Our data infer that the biodiverse Christmas tree system, which uses specific low growing perennial and annual cover crops to attract and conserve beneficial arthropods, has high numbers of natural enemies throughout the season. Early in the season, ladybugs and syrphids are common. It is very important to have these predators present in the field early in the season, as this is when damage by twig aphids can be prevented. By around mid-July or so, the numbers of ladybugs and syrphids begin to drop (possibly as a function of prey presence), and other generalist predators, like spiders, increase in numbers.
We were particularly encouraged to find all life stages of ladybugs, syrphids, spiders and other predators, like lightning bugs, in our tree samples. Through this work, we realize that is it not one specific predatory insect that will make the difference in our system. Rather, it is the combined effect of many tyoes of beneficials, both insects and spiders that help to suppress pests in the biodiverse Christmas tree production system.
This study raises as many questions as it answers. For example, we found very high levels of spiders in our samples. What role do spiders play in suppressing Christmas tree pests? We also found many other predators, like lightning bugs (Lampyridae) that also appear to be important predators in the system, working mainly at night to feed on soft-bodied insects in the trees. We would like to determine the exact spacing parameters for various beneficials as related to the cover crop. For example, syrphid flies are excellent fliers. Thus, syrphids do not need the cover crop to be directly next to the Christmas trees in order for them to search and oviposit eggs in the trees. On the other hand, ladybugs, which do not disperse as readily or as far as syrphid flies, would need attractant plants to be nearby the Christmas trees in order for the ladybugs to search them.
Our data show that high numbers of beneficials are present in the biodiverse Christmas tree system. Beneficials that occur around the trees in the cover crops also occur in the trees as well. By encouraging the right types of plants in their cover crops, Christmas tree farmers can build beneficial insect refuges and breeding areas that will encourage beneficial insects to stay in a particular area. By using the biodiverse Christmas tree production system, we believe that Christmas tree growers could lessen the frequency and amount of pesticides applied to Christmas trees for pests, and still produce a high quality tree, while preserving the environment.