Diprionid Sawflies on Lodgepole and Ponderosa Pines
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Forest Insect & Disease Leaflet 179 January 2011 U.S. Department of Agriculture • Forest Service Diprionid Sawfl ies on Lodgepole and Ponderosa Pines William M. Ciesla1 and David R. Smith2 Sawfl ies of the family Diprionidae (Hymenoptera) are common defoliators of conifers throughout North America. Two genera, Neodiprion and Zadiprion, feed on the foliage of lodgepole pine, Pinus contorta, and ponderosa pine, P. ponderosa, in the West. Species of the genus Neodiprion are the most common of the North American conifer feeding sawfl ies. They can reach outbreak levels and defoliate forests of true fi r, pine, spruce, Douglas- fi r or hemlock. Larvae feed almost exclusively on old foliage of host trees. Some 47 species and 6 subspecies are known. All but seven species, the European pine sawfl y, N. sertifer (Geoffroy), and six species from China, are native to North America. Seven species are known to feed on the foliage Mature Neodiprion autumnalis larvae feeding on ponderosa pine needles. of lodgepole and ponderosa pines and can occasionally become pests in western North America. the western United States, Mexico and Guatemala. They resemble Neodiprion Zadiprion is a small genus, closely in appearance and habits. One species, related to Neodiprion, and is composed Z. townsendi (Cockerell), feeds on of fi ve pine-feeding species native to ponderosa pine. 1Forest Entomologist, Forest Health Management International, Fort Collins, CO (retired, USDA Forest Service). 2Research Entomologist, USDA Agricultural Research Service, Systematic Entomology Laboratory, National Museum of Natural History, Smithsonian Institution, Washington, DC (retired). Sawfly outbreaks can cause growth deposited on the needles. Early instar reduction and, occasionally, tree death. larvae feed only on the needle cortex, In some cases, trees weakened by leaving the midrib remaining, while defoliation are subsequently attacked mature larvae feed on the entire needle. and killed by bark beetles. Outbreaks Pellets of frass (digested foliage) can are of short duration, however, and be seen on the ground beneath heavily usually last from two to four years. defoliated trees. They tend to occur more frequently on poor sites, outwash plains or shallow, Species, Hosts and infertile soils. Forests most susceptible to sawfly outbreaks are open-grown Distribution stands or even-aged plantations located Seven species of Neodiprion and one on poor growing sites. species of Zadiprion are known to defoliate lodgepole and ponderosa pines Evidence of Infestation in western North America. One species feeds exclusively on lodgepole pine, one Typically the first indication of on both lodgepole and ponderosa pines sawfly activity is crown thinning and six feed on ponderosa pine (Table caused by larvae feeding on older 1). Of the five species of Neodiprion that foliage (Figures 1-2). During heavy feed on ponderosa pine, some, such as infestations or for species that feed N. gillettei (Rohwer), attack young trees in mid-summer, current-year’s and are a threat to plantations while foliage can also be damaged. Closer others, such as N. fulviceps (Cresson), examination may reveal the presence of prefer either pole-sized or mature trees. colonies of feeding larvae and/or eggs The lodgepole sawfly, N. burkei Middleton, is known from Montana and Wyoming where it feeds on the foliage of lodgepole pine. There is one generation per year, but a portion of each brood remains in the prepupal stage for 2-4 years. Winter is spent as prepupal larvae in cocoons in the litter. Between 1921 and Figure 1 – Defoliation of lodgepole pine by Neodiprion nanulus contortae. Figure 2 – Defoliation of ponderosa pine by Neodiprion autumnalis. 2 Table 1 – Distribution, overwintering stage and host preference for Neodiprion sawflies affecting lodgepole and ponderosa pines in western North America. Overwintering Species Distribution Type of trees attacked* stage N. autumnalis USA: Arizona, Egg Ponderosa pine: pole- California, Colorado, sized trees Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, Oregon, South Dakota, Washington. Mexico – Throughout pine growing regions N. burkei USA: Montana, Prepupal larva in Lodgepole pine: mature Wyoming. cocoon trees N. fulviceps USA: Arizona, Prepupal larva in Ponderosa pine: mature California, Nevada, cocoon trees Wyoming. Mexico: Chiapas, Hidalgo, Veracruz. N. gillettei USA: Arizona, Egg Ponderosa pine: Colorado. small trees, 3 ft tall or Mexico: Chihuahua, branches of older trees Guerrero, Michoacán. that touch the ground N. mundus Canada: British Egg Ponderosa pine: all Columbia. ages and sizes USA: Idaho, Oregon. N. nanulus Canada: Alberta. Egg Lodgepole and contortae USA: Idaho. ponderosa pines: pole- Montana, Oregon. sized to mature trees N. ventralis USA: Arizona, No data Ponderosa pine: pole- Colorado, Nebraska, available sized trees North Dakota, Wyoming. *Mexican pine hosts are not included 1925, this sawfly, in combination with a