fcrred to a leaf nc.ir the center of the canopy of a 

 small non-frinting fig tree and allowed to forage 

 freely for 15 muiutes. The niinibcr of leaves vis- 

 ited was recorded. Immediately thereafter, each 

 fly was placed on a ripe hawthorn fruit, and pro- 

 pensity to lay an egg was observed. 



Results 



In our first test, conducted with no sugar added, 

 20, 80, and 100% of AMF died by contact toxic- 

 ity alone when confined in plastic cups treated with 

 0.5, 1.0, and 5.0% a.i., respectively, of imidacloprid 

 in paint (Table 1). None died at 0.1% a.i. of 

 imidacloprid. The only other toxicant causing 

 AMF mortality was fipronil, where 107o of AMF 

 died by contact toxicity alone after exposure to 

 5.0% a.i. of this material. Even though both 

 spinosad and sugar ester conceivably might be 

 somewhat toxic to AMF if ingested together with 

 sugar or when applied alone to foliage, neither 

 material caused any toxicity by contact alone when 

 mixed in latex paint. 



In our second test, results showed that in the 

 presence of sucrose, mortality of AMF was consis- 

 tently high (70% or more) on spheres treated with 

 imidacloprid, even after 12 weeks of sphere expo- 

 sure to outdoor weather in orchard trees (Figure 

 1). Provided that sugar was present, the dose of 



imidacloprid had little effect on AMF toxicity, with 

 2% a.i. being about as toxic as 16% a.i. at all evalu- 

 ation periods (3, 6, 9, and 12 weeks). In contrast, 

 in the absence of sucrose, toxicity of imidaclcjprid- 

 treated spheres to AMF did not exceed 15% at 12 

 weeks of orchard exposure, even at the highest dose 

 tested (16% a.i.). Results for fipronil roughly par- 

 alleled those for imidacloprid at 3, 6, and 9 weeks 

 of orchard exposure. However, at 12 weeks, even 

 in the presence of sucrose, lower doses of fipronil 

 (2 and 4% a.i.) yielded no more than 40% mortal- 

 ity of AMF. A dose of 8% fipronil was required 

 before toxicity approached that of 2% imidacloprid 

 at 12 weeks. In the absence of sucrose, toxicity 

 from contact with fipronil, as with imidacloprid, 

 was virtually nil at 12 weeks, irrespective of dose. 

 In our third test, results showed that only a 

 minority of AMF exposed to spheres treated with 

 2% a.i. imidacloprid and sucrose were capable of 

 foraging within a plant canopy after exposure, and 

 of those that could forage, an average of only one 

 leaf was visited for every three flies tested (Table 

 2). Moreover, only 6% of assayed AMF attempted 

 to oviposit in a hawthorn fruit. In contrast, al- 

 most all AMF exposed to spheres treated with 2% 

 a.i. fipronil were capable of foraging within a plant 

 canopy, with the average number of leaves visited 

 nearly equaling the number visited by AMF that 

 were exposed to spheres lacking pesticide. Also, 



Fruit Notes, Volume 63 (Number 4), Fall, 1998 



