Rhopalomyia pomum

Rhopalomyia hirtipomum

Rhopalomyia calvipomum

Rhopalomyia tubulus

Rhopalomyia hirtibulla

Rhopalomyia tumidibulla

Rhopalomyia ampullaria

Rhopalomyia brevibulla

Rhopalomyia gossypina

Rhopalomyia culmata

Rhopalomyia rugosa

Rhopalomyia lignea

Rhopalomyia lignitubus

Rhopalomyia cramboides

Rhopalomyia anthoides

Rhopalomyia florella

Rhopalomyia conica

Rhopalomyia mammilla

Rhopalomyia obovata

Rhopalomyia nucula

Rhopalomyia medusa

Rhopalomyia medusirrasa

Rhopalomyia hirticaulis

Rhopalomyia tumidicaulis

Rhopalomyia alticola

Rhopalomyia betheliana

Rhopalomyia clinata

Rhopalomyia coloradella

Rhopalomyia floccosa

Rhopalomyia subhumilis

It is very close to R. hirtipomum and R. calvipomum, which form the same general type of gall. The external anatomy of R. hirtipomum appears identical with R. pomum, but it's gall has a very fuzzy surface and is always monothalamous. 

The monothalamous galls were the first to show midge emergence. Under field conditions emergence occurred as early as May 7, 1969 at Site 1 when a few fresh pupal exuviae were found. On May 28th some pupae were present at this site indicating that emergence was still in progress, but it was completed sometime prior to June 13th. Examination of galls at Site 3 at a higher elevation showed that adult emergence had commenced no more than a few days prior to May 19, 1969. 

This persistent leaf series gall is either monothalamous or polythalamous. This mature form varies from globose to distinctly irregularly lobed. The surface of the monothalamous galls is uniform while that of the polythalamous galls (Fig. 3) has both deep and shallow fissures giving the gall a lobed appearance. The color ranges from reddish to a common pattern of mottled reddish and greenish to completely green. The surface is covered with short trichomes. Often monothalamous and polythalamous galls are present on the same plant (Table 5) with the latter usually predominatory. A total of 1185 galls (1166 polythalamous and 19 monothalamous) occured on a sampled plant at Site 2. 

Under the surface layer the gall consists of a spongy mass of interwoven fibers. Within this fibrous mass near the base of the gall are the sclerenchymatous larval capsules. A single fiber extends from the upper portion of each capsule to a small brown spot on the gall surface. 

One hundred fifty galls had a range of 13-45 mm (avg. 26) for their greatest diameter across the gall from it's base. An opposing diameter at the widest point perpendicular to this diameter ranged from 12-40 mm. 

Developing gall appear as small irregular swellings on either surface of a persistent leaf (Fig. 5). They have a dense covering of trichomes which gives them a gray color except for small brown spots on the surface which are free of trichomes. 

Rhopalomyia hirtipomum appears to be anatomically identical to R. pomum but is responsible for a slightly different gall. That of hirtipomum is densely covered with long trichomes, whereas that of R. pomum has short, prostrate, sparse trichomes on the surface. In addition, galls of the former are always monothalamous. 

This monothalamous gall (Fig. 9) is globose and quite similar to the monothalamous gall of R. pomum. However, the gall surface is densely clothed with long trichomes, giving it a fuzzy appearance. The gall is generally solitary on either the upper or lower leaf surface, but can occasionally be found in confluent clumps (Fig. 10). Fifty-nine mature galls were measured: the diameter extending from the gall base ranged from 8-15 mm (avg. 12) and the diameter perpendicular to this ranged from 8-13 mm (avg. 11).

Developing galls were first found on October 23, 1969 at Site 1 on A. t. wyomingensis. They appeared as fuzzy swellings with diameters of 1-3 mm on a persistent leaf surface. The long, dense trichomes were white, while the surface of the gall was reddish. Galls had the same appearance on A. t. vaseyana f. xericensis when found at Site 27 on December 29, 1969. At both sites this appearance persisted until March, when growth resumed. As the gall grew, their surface coloration gradually changed to grey. Maximum size of the gall was found to coincide with the presence of pupae and with new stem growth of approximately 2.5 cm in length. Shedding of the galls occured in July and August, at the same time as those of R. pomum.  


