Population Dynamics of Leafminers and 

 Their Parasitoids in IViassachusetts 

 Apple Orchards: 1999 Studies 



Baige Zhao, Starker Wright, and Ronald Prokopy 

 Department of Entomology, University of Massachusetts 



In the preceding article, we presented information 

 on the species composition of third-generation 

 leafminers found in 12 commercial and four abandoned 

 Massachusetts apple orchards during 1997, 1998, and 

 1999. Results showed that each year, all four 

 abandoned orchards and three of the commercial 

 orchards were dominated by spotted tentiform 

 leafminers (STLM). Conversely, each year seven of 

 the commercial orchards were dominated by apple 

 blotch leafminers (ABLM). Two of the commercial 

 orchards were dominated by ABLM in 1997 but by 

 STLM in 1 998 and 1 999. We concluded that the degree 

 to which apple is a preferred host of STLM relative to 

 ABLM and the degree to which STLM relative to 

 ABLM is susceptible to insecticides could be principal 

 factors associated with dominance by STLM vs. ABLM 

 but suggested that parasitoid species composition and 

 abundance might also be contributing factors. 



Here, we present information on the species 

 composition and abundance of leafminers and their 

 principal parasitoids for each of the three generations 

 of leafminers that occurred in 1999 in these 12 

 commercial and four abandoned orchards. 



Materials & Methods 



In June, August, and November of 1999, we 

 sampled 10 leaves on each of 30 trees in each 

 commercial and abandoned orchard for total numbers 

 of first-, second-, and third-generation mines, 

 respectively, in each 300-leaf sample. After taking each 

 sample, we collected as many infested leaves 

 (containing tissue-feeding mines) as possible during a 

 1 -hour search of the orchard up to a maximum of 1 00 

 mines per orchard for the first and second generations 

 and 300 mines per orchard for the third generation. 



Mined leaves were returned to the laboratory for 



examination under a microscope to determine presence 

 and identity of parasitoids and identity of leafminers. 

 A complete categorization of the extent of parasitism 

 of mined leaves would include presence of holes in 

 leaf tissue made by parasitoid adults seeking to feed 

 upon leafminer larvae as well as presence or evidence 

 of parasitoid eggs. Because such evidence of parasitism 

 was very difficult to determine with certainty, we 

 confined our confirmation of parasitism to presence 

 of parasitoid larvae, pupae (or their remains), and 

 adults. Consequently, the values presented here for 

 extent of parasitism of leafminers were undoubtedly 

 lower than actual percentages occurring in orchards. 



Results 



Data in Table 1 show the abundance of leafminers 

 in each generation in each orchard. Data in Table 2 

 show the species composition of leafminers and 

 percentages of leafminer larvae parasitized by the two 

 dominant parasitoids {Sympiesis tnarylandensis and 

 Pholetesor ornigis) in each generation in each orchard. 

 Owing to insufficient abundance of first-generation 

 mines in some orchards, there are some unfortunate 

 gaps in the data set for this generation of leafminers. 



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

 STLM was the exclusive (or nearly exclusive) 

 leafminer species present in each of the three 

 generations. In five of the commercial orchards (A, 

 D, F, G, I), STLM dominated in the second and third 

 generations. STLM dominated also in the first 

 generation in two of these orchards (A and I). ABLM 

 slightly dominated STLM in the first generation in 

 Orchard D, and no first-generation data were available 

 for Orchards F and G. In the other seven commercial 

 orchards (B, C, E, H, J, K, L), ABLM was markedly 

 dominant in the second and third generations as well 



14 



Fruit Notes, Volume 67, Summer, 2002 



