common names: Nitidulid Beetle, Oak Wilt Beetle, Sap Feeding Beetle
scientific name: Order Coleoptera, family Nitidulidae, several species
identification: Adults look like tiny rove beetles.
biology and life cycle: Nitidulids inhabit fungal mats beneath the bark of diseased red oaks (Quercus texana and Quercus shumardii). Infectious beetles emerge from the fungal mats and deposit oak wilt spores in wounds on healthy trees by feeding in sap.
habitat: Texas live oaks, red oaks, and blackjack oaks.
feeding habits: Sap from cuts or wounds on oak and other trees. Also feed on rotting fruit in the orchard.
economic importance: This beetle spreads the devastating oak disease called oak wilt (Ceratocystis fagacearum), which has killed thousands of live oaks and red oaks in Texas.
natural control: Keep trees in healthy condition so they can resist the beetle and disease. Mulch or maintain the natural habitat under trees.
organic control: The Texas Forest Service recommendation is to trench to separate the roots of infected trees from those of healthy trees and inject chemical fungicide into the trees. We do not recommend that approach. There is strong anecdotal evidence that the Sick Tree Treatment works to prevent the disease and save infected trees.
insight: Infestations cause fungal mats to form on red oaks only, not on live oaks. For that reason, live oak wood can be used for firewood without any worry. Red oak wood needs to be stacked in a sunny location and covered with clear plastic to form a greenhouse effect to kill the beetles and fungal mats. When oaks are ground into mulch, the aeration kills the pathogens and eliminates the possibility of disease spread.
Beetles in the family Nitidulidae, sometimes called sap beetles. These beetles have been
implicated as the primary carriers of fungal spores of the oak wilt pathogen to healthy trees.
Trees of highly susceptible red and white oak species wilt rapidly from the top down and are killed completely within four to six weeks. Moderately susceptible species wilt more slowly. Trees of species with low susceptibility may "wall off" the disease and survive with only partial death of branches.
Healthy trees are infected by fungal spores that enter wounds on branches and trunks. Insects such as sap beetles (Nitidulidae) and bark beetles (Scolytidae) are attracted to oozing sap from fresh tree wounds. The beetles become contaminated with fungal spores and are believed to be the primary agents of long-distance spread from diseased to healthy trees. Thus, the importation of all wood with bark is prohibited since it may contain contaminated beetles. The disease also spreads slowly from tree to tree via natural root graphs.