Slash pine flower thrips, Gnophothrips fuscus (Morgan) (13, 18, 19)

BIOLOGY. - Knowledge of the life history of the slash pine flower thrips is incomplete. It is likely that this thrips occurs throughout the Eastern United States (see wavy area of distribution map). Injury to conelets, however, appears to be restricted to slash pine (see unlined red area of distribution map).

The slash pine flower thrips damages or kills female buds and flowers during a limited period from January through mid-February. The minute insects hide among the bracts or scales and are seldom visible. Pollinated flowers quickly become leathery enough to resist additional thrips feeding, but the more severely damaged conelets continue to abort. This thrips has also been noted on succulent new shoots of slash and loblolly pines during the summer.

INSECT IDENTIFICATION. - The adults are comparatively large thrips, about 2 mm long, and very dark-brown to black. They can be either winged or wingless.

Adult (25X)

DAMAGE IDENTIFICATION. - Damaged female flower buds have resin flowing from wounds at the tips and between the crevices formed by abutting vegetative buds. Severely damaged buds often abort.

Once the buds open, the thrips scrape the tender scales and bracts of the female flowers, leaving tiny, barely visible abrasions marked by beads of resin. Individual scales and bracts are often destroyed, and if damage is severe the flower shrivels and dies. Female flowers sustaining sublethal damage develop into mature cones the following year, but these cones are crooked and gnarled, with areas of sunken, deformed scales.

Damage to conelets. (1X)

Damage on developed cones. (1X)

IMPORTANCE. - While the slash pine flower thrips damages and destroys female flowers only on slash pine, it is often very destructive in seed orchards of this species. Flower mortality as high as 45 percent has been recorded. In addition, both total and filled seed yields from cones that develop from flowers sustaining sublethal damage are often reduced by more than 50 percent.