This species is most similar to R. pomum and R. hirtipomum. All three species form the same general type of gall, but that of R. calvipomum is naked. 

The mature gall (Figure 8) is globose to irregularly elongate and is similar to that of R. pomum in shape and by having small brown spots on the surface. It differs by being firmer and having a smooth surface that lacks trichomes. 

One hundred fifty mature galls were measured: the diameter extending from the gall base ranged from 9-26 mm (avg. 15) and the diameter of the greatest width perpendicular to the previous measurement ranged from 8-20 mm (avg. 13). 

Developing galls were evident on March 23, 1970 at Site 21. They appeared as a reddish or violet-colored swelling of a persistent leaf. Galls fall from the plant in July and August, as do those of R. pomum. 

The mature gall is tube-shaped (Fig. 11). The surface is dark reddish and covered with the same white trichomes as on the normal leaf surface. The gall has a single larval chamber at the base, is hollow in the center and has a thin septum near the apex. The hollow portion is utilized by the pupa to facilitate escape, with the pupal exuvium remaining at the ruptured apical septum. 
In appearance the developing gall differs only in size from that of the mature gall. 

This small monothalamous gall (Fig. 12) occurs singly or in small to large confluent groups. The galls are densely clothed with long trichomes giving them a white fuzzy appearance. The mature gall is approximately 1 mm in diameter and of equal height. Emergence of the adult from a central larval chamber results in a small circular hole (Fig. 23) at the top of the gall. 

Developing gall were first observed on July 19, 1968 at Site 15. They are similar in appearance to the mature galls. Growth was completed between that date and the end of March of the following year. Old galls remain on the plant until the persistent leaf series is shed. 

Adults emerged in the laboratory on March 25-26 from galls that had been collected March 18, 1970. In the previous year's rearing, they emerged on April 24-25 from galls collected April 22, 1969. 
 
This monothalamous gall, when mature, consists of a swelling that is apparent on both surfaces of a persistent leaf (Fig. 15). A sclerenchymatous larval capsule is located centrally within the leaf swelling. Two mature galls measured 3 mm. in depth, 3 mm across the leaf width and 4 mm along the leaf length. 

This species has two generations per year. The summer generation develops in galls principally on ephemeral leaves while the overwintering generation develops in galls on flower buds.

The flower bud gall of the overwintering generation is not readily visible. The affected buds remain closed during bloom and the gall can be found only be forcing open the involucral bracts. An elongate sclerenchymatous larval capsule with a dense covering of long white trichomes replaces the flower. During the period of full bloom the capsule is green but after bloom the gall becomes translucent and colored much like that of the dry involucral bracts. By the summer following adult emergence, all galls have dropped from the plant. The few mature galls measured were approximately 2 mm in length and 1 mm in width. [Description about biology and seasonal occurrence of the summer generation gall is given but no description of the gall itself is provided. It is shown in Figure 16 later in the paper however.]

This species forms galls similar to those of R. hirtibulla except that they are not covered by long trichomes. 

This small monothalamous gall (Fig. 13) is similar in size and structure to that of R. hirtibulla. The grayish surface of the mature gall is clothed with trichomes the same as on the leaf. The galls occur singly or in large clusters both on the persistent leaf series and stems of the previous year's growth. Adult emergence holes are similar to those of R. hirtibulla (Fig. 12). The galls have been found on only one small plant at the type locality. 

This gall is a composite growths of the branch tips and buds (Fig. 19). At maturity it consists of 2-4 short, malformed, developing stems that are grouped in a globose mass of white trichomes from which green leaves protrude. The surface of these stems is densely clothed with white trichomes which are longer than the linear leaves arising from these stems. Hidden by the dense trichome mass, sclerenchymatous larval capsules are on the axis of the stems. These capsules are elongate cylinders with a rounded apex and a thin hard wall. The galls are generally found concentrated on one branch. 

Fifty mature galls ranged in height from 8-15 mm (avg. 11.68). Their width ranged from 8-16 mm (avg. 12.88). Five of the larval capsules were approximately 2 mm in height and 1 mm in width. 

Early development of this gall was noted on June 5, 1969 at Site 24. The immature gall is recognized as a mass of white trichomes subtended by a whorl of developing ephemeral leaves at the tip of a developing stem. The galls increase in size during the summer and reach what appears to be maximum size in late August when the ephemeral leaves begin to dry. The galls remained unchanged in appearance after adult emergence and throughout the winter. The following spring the trichomes on the gall surface become drab. The old galls persist up to two years and perhaps longer in sheltered parts of the plant. 

