



2.6 a* 

 8.6 a 



2.1a 

 3.9 b 



*Values within the same row followed by a different letter 

 are significantly different at odds of 19:1. 



Fruit Notes, Winter, 1991 



13 