and caused severe damage on another needle tier moth, Argyrotaenia tabulana 20,000 acres. Freeman (Lepidoptera: Tortricidae), defoliated 80,000 acres in the upper Neodiprion nanulus contortae Ross Madison River Basin in Wyoming is a western subspecies of the red pine and Montana. The sawflies fed on the sawfly, N. nanulus nanulus Schedl. It older foliage and the needle tier on occurs in Idaho, Montana, Oregon and new foliage. The two defoliators killed adjoining portions of Alberta, Canada. almost all of the trees on 12,000 acres Larvae feed on both lodgepole and 3 ponderosa pines. Winter is passed in western Kansas and New Mexico. It the egg stage. Eggs hatch in early to also occurs throughout the pine forests mid-June and larvae feed until early of Mexico, where it feeds on several July, then drop into the litter and Mexican pines. Adults emerge in fall, upper layers of soil, spin cocoons and hence the species name autumnalis, exist as prepupal larvae until early and deposit eggs, which overwinter. September when pupation occurs. Adult Larvae hatch the following spring emergence, mating and egg deposition and can feed until late summer, after occurs from mid-September to mid- which they pupate. During the early October. Females deposit an average of 1990’s outbreaks occurred in western 9.49 eggs in needles of lodgepole pine South Dakota (3,500 acres) and eastern and 19.15 eggs per needle on ponderosa Wyoming (84,000 acres). Outbreaks pine. have also occurred in the ponderosa pine-grassland transition zones in east Outbreaks have been reported from central Colorado and north-central several locations. In Klamath County, Arizona. Widely-spaced trees growing Oregon, outbreaks occurred from on dry sites with poor soils tend to be 1941-45 and 1952-53. Some trees most heavily damaged. In addition to were killed outright by the defoliation older needles being almost completely and others succumbed to attack by consumed, current-year needles on other insects. Most trees recovered many trees can be clipped by mature but suffered reduced growth. During larvae. 1959-61, an outbreak was reported near Zortman, Montana. This outbreak Neodiprion fulviceps is known from covered 11,000 acres before declining Arizona, California, Nevada and due to a nucleopolyhedrosis virus. In Wyoming. It is fairly widespread but 1973 a localized outbreak occurred on not as common as N. autumnalis. It portions of the Kootenai National Forest overwinters in cocoons as prepupal in northwestern Montana. Another larvae and pupae in the soil. Adults outbreak occurred on several national emerge in mid-April to late May and forests in eastern Oregon in 1978 and lay eggs in the needles of ponderosa caused over 3,000 acres of aerially pine. Larvae hatch from mid-late June visible defoliation of lodgepole pine. and feed for about four weeks before In 2010, a localized population was dropping to the soil to form cocoons. detected on lodgepole pine near Gallatin An outbreak of N. fulviceps occurred Gateway, Montana. in the vicinity of Flagstaff, Arizona between 1982 and 1985. Neodiprion autumnalis Smith and N. fulviceps are two closely related Neodiprion gillettei occurs in Arizona, species and are separated primarily Colorado and Mexico, where it has been on differences in their life cycles. collected in the states of Chihuahua, N. autumnalis is the most wide- Guerrero and Michoacán. This sawfly ranging of the pine sawflies that feed is unique in that it feeds on young trees on ponderosa pine. This species is (<2 feet tall) or branches of trees that known to occur throughout the western touch the ground. Adults emerge, mate United States east to western South and lay eggs on pine needles in fall. Dakota, western Nebraska, Colorado, Eggs hatch in spring and larvae feed 4 for about four weeks between April and defoliation but an outbreak occurred May. Between 1967 and 1968 more than from 1908 to 1910 in northwestern 810 acres of ponderosa pine seedlings Nebraska and southwestern South were infested on the Sitgreaves National Dakota. Forest south of Winslow, Arizona, with heavy damage on about 10% of the area. Life Stages Neodiprion mundus Rohwer occurs Adults are small wasps with stout, from the southern interior of British thick-waisted bodies and most species Columbia south to Oregon and Idaho. are similar in appearance. In most In British Columbia, localized outbreaks cases, identification to species is based have been recorded in the Deadman on females and must be made by a River area from 1946 to 1951 and along taxonomist. Females are larger than the northern arm of Okanagan Lake in males. Females of the genus Neodiprion 1964. This insect has one generation range from 8.5 to 10 mm (0.3 – 0.4 per year and overwinters in the egg inches) long. Most species have two stage. Larvae are present from late pairs of clear wings, light red to red- May to June. It is a common but rarely brown heads, serrate reddish-brown destructive defoliator to black antennae and light brown to yellowish-green abdomens (Figure Neodiprion ventralis Ross is a little 3).