Pupal exuvia were found on a gall on May 27, 1969 at Site 3. Adults were reared April 21-26, 1972 from galls collected April 18 at Site 15. 

This monothalamous gall appears to be associated with one of the first ephemeral leaves that develop in the bud. The mature gall consists of a long, thin erect stalk with an enlarged apex made up of the fused lobes of the leaf tip (Fig. 18) surrounding a sclerenchymatous larval capsule. Some galls have a whorl of spatulate leaves at the base of the stalk. Two galls that were measured had stalks 10 mm long and the enlarged apical portions 5 mm long by 2 mm wide. 

Two adults emerged within 2 weeks after galls were collected May 9, 1989 at Site 6.

This monothalamous gall develops from the upper surface of a persistent leaf. The coloration and pubescence of the gall surface is similar to that of the unaffected leaf. At maturity it is prune-shaped. Internally, a central cavity is lined with sclerenchyma. Only two galls, both occurring on the same leaf, were found during this study. They were 4 mm in height and 2 and 3 mm respectively in diameter. 

Adults emerged from galls in the laboratory within two weeks of their collection on April 22, 1968 at Site 14. 

This bud gall (Fig. 21) is a confluent mass of swollen leaf rudiments which are green and densely covered with trichomes. Each leaf rudiment tapers from a broad base to a blunt apex, becomes woody at maturity, has a single larval chamber at the base, is hollow in the center, and has a thin septum at the apex that bears a mass of long trichomes. The hollow portion is utilized by the pupa to facilitate escape. The pupal exuvium remains at the ruptured septum. The old galls persist on the plant indefinitely. Three mature galls had a respective length of 8, 6, and 8 mm with a basal width of 4, 4, and 6 mm. 

The formation of these galls marked the end of any normal growth from the buds. However, these galls were never abundant enough to cause any significant damage to sagebrush plants. 

Immature larvae were found at Site 27 on March 8, 1970 coinciding with the first sign of gall development. Pupae were found on May 14, 1969 at Site 1 on A. t. tridentata and at Site 4 on May 29, 1969 on A. t. vaseyana. Adults emerged May 19, 1969 from galls collected on May 14 at Site 1. A pupal exuvium was found at the apex of each gall's hollow portion. 

This bud gall (Fig. 23) develops in the spring when plant growth begins. It is green and appears to be made up of a series of fused leaves that form a woody, hollow structure that is open apically. The inner surface of the gall is densely clothed with long trichomes while the outer surface is covered with shorter trichomes. The base of the gall contains a single larval chamber. Some developing galls (Fig. 24) are short and dark reddish. After adults emergence the woody gall dries and persists on the plant for a year or longer. 

Eighteen mature galls from A. t. vaseyana and A. t. wyomingensis ranged in length from 10-19 mm (avg. 12). The basal diameter ranged from 4-6 mm (avg. 4). Three galls from A. t. tridentata had had respective lengths of 15, 17, and 25 mm and all with a basal diameter of 3 mm. 


This gall develops from the buds forming on new stem growth. It has a broad base made up of several whorls of fused and stunted leaves subtended by a pair of normal ephemeral leaves (Fig. 25). The outermost leaves are as wide as long while the inner leaves are oblong. The gall is green and normally covered with trichomes. The sclerenchymatous larval capsules in the mature gall are located at the bases of the innermost leaves at the stem apex. These galls are commonly found in clusters on a single branch. 

Fifty mature galls had a width (diameter at widest point) ranging from 5-12 mm (avg. 9) and a height (base of gall to leaf apices) ranging from 5-12 mm (avg. 8). There are 1-8 sclerenchymatous capsules per gall. 

The developing galls, containing early instar larvae, differ from mature galls only in size. The gall usually attains maximum size by winter although some growth may occur in the following spring. After midge emergence the galls begin to dry and within a year the leaves are lost but the galls persist indefinitely as dark, woody bodies on branch tips of the plants. 

The bud galls of R. anthoides superficially resemble those of R. florella. 

Immature larvae were found June 10, 1968 at Site 15 coinciding with the first sign of gall development. The larvae appeared to have reached maturity by late November or early December and completely filled their individual sclerenchymatous capsules. 

