Lesser Peachtree Borer, Synanthedon pictipes
Order: Lepidoptera
Family: Sesiidae
Description
Adult males and females are similar in appearance and resemble wasps, although males are slenderer and have finely tufted antennae. Male moths also have narrow yellow bands on the second and fourth abdominal segments. These moths have clear wings and slender, dark blue bodies with a metallic sheen and pale yellow markings. They are roughly 1.3 cm (1/2 inch) long and have a wingspan of 18-25 mm (7/10-1 inch). The eggs are about 0.6 mm long, oval shaped, and red to brown. Mature larvae are roughly 2.5 cm (1 inch) long with light brown heads and creamy white or pinkish bodies.
Quick Facts
- The lesser peachtree borer is a native moth of North America and a pest of trees that produce stone fruits (Prunus spp.) such as peach, plum and cherry.
- This pest attacks older trees and can be found in branches, scaffold limbs, and portions of the trunk above the ground. Effective prevention is often adequate in managing this pest.
- The peachtree borer (Synanthedon exitiosa) and lesser peachtree borer are two closely related species. Although they have similar biology, there are important differences.
Lesser peachtree borer larva. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Lesser peachtree borer adult. Image credit: Carroll E. Younce, USDA Agricultural Research Service, Bugwood.org
Injury on cherry tree trunk caused by lesser peachtree borer. Image credit: Randy Cyr, Greentree, Bugwood.org
Damage on tree branch caused by lesser peachtree borer. Image credit: Carroll E. Younce, USDA Agricultural Research Service, Bugwood.org
Damage to black cherry tree caused by lesser peachtree borer attacking a pruning scar. Image credit: James Solomon, USDA Forest Service, Bugwood.org
Life history and habits
This species overwinters as partially developed larvae in galleries under tree bark. Overwintered larvae resume feeding when temperatures are suitable the following spring. Fully developed larvae pupate in cocoons covered with frass. Before moths emerge, pupae partially move out of hiding, and pupal skins are often left protruding from bark after moths emerge. Adults emerge throughout the growing season. Unlike most moth species, adults of the lesser peachtree borer are active during the day. After emerging from the host tree, female moths begin emitting sex pheromones to attract mates. After mating, females lay eggs singly in bark cracks or under bark in areas that were previously damaged by canker disease, winter injury, sun scalding, and mechanical wounds. Areas of bark with fresh gum are also attractive egg-laying sites for female moths. Females tend to avoid laying eggs in peach limbs under 1 cm (2/5 inch) in diameter, and several females can lay eggs in and around a single wound. Oviposition behaviors involve crawling into wounds and probing for cracks in which to lay eggs, which protect the eggs from exposure to predators and insecticides. It is worth noting that oviposition continues beyond fruit harvest, at which point insecticides are no longer being applied against fruit-infesting pests. On average, a single female lays 400 eggs on scaffold limbs, branches, and trunk. The eggs hatch in as little as 8 days, depending on temperature. Upon hatching, larvae burrow into bark through cracks caused by winter injury, pruning, or mechanical wounds, or on uninjured trees that have rough bark. Larvae of the lesser peachtree borer are rarely found at heights above 2.5 m (8.2 feet), and a small proportion of larvae can be found below ground with larvae of the peachtree borer. Many larvae can feed in a small area and the number of larvae can increase rapidly within a single wound. In addition to colonizing cultivated plants, the lesser peachtree borer also inhabits wooded areas.
Injury
Lesser peachtree borer infestations tend to be severe in older orchards with prior Cytospora canker infections, winter injury, or other wounds caused by pruning or machinery. Larvae are very active and tend to feed near the edges of such wounds. The gum exuded from wounds oxidizes over time, giving older wounds a darker color. Young larvae are sometimes found trapped inside freshly exuded gum. The larvae feed and develop underneath the bark, which causes girdling of the trunk or limb and can lead to the early decline of orchards. Production of injured limbs decreases, and when fruits are produced the weakened limbs may break under the weight. As the larvae feed and develop, they produce excrement (frass) that becomes trapped in gum. It is important to note that wounds exuding clear gum without particles of wood are not due to feeding of peachtree borer. Pupal skins often protrude from the exit holes produced by emerging adults at infested sites.
