We have published a new study on how tree diversity affects invasive forest pests in the conterminous U.S. Our study was published in the Proceedings of the National Academy of Sciences. We examined the relationship between the number of native tree species and the number of nonnative forest pests. We found that both facilitation and dilution are occurring in a forest community. But their importance shifts with overall tree diversity. When tree diversity is relatively low, the number of pest species increases with increasing tree diversity. This supports the facilitation hypothesis. Greater tree diversity means more ecological niches for pests to exploit. But as tree diversity continues to increase, we saw a threshold where pest species begin to decrease. This is dilution. High tree diversity can mean fewer individual host trees. This can suppress invasion by limiting the resources that pest species need to support their populations. We hope these results will help to prioritize monitoring efforts for areas at risk for future pest invasions.