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DO FUNGICIDE RESIDUES AFFECT APPLE MAGGOT FLY EGGLAYING? 

 Susan B. Oppl, Susan L. Butkewich^, and Ronald J. Prokopy-^ 

 Department of Entomology 



In previous issues of FRUIT NOTES, we described some of our studies 

 on the effects of various substances on apple maggot fly egglaying. For 

 example, we found that a substance (pheromone) released by female flies 

 following egglaying deters other females from attempting to lay an egg in 

 that fruit (Vol. 42, No. 1). We also found that sodium chloride (table 

 salt) Vol. 45, No. 5) and acid rain (Vol. 48, No. 4) deter egglaying, 

 while calcium chloride has no such effect (Vol. 45, No. 5). 



Recently, we decided to test some of the fungicides commonly applied 

 to apples to control mid- to late-season diseases for possible effects 

 of their residues on apple maggot fly egglaying. We felt that an 

 egglaying deterrence from fungicides applied during the months of peak 

 apple maggot fly activity might affect grower choice of fungicides for 

 use against diseases. 



We tested at field rates 9 organic fungicides currently recommended 

 for apples and 1 fungicide (Bordeaux mixture) no longer applied to 

 apples. Unfortunately, our laboratory trials showed no effects of any 

 of the organic fungicides on apple maggot fly egglaying. Only the 

 inorganic fungicide Bordeaux mixture significantly deterred fly 

 egglaying (Table 1). Before the introduction of organic fungicides, 

 Bordeaux mixture was widely used as an orchard fungicide. However, it 

 is phytotoxic and is not compatible with many other pesticides, and thus 

 is no longer recommended for orchard use. 



It is also interesting to note that even the fungicides which left 

 visibly heavy residues on test fruit (such as sulfur) or had a 

 disagreeable odor (such as fenarimol ) did not deter fly egglaying. We 

 are reminded that insects may react in ways which differ dramatically 

 from what we might expect. 



Graduate student. Entomology 



Extension Technician 

 ^ Extension Entomologist 