This bud gall has a seasonal occurrence similar to that of R. cramboides. In appearance it differs by being longer and less rounded and in structure by having the leaves composing the rosette more linear. In addition, the long outer leaves surround the shorter leaves of the gall base. All leaves of this gall on A. t. wyomingensis have a proliferation of long trichomes especially at their base (Fig. 27) while the leaves on A. t. vaseyana gall have trichome proliferation only on the inner leaves. 

Eighty-four mature galls from A. t. wyomingensis at Sites 15 and 16 had a basal diameter ranging from 4-15 mm (avg. 8) and a height (length of outer leaves) ranging from 5-17 mm (avg. 11). Fifty-nine of these galls had 1-49 sclerenchymatous larval capsules (avg. 4). 

Developing galls differ from mature galls mainly in size. Maximum size of the gall appears to be attained by winter. Following adult emergence in spring the galls dry out and darken in color but persist on the plant a year or longer. 

Adults emerged on March 25 and 26, 1970 from galls collected on March 18 at Site 15. 

This rosette bud gall (Fig. 29) is similar to that of R. anthoides in general structure and in plant parts affected it appears identical. However, it differs by having the inner leaves similar in length to the leaves of the outer whorls. In addition, galls on both A. t. vaseyana (Fig. 29) and A. t. wyomingensis have a proliferation of long trichomes on all leaves. In size the gall of R. florella is about the same as the smaller galls of R. anthoides. 

This bud gall is monothalamous. The mature gall is green and covered with trichomes. The larval capsule has a yellowish translucent sclerenchymatous surface. On A. t. tridentata the prominent sclerenchymatous larval capsule of the mature gall (Fig. 30) is surrounded by a whorl of basally fused leaf vestiges around which are several whorls of linear or spatulate leaves that gradually increase in length outwardly. The gall is irregularly rosette in form. On both A. t. vaseyana and A. t. wyomingensis the mature gall (Fig. 31) is more normally rosette. The sclerenchymatous larval capsule is surrounded by several whorls of equally long, ovate leaves. 

Thirty-one mature galls collected at Site 1 and 2 on A. t. tridentata had a diameter (measured at base including inner whorl of leaves) ranging from 3-6 mm (avg. 4). The sclerenchymatous capsules of these galls had a length range of of 3-4 mm (avg. 3.2) and the width or diameter of each was approximately 1 mm. The diameter (measured across the apices of the outer leaves) of 26 mature galls collected at Sites 15 and 21 from A. t. wyomingensis ranged from 8-21 mm (avg. 9.41). 

Developing galls occur with the initiation of spring plant growth. On A. t. wyomingensis the developing gall was first found seasonally on March 23, 1970 at Site 12 and on A. t. vaseyana the following day at Site 27. The galls dry shortly after midge emergence the following spring and persist on the plant into at least late summer. Galls from which emergence has occured are readily recognized by the protruding larval capsule that is broken apically. 

Adults emerged September 10-17, 1968 from galls collected on September 9 at Site 14. On the collection date the host plants were in early bloom. 

This polythalamous rosette gall (Fig. 32) grows from a bud on the current year's stem and is subtended prior to maturity by two or more ephemeral leaves. It is composed of several whorls of mostly equal, linear to acicular leaves surrounding two to four sclerenchymatous larval capsules. 

The basal diameter of one measured gall was 6 mm. Its outer leaves were up to 10 mm in length and the other leaves approximately 5 mm in length.  

Immature larvae were found June 13, 1969 at Site 1 on both A. t. tridentata and A. t. wyomingensis, coinciding with the first sign of gall development. By late fall the larva reaches maturity. They are a darker orange color than larvae found earlier and they completely fill the sclerenchymatous capsule in the center of the gall. Overwintering occurs at this state of development. Adults were emerging by March 24, 1969 at Site 1, whereas in 1970 they emerged before March 20 at this site and before March 19 at Site 24. Emergence was in progress as late as May 18, 1968 at Site 8. 

