AELM, suggesting a possible preference of P. ornigis 

 for STLM. 



Conclusions 



Several of the data trends shown and discussed here 

 and in the preceding article for Massachusetts orchards 

 are similar to trends reported earlier by Chris Maier, 

 whose outstanding work on leafminers in Connecticut 

 orchards inspired our studies. Notable among the 

 trends for both Connecticut and Massachusetts are ( 1) 

 a strong tendency toward a shift in dominance from 

 ABLM to STLM with decreasing frequency of annual 

 insecticide treatment against LM, (2) a strong tendency 

 toward lower parasitism of LM in sprayed than 

 unsprayed (abandoned) orchards, and (3) generally 

 greater levels of LM parasitism by S. maiylandensis 

 than by P. ornigis, especially among populations of 

 ABLM. 



Parasitoids alone appear to be sufficient to exert 

 effective population suppression of LM in abandoned 

 orchards and may have contributed to population 

 suppression of LM in those commercial orchards 

 designated here as A, D, F, G, and L which received no 

 insecticide treatments against LM in 1997 and 1998. 

 Even so, four of these five STLM-dominated orchards 

 (A, D, G, I) did require a LM -targeted treatment in 1 999, 

 suggesting that parasitoids alone were insufficient to 

 effectively suppress STLM below potentially damaging 



levels. The lowest levels of LM parasitism found in 

 1999 were in orchards designated here as B, C, E, H, 

 J, K, and L, all of which were dominated by ABLM 

 and all of which received a LM-targeted insecticide in 

 1999 (all seven of these orchards also received a LM- 

 targeted insecticide in 1997 and/or 1998). 



The 89-fold level of first- to third-generation 

 population increase in STLM-dominated Orchard F in 

 1999 was explosive in comparison with the decrease 

 in average first- to third-generation population density 

 that characterized STLM-dominated abandoned 

 orchards in 1999. For reasons yet unknown but 

 possibly associated with apple being the principal host 

 of STLM and only one among many different hosts of 

 ABLM, unattended populations of STLM in 

 commercial orchards could represent a greater threat 

 than populations of ABLM. We hope to explore this 

 possibility in future research. 



A cknowledgements 



We thank the apple growers who participated in 

 this study: John Blanchard, Bill Broderick, Dave 

 Chandler, Dave Cheney, Dana Clark, Tony Lincoln, 

 Dave Shearer, Joe Sincuk, Tim Smith, Mo Tougas, and 

 Bob Tuttle. We are also grateful for the support of a 

 USDA Northeast Region SARE grant and state IPM 

 funds. 



it it it *k it 



Fruit Notes, Volume 67, Summer, 2002 



17 



