Prior to 1st 1st to 2nd 2ncl to 3rd 



Insecticide Application 



After 3rd 



D Pyramid 

 □ Cylinder 

 ■ % Injury 



Figure 2. Captures of plum curculios per trap for two unbailed trap types and percent fruit injured by plum curculio 

 before the first insecticide application, between the first and second applications, between the second and third 



issue). 



Evei7 3-4 days from petal fall until five weeks af- 

 terward (the peiiod of fruit susceptibility to PC injury), 

 we examined 15 fruit on each of the seven perimeter 

 trees of each block. The number of PC egglaying scars 

 was recorded, and scarred fruit were allowed to re- 

 main on the tree. At each sample date, captures of PC 

 were recorded for each trap, and all captured PCs were 

 removed from traps and returned to the laboratory. All 

 blocks were treated according to the growers' stan- 

 dard orchard management practices, receiving two to 

 three applications of Guthion or Imidan at 9- to 14-day 

 intervals beginning at petal fall. 



Results 



We combined data for the two blocks of each plant- 

 ing density for each orchard and categorized fmit in- 

 jury and trap capture data according to spray interval. 

 The data (Table 1, Figure 2) show that PC egglaying 

 injury was very light in all blocks prior to the first in- 

 secticide application. Injury to fruit increa.sed sharply 

 between the first and second spray, and increased fur- 

 ther between the second and third spray. Interestingly, 

 PC damage to fruit subsided in most blocks after the 



third spray, but in a few blocks of high density trees, 

 there was a flurry of PC egglaying activity in mid-June, 

 after the final spray. 



Captures of PCs by unbaited black pyramid traps 

 were greatest prior to the first insecticide application, 

 decreased moderately between the first and second 

 spray, and decreased substantially after the second 

 spray (Table I, Figure 2). In fact, in several blocks 

 which continued to accumulate substantial PC damage 

 after the second insecticide application, not a single PC 

 was captured during this interval by unbaited pyramid 

 traps. A similar trend occurred for captures within the 

 tree canopies by unbaited black cylinder traps (Table 

 I , Figure 2). 



Conclusions 



Results of the 1998 field trial of unbaited PC traps 

 confirm our findings of 1 996 and 1 997. For commer- 

 cial use, captures of PC in unbaited trunk-mimic or twig- 

 mimic traps are not accurate indicators of the need for 

 or timing of insecticide applications. If development of 

 traps for other species related to PC (such as cotton 

 boll weevil and sugar cane weevil) can be used as a 

 guide, then the most effective trap for PCs should be 



Fruit Notes, Volume 63 (Number 3), Sui 



1998 



11 



