Abstract. Organochlorines. Metals. Conclusions and Recommendations. Acknowledgments. References. People have applied organochlorine insecticides to bats or their roosts, or both, to study the effects on the bats, to kill them, or kill pest insects. Studies of effects have shown that DDT and dieldrin are more toxic to bats than other organochlorines. They have also shown that DDT usually reduces colony size temporarily but that it rarely exterminates a colony. Application of DDT usually results in dead or dying bats lying outside the roost site, thus increasing the likelihood that people or pets will be bitten.