The management of natural systems while often meeting with success has also led to unexpected and undesirable outcomes. Unfortunately, the ultimate result, desirable or undesirable, of such management programs may not be apparent until long after the control efforts have begun. This is particularly true for forest-defoliating species that exhibit long-period cycles such as the invasive gypsy moth, Lymantria dispar, which causes widespread damage in some years but is rare in others.  We studied the effects of spraying biocontrol agents on gypsy moth population dynamics using a series of field-tested and empirically parameterized mathematical models.  This allowed us to examine potential control strategies and assess long-term effects. In a non-spatial model, addition of biocontrol into the system decreases the amplitude between boom and bust portions of the cycle.  However, ill-planned biocontrol applications can help maintain pest populations at unexpectedly high numbers, which would result in constant forest defoliation. In a spatial two-patch model, where one patch is sprayed and the other is left untreated, there is considerable danger that migration between patches may drive the unsprayed population to levels that could also result in constant forest defoliation. It is often assumed that any control strategy that decreases pest populations in the short-term is beneficial, but our results show that undesirable outcomes over the long term may often occur. Thus, perturbations via management can have unexpected results, driving and maintaining populations at multiple levels including those far from desired management goals.

Population Cycles; Biocontrol; Lymantria dispar