remained at a rather low LM density throughout the 

 three years. Similarly, data in Table 2 show that in 

 each of the three geographical regions, at least one 

 sampled orchard was dominated by ABLM across the 

 three years and at least one other commercial orchard 

 was dominated by STLM across the three years. Thus, 

 neither the population density nor the species 

 composition of LM appeared to be affected by 

 geographical location within Massachusetts. 



In all, there were five commercial orchards (A, F, 

 G, I, L) wherein the density of third-generation mines 

 reached 100 per 100 leaves in at least one of the three 

 years (Table 1). In three of these five orchards (A, F, 

 I), the dominant species each year was STLM (Table 

 2). In the fourth orchard (G), ABLM dominated in 

 1997 but STLM in 1998 and 1999. In the fifth orchard 

 (L), ABLM dominated each year. In the remaining 



seven orchards (B, C, D, E, H, J, K), the 

 density of third-generation mines did not 

 reach 100 mines per 100 leaves in any of 

 the three years (Table 1). In six of these 

 seven orchards, the dominant species each 

 year was ABLM (Table 2). In the seventh 

 orchard (D), ABLM was distinctly 

 dominant m 1997 but STLM was distinctly 

 dominant in 1998 and 1999. Thus, the 

 highest densities of leafminers were 

 associated largely with dominance by 

 STLM, whereas lower densities were 

 associated largely with dominance by 

 ABLM. 



As summarized in Table 3, none of the 

 four abandoned orchards (M, N, O, P) 

 received an insecticide treatment against 

 LM during any of the three years, and five 

 of the commercial orchards (A, D, F, G, I) 

 received no insecticide treatment against 

 LM in 1997 and 1998, although four of the 

 five received such treatment in 1999. All 

 nine of these orchards were dominated by 

 STLM in 1998 and 1999. In contrast, seven 

 of the commercial orchards (B, C, E, H, J, 

 K, L) received an insecticide treatment 

 targeted against LM in two or all three 

 years. Each year, all seven of these orchards 

 were dominated by ABLM. 



Thus, no or infrequent spraying against 

 leafminers appears to be associated with the 

 nse of STLM to the status of dominance, 

 whereas frequent spraying seems to be associated with 

 dominance by ABLM. Our data are insufficient for 

 establishing a relationship between time since 

 application of an insecticide against leafminers and the 

 rise of ABLM to dominance, although the data in Table 

 3 for 1 999 for orchards A, D, G, and I suggest that such 

 a rise to dominance by ABLM does not occur during 

 the same year that insecticide is applied. 



Conclusions 



Results of this three-year study suggest that 

 dominance in species composition of LM in 

 Massachusetts orchards was (1) not associated with 

 any particular geographical region within the state, (2) 

 was apparently associated with LM density, and (3) 

 was apparently associated with frequency of insecticide 



Fruit Notes, Volume 67, Summer, 2002 



11 



