How Reliable Are Sticky Red Rectangle 

 Visual Traps for Monitoring 

 Leafminer Adults? 



Ronald Prokopy, Jennifer Mason, and Starker Wright 

 Department of Entomology, University of Massachusetts 



The newly-approved insecticide Provado™ against 

 leafminers offers hope that we now have for the first 

 time an effective and safe leafminer control agent that 

 is not harmful to beneficial predators and parasites. 

 Recent research in New York suggests that a single ap- 

 plication of Provado at petal fall may be all that is nec- 

 essary to prevent leafminer damage throughout the 

 growing season. 



Deciding whether or not a petal-fall application of 

 Provado is needed requires estimating the size of the 

 leafminer population prior to the appearance of mines, 

 which usually do not become evident until two or three 

 weeks after petal fall. This means that it is necessary 

 to sample either leafminer adults or eggs prior to petal 

 fall to gain an estimate of population size. New York 

 researchers and extension personnel have long empha- 

 sized that monitoring the abundance of eggs will give a 

 more accurate prediction of numbers of mines than 

 monitoring the abundance of adults. We concur with 

 this conclusion; however, our experience has shown that 

 considerable training is required for a grower to be cer- 

 tain of the identity of leafminer eggs, particularly 

 hatched eggs. A much simpler though less accurate 

 method involves sampling the abundance of adults us- 

 ing visual traps. These traps are sticky red rectangles 

 stapled to south sides of apple tree trunks at the green 

 tip stage of bud development. 



Here, we present data for four years (1991-1994) 

 during which we counted average numbers of first-gen- 

 eration leafminer adults on trunk traps in blocks of or- 

 chard trees and peak numbers of first-generation mines 

 in these blocks. Our intent is to portray the degree of 

 probability with which captures on trunk traps can pre- 

 dict population levels of miners. 



Materials and Methods 



Our study was conducted in 12 first-level and 12 

 nearby second-level IPM blocks, each 6-10 acres. At 

 green tip, we stapled a sticky red rectangle (Pest Man- 

 agement Supply Co., Amherst, MA) at knee height to 

 each of five trees per blocks, one near the center of the 

 block and one near each comer. We assessed cumula- 

 tive numbers of adults captured on traps per block 

 through tight cluster and through pink. We also as- 

 sessed peak numbers of first-generation mines by sam- 

 pling 20 leaves on each of 10 trees per block at a time 

 when miner abundance had reached its peak. We ex- 

 cluded all data for blocks in which an insecticide spray 

 was applied against first-generation adults or miners, 

 as such treatment could have altered dramatically the 

 relationship between adults and miners. 



We express our findings in terms that the probabil- 

 ity of cumulative captures of adults at tight cluster or 

 at pink will predict the need to treat with insecticide 

 before bloom or at petal fall, based on a threshold of 

 seven mines per 100 leaves at the peak of first-genera- 

 tion miners. Put into other words, our findings are pre- 

 sented in terms of the power of trunk traps to predict 

 the need to treat against first-generation adults or eggs 

 to prevent first generation larvae from exceeding a 

 threshold level that could result in eventual crop dam- 

 age if leafminers were to go untreated throughout the 

 season. The first-generation larval threshold of seven 

 mines per 100 leaves is targeted at Mcintosh and is 

 based on an expected eight-fold population increase from 

 first to second generation and a five-fold increase from 

 second to third generation (a 40-fold increase overall, 

 which is characteristic of most years). Our experience 



Fruit Notes, Spring, 1995 



