Effects of Mirex on Litter Organisms and Leaf Decomposition in a Mixed Hardwood Forest in Athens, Georgia

Mirex (dodecachlorooctahydro-1,3,4-metheno-2H-cyclobuta [cd] pentalene) in corncob grit bait and in spray form was applied to oak (Quercus alba L.) and dogwood (Cornus florida L.) leaf litter in mesh bags, on 20 5m by 5m plots. Macroarthropod fauna was monitored by capture in pitfall traps, and microarthropod populations were extracted from litter bags and counted. Ant presence on plots was tested by use of blank bait and molasses. Mirex in bait and spray form, and at the two levels applied, caused a significant acceleration in litter decomposition. The two leaf species as expected showed significantly different decomposition rates, and the slope of the ground surface on which the bags were placed was found to influence the decomposition process. The two leaf species differed in the amount of decomposition shown with mirex treatment, dogwood being more affected than oak. Ants were essentially removed from bait and concentrated spray plots up to 79 days, but ants had returned to all plots by the 334th day after treatment. The low spray treatment had no effect on the ant populations. Macroarthropods captured were spiders (Araneida), beetles (Coleoptera), millipedes (Orthomorpha gracilis), scorpions (Scorpionida), and centipedes (Scutigerella immaculata). Little difference was observed with treatment except with centipedes whose numbers appeared to decrease on the bait and concentrated spray plots. Microarthropod populations showed significant differences with treatment, at different times during the experiment, but no overall pattern could be detected that might explain the leaf decomposition acceleration noted with all treatments. Since microarthropod, macroarthropods and microflora are known to be involved in the decomposition, and since neither the microarthropods nor the macroarthropods could account for the change in decomposition then by extrapolation the groups most probably affected by the mirex would be the bacteria and fungi. These organisms were not monitored. It is speculated that mirex could have accelerated decomposition through its ability to induce mixed-function oxidase systems in the microorganisms. These enzymes are responsible for the breakdown of numerous xenobiotics or foreign compounds. If synthesis of more of these enzymes by fungi and/or bacteria allowed faster metabolism of the plant inhibitor, tannic acid, then decomposition could have received an early boost due to the growth of microorganisms usually limited by tannic acid.