Pine tip moths
Family: Tortricidae, Pyralidae
Description and life history
Southwestern pine tip moth
The southwestern pine tip moth (Rhyacionia neomexicana) is native to the western United States and is found in Arizona, New Mexico, Utah, Colorado, the Dakotas, Montana, and Nebraska. Adults of the southwestern pine tip moth have a wingspan of about 2.4 cm (0.9 inches) and two distinct black lines on the outer portion of the forewing, though they may be faint on some individuals. The inner portion of the forewings are irregularly banded with bars of dark grey, black, and dark red scales, and the hindwings are grey. Females are slightly smaller than males.
The eggs of southwestern pine tip moth are elliptical with a convex upper surface and flat underside. The eggs are initially green-yellow but gradually change to orange-yellow and red-orange as the embryo develops. After hatching, larvae are yellow-orange with a dark brown or light tan head capsule. Larvae develop through five instars and reach a length of roughly 12-16 mm (0.5-0.6 inch) in length when mature.
Pupation occurs in silken cocoons attached to root collars of the host tree. Pupae measure about 7-10 mm (0.3-0.4 inches) long and are initially golden yellow or yellow-brown. Mature pupae are dark yellow or red-brown, and at this stage the two black streaks of the forewings are usually visible on the developing pupa. Pupae of the southwestern pine tip moth also have a prominent frontal horn or ridge on the head.
The southwestern pine tip moth overwinters as a pupa, and adults emerge the following spring as early as late March, with peak flights occurring as early as mid-April. Beginning in April, adults mate and the females lay eggs singly or in rows on the inner surface of one year old needles in the upper three foliage whorls. The eggs hatch about two weeks later, and larvae either mine into the needles or move to new shoots. Mining near shoots causes pitch to flow from wounds, which larvae mix with silk to form semi-transparent tents. Larvae can enlarge the tents to encompass the bases of several needles, which become severed and drop after turning yellow or brown. Feeding continues in the shoot and progresses upward from below the bud, and frass often accumulates with dry needles, pitch tents, and loose webbing on the outer surface of the shoot. Larvae exit shoots in early summer and overwinter in the soil by constructing pupation chambers about 2-3 cm (1 inch) deep, attached to the root collar of the tree.
Zimmerman pine moth
The Zimmerman pine moth (Dioryctria zimmermani) is native to the eastern United States and has become established in certain parts of Colorado. Adults of Dioryctria spp. are rarely observed and often difficult to distinguish between species. These moths are typically grey with white zig-zag markings on the forewings and measure about 15 mm (3/5 inch) long. Mature larvae are 15-25 mm (3/5-1 inch) and can be white, pink, orange, light green, or light brown with dark spots arranged in rows.
Austrian and Scotch pines are particularly susceptible to attack by the Zimmerman pine moth. The species overwinters as an immature caterpillar in a cocoon, which serves as a hibernaculum until the following spring. Between late-April or early May, the caterpillar emerges and begins tunneling into branch tips and shoots of the host tree. Later in the season, the caterpillars attack the base of branches and are often found underneath masses of pitch. Mature caterpillars remain in the tunnel to pupate, and the adult emerges in late July and August. Eggs are laid near wounds and hatch about a week later. Newly hatched caterpillars feed for a short period before excavating a hibernation chamber.
Larvae of D. ponderosae have a light brown head capsule and pale yellow or pink bodies. The larvae reside beneath masses of pitch and undergo four molts before pupating in a chamber of pitch and silk. This species sometimes requires two years to complete its life cycle.
Larvae of D. albovittella have light brown bodies and a dark brown head capsule that measures up to 19 mm (3/4 inch) long. Larvae overwinter on bark in silk cocoons and begin mining in unopened terminal buds in mid- to late-May. As the larvae grow, they cause more extensive injury as they spread to new tissue, cones, or shoots. Pupation occurs in late spring, and peak adult flights tend to occur in late July and early August.
- Several moth species can infest pines in Colorado. The southwestern pine tip moth infests ponderosa, mugo, foxtail, and Scotch pines, while the Zimmerman pine moth, Dioryctria ponderosae, and Dioryctria albovittella collectively infest pinyon, ponderosa, lodgepole, Austrian, and Scotch pines.
- Destruction of terminal buds due to southwestern pine tip moth can lead to increased lateral shoot growth, and repeated infestations can cause trees to have a bushy appearance with many lateral branches or stems. Tunneling of Dioryctria spp. causes masses of pitch to form on wound sites.
- Young, recently planted trees or stressed trees in urban areas are the most susceptible to these pests. There are several management options available, such as maintaining tree health, supporting resident populations of natural enemies, and applying insecticides.
Adult of Rhyacionia spp. Note the black line on the hind tip of the forewing. Image credit: Whitney Cranshaw, Colorado State University.