This ovoid bud gall has vestiges of spatulate leaves (Fig. 33). Its smooth, green surface is densely covered with trichomes. Maturity is reached in the fall after which degeneration begins. The gall surface dries and hardens, becoming shiny yellow-brown and losing its trichomes and the leaf vestiges. By late fall the tissue beneath the surface layer dries to a hard black mass which surrounds the 1-4 sclerenchymatous larval capsules containing the overwintering larvae. These dry galls persist on either vegetative or flower stems into the following spring until shortly after the midges emerge. 

Seventy-eight mature galls from the three subspecies of A. tridentata collected from Sites 1, 15, 21 and 27 ranged in diameter from 5-10 mm (avg. 7) and in height from 6-11 mm (avg. 8). No size differences of the galls could be attributed to host plant or location. Ten immature galls collected from A. t. tridentata at Site 1 on June 13, 1969 had a diameter ranging from 204 mm [presumably a typo, most likely meant "2-4"] (avg. 3). 

The white or gray polythalamous gall (Fig. 34) appears to be a concentration of individual, ovoid galls (Fig. 35) that form a globuliferous mass around a stem. The gall is a firm mass of plant tissue with centrally located larval chambers. The surface is densely clothed with long trichomes giving it a fuzzy appearance. 

Sixty-three mature galls collected from A. t. tridentata and A. t. wyomingensis at Sites 1, 21, and 24 ranged in width (diameter perpendicular to stem) from 30-15 mm (avg. 9) and in height (diameter parallel to stem) from 3-10 mm (avg. 6). These galls had 1-11 (avg. 5) larval chambers. 

Galls develop from summer to the following spring with most noticeable growth occurring before winter. The first sign of the developing gall was in early June when immature larvae were found. At this time ephemeral leaves were near full growth, the persistent leaves were nearly dry, and the gall appeared as a small white globose structure at a node. Ten of these developing galls collected on June 18, 1969 at Site 1 ranged in width from 1.5 to 2.5 mm (avg. 1.9) Galls begin to dry and decompose after midge emergence. However, old gray colored galls were observed persisting on plants for at least a year. 

Rhopalomyia medusa and R. medusirrasa are anatomically indistinguishable as adults, larvae and pupae. However, their galls are sufficiently different to warrant recognition of these species. Although the galls are the same general type, that of R. medusa is naked, whereas that of R. medusirrasa is thickly covered with long trichomes.

The mature gall (Fig. 36) consists of a larval chamber (Fig. 37) enclosing in a globular mass of reddish, green, or reddish and green filaments that lack trichomes. The filaments are thickened basally and become thinner, curly and branched distally. Frequently, galls form on several adjacent stem and leaf nodes and encompass large areas of the stem (Fig. 38). 

One hundred mature galls from A. t. tridentata, A. t. vaseyana and A. t. wyomingensis collected at Sites 1, 7, 21 and 24 had a diameter (the fibrous mass measured perpendicular to stem) ranging from 8-29 mm (avg. 13.3). Seventy-five of these galls contained 1-3 larval chambers (avg. 1.2). Larger galls were usually observed on more vigorous roadside plants on A. t. tridentata. 

The first sign of galls was during early September 1968 on both A. t. tridentata and A. t. wyomingensis. The developing galls were observed on the other host subspecies later in the fall. The galls first appear as groups of tiny leaflike structures growing from the nodes (Fig. 39). Gall development continues during the fall, is arrested during the winter, and continues in the spring with maximum size of the galls reached about the time pupae are present. Within a month after adult emergence the galls become dry and brown. They persist on the host plants for 2-12 months or longer. Developing galls were often found on flower stems but did not reach maturity because these stems died out following bloom in fall. 

Adults, larvae, and pupae of this species are anatomically indistinguishable from R. medusa. Both form the same type of gall but that of R. medusirrasa is densely covered with long trichomes, whereas that of R. medusa is naked. 

This gall (Fig. 40) resembles that of R. medusa but differs in that all radiating filaments are densely clothed with long trichomes. These trichomes generally mask the reddish and green colors of the filaments and give the gall a white or gray appearance.

Twenty-four mature galls from Sites 6 and 25 had a diameter (measured perpendicular to stem) ranging from 12-25 mm (avg. 17). Thirty-one galls that were collected April 14, 1969 at Site 6 prior to ephemeral leaf development had a diameter ranging from 6-16 mm (avg. 10) and contained 1-4 larvae (avg. 2). The first sign of gall development was in early October with the appearance of small clumps of leaflike structures covered with trichomes at the nodes. The galls grow during the fall and again in the spring until about the time pupae are present. After adult emergence the galls dried but retained their gray appearance and persisted on the plants as for those of R. medusa. 

