Could Bacteria in Nature be 

 Detoxifying Compounds for tlie 

 Apple IVIaggot Fly? 



Carol R. Lauzon, Bernard J. Robert*, Teresa G. Bussert, and 

 Ronald J. Prokopy 



Department of Entomology, University of Massachusetts 

 *Department of Plant & Soil Science, University of Vermont 



Insects are exposed, almost continuously, to 

 a variety of harmful compounds. Adults and 

 larvae may come into contact with harmful 

 synthetic chemicals, such as pesticides, or harm- 

 ful natural compounds, such as plant 

 allelocompounds (plant substances that often 

 protect it against pests). Insects may be exposed 

 to these harmful compounds either through 

 contact or through feeding. Either way, the 

 mechanisms for ridding these poisons from the 

 body are important survival processes. These 

 processes, referred to as detoxification mecha- 

 nisms, involve enzymes (proteins that facilitate 

 chemical reactions) which alter the structure of 

 the compound and make it more excretable (less 

 toxic). This can be achieved by removal or 

 addition of a chemical group. 



Generally, pesticides apphed by growers are 

 in amounts that overwhelm the insect's ability 

 to detoxify them. As time goes on, the pesticide 

 on plants is broken down by sunhght, wind, 

 rain, and other natural processes. Eventually, 

 residues may reach concentrations where the 

 insect C£in survive ingestion or contact. With 

 repeated exposure, the insect may evolve to 

 handle effectively a toxin in concentrations ear- 

 lier found to be lethal, i.e. develop pesticide 

 resistance. 



The apple maggot fly, Rhagoletis pomonelUt, 

 typically is controlled by two or three applica- 

 tions of azinphosmethyl (Guthion ), an orga- 

 nophosphate that is a potent inhibitor of cho- 



Unesterase, an enzyme responsible for normal 

 nervous system functioning. Azinphosmethyl 

 also is used to control other orchard pests such 

 as codling moth. Although no information exists 

 to date regarding resistance to azinphosmethyl 

 for the apple maggot fly, resistance has been 

 reported for codling moth. 



Mechanisms of insecticide resistance tradi- 

 tionally have been examined using genetic tech- 

 niques focused on resistant individuals and cre- 

 ation of models of gene flow between resistant 

 and susceptible insects. Less attention has been 

 paid to the potential involvement of bacteria 

 either within or on host plants or within insects 

 in the development of insecticide resistance. 



Interestingly, enzymes in bacteria capable 

 of converting toxic compounds into less toxic 

 compounds that are more easily excretable in- 

 clude the same enzymes that insects themselves 

 use in detoxification. In fact, many bacteria can 

 detoxify compounds internally or secrete en- 

 zymes responsible for metabolizing foreign com- 

 pounds into their surrounding environment. 

 Numerous reports exist on the abilities of cer- 

 tain species of bacteria to degrade and detoxify 

 a variety of compounds, including 

 azinphosmethyl and plant allelocompounds. 



Here we report on studies designed to deter- 

 mine if bacteria associated with the apple mag- 

 got fly could degrade, and subsequently detoxify, 

 azinphosmethyl and plant allelocompounds 

 likely to be consumed by this insect. 



Fruit Notes, Summer, 1994 



