Prodiplosis morrisi, new species

Adults of a new species of Prodiplosis were reared from larvae found in leaf curl galls on Populus deltoides by R. C. Morris of the Southern Forest Experiment Station in Stoneville, Miss. In the spring the larvae cause a curling of the edges of young, growing leaves of cottonwood to form a green, elongated, roughly cylindrical cell, the interior of which is covered with a mucous substance. The many larvae in each cell drop to the ground to pupate at about the time the leaves are fully grown and leave the damaged leaves behind. The leaves usually are not completely killed; only the affected edges turn brown, and the midrib areas and apex remain green. Larvae in leaf galls were found at several localities in Stoneville (June 17, 1965) and in Beaumont, Texas (May 27, 1965). Six adult males were reared from a Stoneville collection on June 27, 1965. Also, late in July 1965 Morris found the typical damage on cottonwood leaves in Washington, D. C, though the midge larvae were no longer in the leaves.

Felt (1940) reported apparently this same gall, "marginal, greenish or purplish leaf rolls or folds" in Populus sp., as being formed by Cecidomyia sp. Kieffer (1909) described larvae causing a similar gall on P. tremula L. in Europe as Contarinia tremulae; however, his short description of the larva does not fit that of the new species.

Material Examined.—Holotype: Male; "Stoneville, Miss.: reared 6/28/1965; R. C. Morris; Hopkins 51521; slide 6. USNM Type no. 68761." Paratypes (all with same date and locality as above) : 5 $ on slide numbers 1-5, 1 pupa (9), 3 pupal exuviae and 14 larvae. Other material: several prefinal-instar larvae from Beaumont, Texas; 5/27/1965; R. C. Morris. All specimens deposited in U. S. National Museum collection.

The poplar leafcurl midge, Prodiplosis morrisi Gagné, is a native North American cecidomyiid fly that lays its eggs on developing cottonwood terminals. The larvae feed on surfaces of expanding leaves, causing them to curl into elongated, largely cylindrical shapes. Leaves may stay green with only curled edges turning brown, or leaf may be killed.

Cecidomyia sp.

Populus

Marginal leaf rolls or folds, greenish or purple

Prodiplosis morrisi
[page 67]

This gall midge induces rose-pink to yellow-green roll galls along the leaf margins of aspens.

Range: from the East Coast to Kansas and Texas. central Sierra Nevada in California

Prodiplosis morrisi Gagne

A little known leaf roll midge, Prodiplosis morrisi Gagne, is an important pest of Populus species in North America, especially in hybrid poplar plantations and nurseries in southern Canada and in P deltoides in the southern United States. Its larvae feed in the tightly rolled blade tissues of leaves newly emerged from terminal tips of young trees. The leaf veins and tissues are damaged and the leaf does not unroll and develop normally. Lightly damaged leaves are stunted and have crinkled, distorted margins. With heavy damage, they turn black and drop off the tree. Each midge generation affects 4 or 5 leaves and 5 generations can occur in southern Ontario between June and September.

Subsequent studies showed the margins of new emerging leaves are naturally rolled laterally and inward to the mid-rib on their upper surface. A viscuous yellowish "balsam" fluid surrounding the terminal bud and new tiny leaves is naturally present in Populus sp. This material fills the leaf tissue rolls and the feeding larvae are surrounded by it. Rather than causing the leaves to roll, the midge larvae prevent the normal unrolling of the leaf blade and its growth into a flat leaf.

The first larval collections of P morrisi were made near Beaumont, Texas in May 1965 and Stoneville MS in June 1965. The author found typical foliar damage near DC in July 1965. Prior to 1977, the midge was found at Phillipsburg, PA in 1973 and it was reported in southern Ontario in 1973-6.

A survey of hybrid poplar plantings in June, August, and September, 1977 verified the presence of P morrisi throughout southern Ontario. It was found near Wichita KS in P deltoides in 1977 and in NY in 1979. It was found in hybrid poplars in northern MI in August 1979 and it probably occurs throughout the range of P deltoides. It, or a similar species, was found in P tremuloides in eastern Ontario in 1978-9. More study is needed to determine the complete range of this native insect of poplars. It has not been found in P balsamifera, or in P alba, or P alba x hybrids in Ontario.

[Morris provides detailed information about methods in rearing experiments and other life history details]

Prodiplosis morrisi Gagne

Hosts: Populus deltoides

Biology. Larvae curl newly developing leaves of Populus deltoides and Populus tremuloides and can be an important pest in hybrid poplar nurseries in southern Canada and of cottonwood in the southern United States. The affected leaf parts turn brown. Lightly damaged ones dehisce. According to Morris (1981), five generations are possible in southern Ontario between June and September. Each generation affects 4-5 leaves. Long-run damage includes stunting of terminal leaders. Morris (1981) reported typical damage from Illinois, Ontario, and New Brunswick, south to Mississippi and west to Texas and Kansas. Larvae of P. morrisi hibernate in the duff; adults appear in Ontario around 1 June. Another Prodiplosis, a species near myricae (q.v.), has also been reared from leaf rolls of Populus sp. ("wild aspen") in southern Canada.

Range: Ontario, MS

Prodiplosis morrisi

Hosts: Populus deltoides, tremuloides, hybrid poplars

Rolled leaf or curled leaf margin

Eggs are laid in newly developing leaf buds. Larvae are gregarious within the leaf rolls of marginal curls. Full-grown larvae drop to the ground to pupate. Up to five generations occur per year in Ontario. Infested leaves become deformed and later turn brown. Severe damage can stunt terminal leaders.

Range: Eastern North American to Kansas and Texas