The mild winter will certainly allow a few pest species to survive better than average because their populations are usually knocked back by cold winters--bean leaf beetle and slugs are two that jump to mind, so we will need to watch those populations. The odd winter has most of the state 50-200 degree-days or so ahead of average (Figure 1) and will no doubt push some early season pests to be active earlier than normal. In fact, the PA-PIPE (Pennsylvania Pest Information Platform for Extension and Education) system (choose the Public Map link to see the models) indicates that leading edge of alfalfa weevil and cereal leaf beetle populations are likely to be being active in the southern tier of counties. Cereal rust mites and feed on timothy (i.e., timothy mites) are not easily modeled like some other pest species and so are not included in the PA-PIPE; nevertheless, this species is almost certainly active and infested fields will need to be treated soon (at green up) to maximize the control potential of the insecticide application.
The bottom line, however, is that the influence of these temperatures on the majority of crop pests we face is not very predictable. For example, many insect pests that we face (e.g., potato leaf hopper, black cutworm) are migratory and come to Pennsylvania from southern states; therefore, our local weather will not influence their arrival much. To be certain of what is in your fields and understand local pest populations, growers will need to rely even more on regular bouts of scouting--get out in the field and see what is active! To direct this scouting effort, check the PA-PIPE, which can be used to track degree-days and expected development of some relevant pest species.
The wrong approach to dealing with pest uncertainty is getting ready to spray more pesticides. The best and most economics approach will be to watch fields closely, talk with others to learn what they are seeing, and stay tuned here for reports of pest activity.