Caterpillar of the Zimmerman pine moth. Image credit: Cliff Sadof, Purdue University
Pine terminal injured by feeding of a pine tip moth (Rhyacionia spp.). Note the production of pitch at the terminal bud. Image credit: John Guyon, USDA Forest Service, Bugwood.org
Tree with excessive branching caused by feeding of Rhyacionia spp. Image credit: Terry S. Price, Georgia Forestry Commission, Bugwood.org
Young, recently planted seedlings are highly susceptible to infestations of southwestern pine tip moth. This species tends to be most problematic in landscape trees rather than forest trees, and larvae can destroy entire shoots. When the terminal bud is destroyed, increased lateral shot growth and new bud formation below the damaged shoot may be observed, which can produce a bushy tree with multiple stems. Repeated attacks can decrease tree growth and cause severe deformation of the host tree, including crooks, forks, multiple stems, and spiketops that occur simultaneously and remain years after the attack.
Larvae of the Zimmerman pine moth tunnel into the upper portions of the tree trunk and branches, forming irregular wounds under the bark that are most concentrated where branches meet the trunk. Popcorn-like masses of pitch may collect on the surface of such areas, and the pitch on recent injuries can often be pulled away to expose the tunnel. The pitch hardens over time and may remain on the tree for over a year after the injury occurred. Feeding of Zimmerman pine moth larvae can weaken branches and cause limbs to break from the tree.
Generally, trees less than 6 m (20 ft) tall in urban areas are highly susceptible to attack by Dioryctria spp. that target the trunks of young trees, larger branches, and limbs. These moths rarely cause problems on large trees or in forest environments, and most feeding injuries are inflicted over the summer. Gouges in the trunk and branches can exude pitch, and infestations of Dioryctria spp. can also expose host trees to secondary infestations of Ips beetles.
Practices that promote rapid tree growth, such as thinning overstocked stands, can reduce the susceptibility of trees to attack by southwestern pine tip moth. It is important to thin trees during the fall or winter when Ips beetles are less active. Maintaining healthy trees is also recommended since Dioryctria spp. are attracted to trees under stress due to drought, overwatering, soil compaction, root injury, pruning, or mechanical injuries. Practices that injure bark should be avoided during adult flights in July or August.
Predators and parasitoids can be effective at suppressing populations of these pests. Predators include mites, ants, spiders, wireworms, lizards, birds, and mice. Mites feed on eggs, while ants, spiders, and lizards attack exposed larvae after they leave shoots. Birds can open shoots to feed on larvae, and mice feed on larvae and pupae when they dig up cocoons at the base of trees. Wireworms feed on overwintering pupae.
Parasitic wasps in the genus Trichogramma (family: Trichogrammatidae) develop within moth eggs. Other wasp genera in the families Braconidae and Ichneumonidae can attack larvae or pupae. Geron spp. (family: Bombylidae) are parasitoid flies that can also attack moth larvae and pupae.
In small, isolated plantings, shoots infested with larvae can be clipped and destroyed to reduce populations of the southwestern pine tip moth. However, this will not prevent damage in the current year or prevent moth invasions the following spring.
Insecticides can be effective against these pests. However, timing of the insecticide application is important for effective control and depends on the species’ life history. For example, insecticidal applications for the southwestern pine tip moth are most effective for most pines when applied in late April through early May as new shoots are elongating and the needles are more than 1.3 cm (½ inch) long. For the Zimmerman pine moth, insecticides are most effective when they target larvae before they enter the bark. The best time to treat is in the spring when overwintered caterpillars emerge from their hibernacula and resume feeding. Another option is to apply insecticides during egg laying and egg hatch, which occur over several weeks in late summer.
CSFS. 2022. Pinon Pitch Mass Borer. Colorado State University – Colorado State Forest Service. Available https://csfs.colostate.edu/wp-content/uploads/2022/04/PinonPests_Pitch-Mass-Borer_CSFS_2022.pdf
Driesche, R. et al. (n.d.). Southwestern pine tip moth. Forestpests.org. Available https://www.forestpests.org/vd/415.html#:~:text=The%20southwestern%20pine%20tip%20moth,eggs%20as%20new%20needles%20emerge.
Jacobi, W., and W. Cranshaw. 2014. Pinyon Pine Diseases and Insects. Colorado State University – Extension. Available https://extension.colostate.edu/topic-areas/yard-garden/pinyon-pine-diseases-and-insects-2-948/
Jennings, D., and R. Stevenson. 1982. Southwestern Pine Tip Moth. United States Department of Agriculture – Forest Service. Available https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev2_043091.pdf
USDA. 2011. Pitch Moths. United States Department of Agriculture – Forest Service. Available https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5341333.pdf
USU. (n.d.). Pine Tip Moths. Utah State University – Extension. Available https://extension.usu.edu/pests/ipm/ornamental-pest-guide/arthopods/moths/pine-tip-moths