-9- 



In our first experiment we allowed equal numbers of red and two- 

 spotted spider mites to infest separate 1/2 inch diameter apple leaf 

 discs for 2 days, after which all spider mite prey (including eggs) 

 were removed. Each leaf disc was then placed in a simple, single 

 choice observation chamber. We then placed a single starved A. 

 f allacis female at the edge of the chamber and allowed it to enter 

 and leave the disc at will. Data and observations were recorded 

 over a ten-minute time period. The results (Table 1) show that A. 

 f allacis females spent an average of 312 seconds per visit on discs 

 having previous two-spotted mites compared with only 58 seconds per 

 visit on discs having no previous prey (an approximate 5-fold dif- 

 ference) and 156 seconds per visit to discs having previous red mites 

 (a 2-fold difference). These data strongly suggest that both species 

 of spider mites deposit substance(s) that function to arrest host 

 searching Aj_ f allacis , and that the substance (s) deposited by two- 

 spotted mites was more than twice as active as that deposited by red 

 mites. In this experiment we noticed that a large amount of silk (a 

 white thread-like material very similar to the sort of silk spun out 

 by spiders) was left behind by the two-spotted mites. We suspected 

 that this silk might be playing a role in the observed behavior of 

 A. f allacis . 



TABLE 1. FREQUENCY AND LENGTH OF VISITS BY A^ f allacis FEMALES TO 

 APPLE LEAF DISCS HAVING PREVIOUS PREY. (20 replicates) 



Avg. no. A. fallacis Avg. time 



visits per apple (seconds) per 



Previous prey leaf disc visit on disc 



Two-spotted Mites 1.5 312 



European Red Mites 2.6 156 



None (check 3,4 58 



Therefore, in our second experiment, we examined the possible 

 influence of two-spotted mite silk on the searching behavior of A. 

 f allacis . We manually placed the silk spun by 50 two- spotted mites 

 over a 24-hour period onto 1/2 inch diameter filter paper discs. Each 

 disc was placed in the observation chamber with a single starved A. 

 fallacis female and data recorded as before. 



The results (Table 2) show that host searching A^ fallacis females 

 spent 142 seconds per visit on discs containing two- spotted mite silk, 

 compared with 12 seconds per visit on discs having no silk (a 12-fold 

 difference). This result strongly suggested that physical and/or 

 chemical properties of two-spotted mite silk function to arrest host 

 searching A. fallacis females. 