Monitoring
Pheromone traps are an effective tool for monitoring peachtree borer abundance. Monitoring data from traps can be used to determine the most effective time to apply insecticides. When moth flights are increasing, monitoring the number of cocoons and empty pupal cases protruding from bark near the tree base is also helpful.
Prevention
This pest is not usually problematic in orchards that are well maintained. Careless pruning, broken branches, sun scalds, water injury, and cracked limbs from scale infestations degrade the health of trees and makes them more susceptible to lesser peachtree borer attack. Practices that minimize mechanical injuries due to cultivation, mowing, and harvesting can reduce the pest density. Controlling diseases that cause rough, healed areas can reduce the availability of egg-laying sites. When damage is present, it is recommended to clean the damaged area of all rotten wood and debris before applying tree paint.
Cultural control
Hand removal of larvae is an effective option for trees near homes or residential landscapes. A knife or wire can be inserted into galleries to remove or crush larvae. However, it is important to cut bark vertically and avoid cutting more than necessary, as the additional damage to the bark may further degrade tree health.
Biological control
Laboratory experiments have shown that certain entomopathogenic nematodes, namely Steinernema spp. (Rhabditida: Steinernematidae), can infect larvae of the lesser peachtree borer. However, unlike the galleries produced by the peachtree borer which are concentrated underground and on the lower trunks of host trees, infestations of the lesser peachtree borer tend to occur in the trunk and scaffold limbs. This poses an extra challenge to the use of nematodes for biocontrol of lesser peachtree borer since they are highly susceptible to desiccation and exposure to ultraviolet light. Research is ongoing to test different formulations, application protocols, and environmental manipulation practices that enhance the degree of control achieved with entomopathogenic nematodes.
Chemical control
Foliar sprays are only effective when applied during egg hatch since larvae are protected from insecticides once they become established under bark. The use of pheromone traps will help growers estimate the timing of egg hatch. Spraying should be done after the first moths are captured in traps. Sometimes multiple sprays may be warranted for older trees with cracking and sun scalded limbs since they are more susceptible to injury.
References
Bessin, R. 2019. Lesser Peachtree Borer. University of Kentucky: College of Agriculture, Food and Environment. Available https://entomology.ca.uky.edu/ef213
BugwoodWiki. 2010. Synanthedon pictipes. BugwoodWiki. Available https://wiki.bugwood.org/Synanthedon_pictipes
Cottrell, T., D. Shapiro-Ilan, D. Horton, and R. Mizell. 2011. Laboratory Virulence and Orchard Efficacy of Entomopathogenic Nematodes Against the Lesser Peachtree Borer (Lepidoptera: Sesiidae)
Cottrell, T., T. Beckman, and D. Horton. 2011. Lesser Peachtree Borer (Lepidoptera: Sesiidae) Oviposition on Prunus Germplasm. Environmental Entomology. 40(6): 1465-1470. Available https://colostate.primo.exlibrisgroup.com/discovery/fulldisplay?docid=cdi_pubmed_primary_22217762&context=PC&vid=01COLSU_INST:01COLSU&lang=en&search_scope=MyCampus_FC_CI_PU_P&adaptor=Primo%20Central&tab=Everything&query=any,contains,lesser%20peachtree%20borer&facet=searchcreationdate,include,2000%7C,%7C2020&offset=0
Meyer, R. 1982. Biological Characteristics That Make the Lesser Peachtree Borer (Lepidoptera: Sesiidae) a Pest on Peach Trees. The Great Lakes Entomologist. 15(3): 189-192. Available https://scholar.valpo.edu/cgi/viewcontent.cgi?article=1435&context=tgle
Virginia Tech. (n.d.). Lesser Peachtree Borer, Synanthedon pictipes (Grote & Robinson. Virginia Tech. Available https://www.virginiafruit.ento.vt.edu/lptb.html