Species Composition of Tliird- 

 generation Leafminers in IVIassachusetts 

 Apple Orchiards: 1997-1999 



Starker Wright, Baige Zhao, and Ronald Proliopy 

 Department of Entomology, University of Massachusetts 



In Massachusetts, leafminers (LM) have been a 

 consistent threat to the quality of apple foliage in 

 commercial orchards ever since their initial rise to 

 prominence in the late 1970s due largely to the onset 

 of resistance to organophosphate insecticides. Over 

 the past 10 years or so, LM in Massachusetts orchards 

 exhibited three rather distinctly different patterns of 

 population growth. In some orchards, growth has been 

 slight or at most moderate, never exceeding a threshold 

 requiring insecticide treatment. In other orchards, 

 growth also has been slight, owing to annual or biannual 

 application of a preventative insecticide spray against 

 LM. In still other orchards, populations have 

 undergone a period of explosive grov^h, followed by 

 rapid decline subsequent to insecticide treatment, only 

 to be followed by another period of explosive growth. 



Several factors might account for these observed 

 differences in characteristic form of LM population 

 growth. They include: (1 ) amounts, types and timings 

 of pesticides directed against other orchard pests, (2) 

 amounts, types and timings of pesticides directed 

 against LM, (3) the nature of the habitat adjacent to 

 commercial orchards, (4) the species composition and 

 diversity of parasitoids that can provide biocontrol of 

 LM, and (5) the species composition of LM themselves. 



In regard to the latter, through the 1980s, 

 commercial orchards in Massachusetts were dominated 

 by the apple blotch leafminers (ABLM) Phyllonorycter 

 crataegella, which is native to the USA and infests a 

 rather wide variety of plant species. During the 1990s, 

 however, we saw a rise in numbers of spotted tentiform 

 leafminers (STLM) Phyllonorycter blancardella, 

 which is an introduced species from Europe and infests 

 only apples and crabapples. 



Here, we report results of a study conducted from 

 1997-1999 aimed primarily at characterizing the 

 species composition of third-generation LM in 12 



commercial apple orchards in Massachusetts during 

 this three-year period. Our secondary aim was to 

 attempt to relate LM species composition with LM 

 population density and patterns of insecticide use 

 against LM. Other articles in this and future issues of 

 Fruit Notes will deal with LM populations as 

 influenced by parasitism, border area composition, and 

 type of perimeter-row cultivar. 



Materials & Methods 



In November in each of three years (1997-1999), 

 we sampled 10 leaves on each of 30 trees in each of 12 

 commercial orchards, pointing blindly toward the tree 

 canopy and picking the first leaf encountered by hand. 

 We counted the total number of third-generation mines 

 in the 300-leaf sample. After this, we picked as many 

 mine-infested leaves as could be found in a one-hour 

 search of the orchard (maximum of 300 leaves) and 

 returned them to the laboratory for examination of 

 pupae under a microscope. Pupae can be classified 

 according to LM species on the basis of the structure 

 of minute "hooks" present on the posterior end. In 

 1999, we also sampled mined leaves from four orchards 

 that had been abandoned for at least 5 years. 



Results 



To facilitate presentation of results, sampled 

 commercial orchards are grouped according to three 

 geographical areas in Massachusetts: Orchards A, B, 

 and C in the west, orchards D, E, F, and G in the center, 

 and orchards H, I, J, K, and L in the east. 



Data in Table 1 show that in each of these three 

 geographical regions, at least one sampled orchard 

 experienced a rather high LM density level in at least 

 one of the three years, and at least one sampled orchard 



10 



Fruit Notes, Volume 67, Summer, 2002 



