Growth of mold on spheres (Table 3) was found to oc- 

 cur more commonly on sugar/flour PTS than on wooden PTS. 

 This was a logical finding, given that the entire bodies of 

 sugar/flour spheres were constructed of food products (with 

 a small dose of preservative), all of which were subject to 

 mold growth. Through mid-season (six weeks), very few 

 wooden PTS exhibited significant mold growth (1.3%). In 

 fact, only 13.6% of wooden PTS in place through the entire 

 12-week trial had any mold present on the sphere surface. 



For sugar/flour PTS, a great number of 

 spheres exhibited mold growth through 

 4 weeks (32.7%) and 6 weeks (61.0%) 

 of field exposure, at which point all 

 spheres were replaced. In the second 

 6-week interval, fewer (26.2%) sugar/ 

 flour PTS developed mold, likely ow- 

 ing to greatly reduced rainfall and hu- 

 midity in the second half of the season 

 (Table 3). 



Residual Toxicity. After 6 weeks 

 of field exposure (Table 4), neither 

 wooden PTS nor sugar/flour PTS pro- 

 vided an acceptable level of AMF mor- 

 tality (30.7% and 26.5% kill, respec- 

 tively) prior to addition of feeding 

 stimulant. The implications of these 

 data are humbling, suggesting tliat af- 

 ter 6 weeks of field exposure, PTS of 

 either type were lethal to less than one- 

 third of arriving flies. Upon re-treat- 

 ment of spheres with feeding stimulant, 

 mortality of AMF after exposure to 

 wooden PTS was very good (75.7%). 

 However, sugar/flour spheres had ap- 

 parently lost a substantial amount of 

 toxicant (possibly lost to heavy rainfall 

 in the first half of the season), still yielding an unacceptable 

 level of AMF control (44.6%). 



As mentioned in the previous sections, we replaced all 

 sugar/fiour PTS at the mid-point of the season; wooden 

 spheres were left in place for the balance of the 12-week 

 season and only the sugar/wax caps were replaced. After an 

 additional 6 weeks of field exposure (Table 5), performance 

 of wooden PTS was nearly identical to performance at mid- 

 season: 4 1 .4% kill of exposed AMF prior to re-treatment with 



Table 4. Mortality of AMF after exposure to PTS. All PTS were retrieved from commercial orchards 

 at the mid-point of the season (six weeks field exposure) AMF were exposed (individually) to each 

 treatment and allowed to forage freely for up to ten minutes 



AMF mortality (%) 72 hours after exposure to: 



Treatment 



Wooden 

 PTS 



Sugar/Flour 

 PTS 



Control 



No sugar applied prior to fly exposure 



20% sugar solution applied prior to fly exposure 



30.7 

 75.7 



26 5 

 44.6 



2.1 

 0.0 



48 



Fruit Notes, Volume 65, 2000 