This species and R. tumidicaulis are the only ones responsible for stem galls on A. tridentata. 

Immature larvae were found June 5, 1969 at Site 24, coinciding with the first sign of gall development. Adults emerged in the field on July 23, 1969 at Site 23, and at Site 24 sometime prior to August 8, 1969. 

The mature gall is a slight swelling of the vegetative stem and is covered by long white trichomes (Fig. 41). Its sclerenchymatous larval capsules are found between the woody tissues and the outer layers of stem tissue. The galled stem may be slightly bent or, if larvae are near the apex of the gall, it may be stunted. 

Forty mature galls from Sites 23 and 24 were measured with the length of the stem surface covered by long trichomes ranging from 4-19 mm (avg. 9). The length of the trichomes ranged from approximately 1 to 2 mm. The galls contained from 1-7 larval chambers (avg. 2). 

Developing galls were first observed in early June and found to differ from mature galls only in size. Galls were mature in mid-July when the larvae and pupae were well encapsulated within the stem and normal ephemeral leaves were mature. The old galls persisted on the plant for a year or more. 

This species and R. hirticaulis form the only stem galls known on A. tridentata. 

Adults emerged September 19-25, 1968 from galls collected on September 4 with pupae present. 

This polythalamous gall (Fig. 42) reaches maturity in the early fall just prior to bloom. It forms a swelling on a vegetative stem that becomes stunted, has numerous nodes and has small malformed leaves. Interspersed among the wood fibers of the inner stem are the sclerenchymatous larval capsules. 

The length of nine of these stunted stems ranged from 5-23 mm (avg. 15). Three galls contained six, seven and eight larval capsules respectively.  

Only a gall remains of the type series in the USNM. Cockerell subsequently collected more adults which were described by Felt (1915b). 

The gall is a spherical mass of long trichomes, about 15 mm in diameter. It consists of an aggregate of several capsules each of which encloses a larva. From the figure in Felt (1940), the gall appears to be either a node or bud gall. 

In the original description (Cockerell, 1890), the host of R. alticola was given as "a composite... a Chrysopsis or Solidago." Cockerell (1909) subsequently recorded the host as "Artemisia canadensis [now considered a subspecies of Artemisia campestris]." Felt (1917) later listed "Artemisia forwoodii (? canadensis)" and, questionably, A. caudata as hosts. Baker (1895) reported a similar gall on "A. dracunculoides."

This is a monothalamous, pyriform, approximately 34 mm long by 2 mm in basal diameter. It is covered with trichomes and occurs on the flower buds (cf. Fig. 335, Felt 1940).

Lectotype male, here designated, Denver, Colorado, emerged III-1909, "Artemisia frigida", in USNM. 

Diarthronomyia californica Felt 1912:752, Junior secondary homonym of Rhopalomyia californica Felt 1908. 
Rhopalomyia clinata Gagne 1975:483, new name for californica (Felt 1912a)

Lectotype, male, here designated, Claremont, Los Angeles Co., California, C. F. Stahl, emerged III-12-1912, "Artemisia californica"

This is small, brown, monothalamous, subconical, thin walled, naked, and protrudes at an oblique angle from the surface of the leaf. The gall is figured in Felt (1940). 

Cockerell (1904) described it as a deformed flower head, about 10 mm long by 5. 6 mm broad and covered by the greatly enlarged involucral bracts, which are outwardly smooth, reddish to yellowish, and inwardly covered with white trichomes. The host was given only as "Artemisia sp." Inasmuch as Rhopalomyia sp. appear to have narrow host preferences, future identification of R. coloradella should be difficult. 

Syntypes, 2 females, from galls on "Artemisia californica"...

This is large and woolly. It is figured in Felt (1940), and is known from Marin and Santa Barbara Counties, California. 



The gall is a polythalamous nodule on underground parts of the herbaceous Artemisia ludoviciana (Nuttall.). Ranasinghe (1978) reported on the bionomics of R. subhumilis in Utah. 

Biology and taxonomy of the Rhopalomyia Gall Midges (Diptera: Cecidomyiidae) of Artemisia tridentata Nuttall (Compositae) in Idaho