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ACID RAIN AFFECTS APPLE MAGGOT FLY EGGLAYING 



Averill and Ronald J. I 

 Department of Entomology 



1 2 



Anne L, Averill and Ronald J. Prokopy 



Acid rain occurs when airborne sulfur and nitrogen oxides 

 originating from combustion of fossil fuels are washed to the 

 earth during rainfall as sulfuric and nitric acids. In addition 

 to being a popular topic in magazines and newspapers, this phen- 

 omenon is a complex political issue: although Massachusetts has 

 the most acidic precipitation in the country, many scientists be- 

 lieve that the bulk of our rain's contamination emanates from 

 Midwestern smoke stacks. Residents of the Northeast have become 

 progressively concerned and bitter as an increasing number of 

 scientific studies demonstrate detrimental effects of acid rain, 

 especially on aquatic ecosystems, soils, and crop and forest 

 vegetation. 



In the course of studies of apple maggot fly egglaying be- 

 havior, we noted a particularly intriguing effect of acid rain. 

 Our observations suggested that a host fruit exposed to acid 

 rain was less acceptable to the flies for egglaying than was an 

 unexposed fruit. To test this possibility more thoroughly, we 

 are hanging clean fruits in trees during each of this summer's 

 rains, with some fruits protected from rainfall by plastic hoods. 

 These fruits are brought to the lab, and by observing the number 

 of flies which attempt egglaying, we can evaluate the influence 

 of rain exposure on fruit acceptibility . Acidity (pH analysis) 

 of each rain event is determined by Dr. O.T. Zajicek of the Depart- 

 ment of Chemistry at UMASS. Thus far, most rains have fallen into 

 1 of 2 categories: those with pH values well below 4 (3.6-3.8) 

 and those with pH values above 4. These categories largely reflect 

 the dominant weather pattern at the time of the storm. Usually, 

 the more acidic contaminated storms (pH 3.6-3.8) move into our 

 region from the Midwest and the less contaminated storms move in 

 from elsewhere. The data available to date (Table 1) show that 

 apple maggot egglaying was not influenced when fruits were washed 

 by rains with a pH above 4, whereas egglaying was significantly 

 decreased when fruits were washed by rains of pH 3.6-3.8. 



This phenomenon may be explained by the fact that apple mag- 

 got flies have contact chemical receptors (hairs) which are loca- 

 ted on the bottom of their feet. Via these receptors, a fly may 

 receive cues emanating from the fruit to control steps in fruit 

 acceptance and egglaying. The presence of acids on the fruit 

 surface may interfere with perception of these cues, or may ac- 

 tually damage or destroy the chemical receptors. 



Whatever the explanation for our observations, it is possibly 

 to our advantage, and to the disadvantage of the apple maggot fly, 

 that acid precipitation is most severe in the summer months during 

 peak fly activity. 



2Graduate Student 

 Extension Entomologist 



