SPOTTED TENTIFORM LEAFMINERS: BIOLOGY, MONITORING, AND CONTROL 



Ronald J. Prokopy, Robert G. Hislop, and William M. Coli 

 Department of Entomology 



INTRODUCTION 



From the early 1950's until 1978, spotted tentiform leafminers 

 (STEM) could occasionally be found in low numbers in unsprayed 

 apple trees in Massachusetts, but were rare in commercial Massa- 

 chusetts apple orchards. Since then, STEM have appeared in compara- 

 tively large and damaging numbers in some commercial orchards, esp- 

 ecially west of the Quabbin reservoir. Thus, in 1979 STEM mines 

 were found at levels of 0.1 or more per leaf in 12 of 13 orchards 

 sampled west of the Quabbin, but at this level in only 3 of 13 or- 

 chards sampled east of the Quabbin. 



There are 2 species of STEM in Massachusetts: Phyllonorycter 

 crataegella and Phyllonorycter blancardella . More than 901 of the 

 STEM sampled by us in Massachusetts in 1979 were P. crataegella . 



Recent studies by Dr. Richard Weires of the Hudson Valley 

 Fruit Laboratory in Highland, New York and by Drs . John Leeper and 

 Harvey Reissig of the Geneva, New York Experiment Station have clear- 

 ly shown that in New York, both these STEM have developed strong 

 resistance or tolerance to azinphosmethy 1 (Guthion) , phosmet (Imidan) , 

 phosalene (Zolone) , carbaryl (Sevin) and several other broad- spectrum 

 insecticides commonly used in orchards over the past decade or two. 

 On the other hand, the principal parasites of STEM continue to re- 

 main highly susceptible to these insecticides. The result is yet 

 another instance of pesticide- induced population explosion, compar- 

 able to the situation we have experienced with spider mites over the 

 past 3 decades. The pest, no longer influenced by the effects of 

 pesticide and freed from the presence of natural enemies, is able to 

 multiply very rapidly. 



Resistant populations of STEM were apparently first detected 

 in Columbia County, New York in 1974. Since then, such populations 

 have spread throughout most of the Hudson Valley and much of Connecti- 

 cut, and are now being carried into Massachusetts through natural 

 dispersal (often aided by warm southwest winds) and importation of 

 infested leaves in bins of apples from infested orchards. 



Even in cases when the original introduction of STEM into an 

 orchard may have consisted of only a few resistant individuals, popu- 

 lation buildup may be very rapid. Each female lays an average of 

 25 eggs, and there are 3 generations per year. Hence, if there 

 were no egg, larval, or pupal mortality, a single 1st generation 

 mated female in May could give rise to more than 15,000 STEM larvae 



