Pachypsylla venusta

Pachypsylla celtidisgemma

Pachypsylla celtidisinteneris

Pachypsylla celtidismamma

Pachypsylla pallida

Pachypsylla celtidiscucurbita

Pachypsylla celtidispubescens

Pachypsylla celtidisvesicula

Pachypsylla laevovesicula

Pachypsylla reticulovesicula

Pachypsylla celtidisasterisca

Pachypsylla rugosa

Pachypsylla venusta

Gall: Occurs at junction of leaf blade and petiole, spherical on C. laevigata, sometimes irregularly shaped and lobed on C. reticulata especially in western Texas, outer covering open above forming a cavity over the cells; polythalmic with 1-30 cells, average about 6; size from 3 mm to over 2 cm. The structure of this species and its large size permits it to be readily distinguished from the other species of Pachypsylla.  Its galls are so regularly present and abundant in Central Texas that they are practically a key feature for the hackberries of this region.  Since, however, it is not common in the northern states where most work on Pachypsylla has been carried out only incidental notes have appeared In the literature concerning its biology.

Range: Tuthill  (1943) states that P. venusta was known at that time from Iowa, Kansas, Colorado, Texas, New Mexico, Ohio, Mississippi, Tennessee, North Carolina, New Jersey, and Con-necticut.  Wells  (1914), however, stated that he had not seen this species in Ohio, and Caldwell  (1938) listed only one locality for this state.  Moser  (1958) did not find it in New York and apparently not in Ohio. 

Pachypsylla celtidisgemma

Gall:  Formed in the axillary buds of hackberry, usually polythalmic with one to twelve or more cells; sparsely pubescent in the eastern portion of Texas, covered with a dense matt of long white hair in the western part of the state, intermediate forms occurring where the eastern and western forms come in contact. 

A few problems relative to this species were discovered during the course of this study.  

There are in Texas two forms of bud galls which are distinctly different in appearance  (Plate VIII).  One of these forms is only sparsely pubescent and most of its pubescence is lost in the course of a season.  This form occurs in Central and East Texas, that is, over the part of the state where C. laevigata is the common species of hackberry.  The other form is covered with a dense matt of long white hair which remains on the galls at least during the current season.  This  form occurs In West Texas in areas where C. reticulata is the most common species.  Also it apparently occurs along the entire length of the Rio Grande River at least below Del Rio. At Brownsville this was the only pachypsyllld gall which was found in large numbers.  In addition bud galls of this form were found on the hackberries in northeastern Oklahoma. 

Apparently  the two gall forms are not simply modifications due to development on different host trees.  At Austin and at other localities in Central Texas the sparsely pubescent form was found on trees having the characteristics of C. reticulata as well as on C. laevigata.  Also, near Fredericksburg and in Inks Lake State Park near Bertram a few densely pubescent galls were found on trees with leaves typical of C. laevigata.  On the basis of these observations it was concluded that these two types of galls were due to differences in the gallmakers themselves. 

If the above conclusion is correct it would appear that the gallmakers having a genotype capable of producing densely pubescent galls are adapted to developing on C. reticulata although not limited to trees having the typical features, at least, of this hackberry.  The occurrence of these galls on the population of hackberries along the Rio Grande and on those in northwestern Oklahoma are probably evidence of considerable introgression of C. reticulata characters into the trees of these areas.  This is particularly indicated by the fact that other C. reticulata galls are found on the trees of these regions. 

In Inks Lake State Park and near Laredo some galls were found which appeared  to be clearly intermediate between the two forms, and even at Austin some galls were pubescent enough to approach the western form in appearance.  However, the two forms have not been studied in the field in enough detail to determine with any considerable accuracy either the boundaries of the ranges of the two forms or the width of the zone of intergradation. 

Collection records do indicate that in Central Texas the areas of changeover from the eastern to the western form correspond at least roughly to those areas where C. laevigata is replaced by C. reticulata as the most common hackberry.  Further  they indicate that the zone of intergradation between the two forms is relatively narrow.

The above findings and the fact that no differences were found in the genitalia of specimens from the various collection sites strongly indicates that only a single species of bud pachypsyllld occurs in Texas and, in the opinion of the author, this is probably true for the United States as a whole.  If this can be shown to be true on the basis of later investigations P. pallida and P. dubia, two allied forms described by Patch in 1912 can likely be considered as synonyms of P. celtidisgemma. 

The most plausible Interpretation of the information available in the literature and the observations made in the course of this study would seem to be that there are in the United States two populations of P. celtidisgemma with distinct galls which intergrade in Texas.  There is an eastern "typical" P. celtidisgemma gall and gallmaker which occurs on C. laevigata and the other eastern hackberries, and a western P. pallida gall and gallmaker which occur principally on C. reticulata. Between the two groups of gallmakers there is a very broad zone of intergradation, while between the galls there is a much shorter zone.  This Intergradation is correlated with inter-gradation in Celtis and could presumably be used to some extent as a measure of this intergradation.  Since the form of the gall is a reflection of the physiology of the gallmakers the relatively narrow zone of Intergradation between the gall forms demonstrates that there is a higher degree of host adaptation in the bud gallmakers than would be indicated just on the basis of their coloration.

Possibly P. dubia, on which there is no locality data, represents Intermediates between the P. celtidisgemma and P. pallida forms.

Pachypsylla celtidisinteneris

Gall: Occurring as Inconspicuous blisterlike elevations of the bark on younger stems of hackberry.  They are monothalmic  and  the psyllld cells occur Just beneath the bark.

Range: Texas. P. celtldisinteneris has been previously reported from Iowa, Illinois, Kansas and Ohio.

Pachypsylla celtidismamma  (Riley)  (occidentalis nipple gallmaker)

Gall. This gall is much larger than those of the other nipple galls.  On the upper leaf surface they are seen as cup-shaped depressions 4 to 5 mm in diameter, in the central part of the cup there is either a short projection or a distinct spine. Below the gall projects usually as a vertical cylinder for 5 to 7 mm, the end may be truncated or somewhat irregularly pointed.  Texture rugose reticulate.  Color greenish yellow at maturity, not shining. 

Hosts and distribution:  In view of the numerous forms with which this species has been confused the distribution records for it are somewhat unreliable, but probably it occurs throughout the range of its known host C. occidentalis.  I have seen specimens which could be readily determined as P. celtidismamma from Texas, Oklahoma, Kansas, New York and Delta, Manitoba, and rather definite records are available for it from Ohio and several other midwestern states.  The Texas specimens were collected near the Panhandle towns of Canadian, Miami and Wheeler.

P. celtidispubescens and P. celtldismamma are sympatric  in  northwestern  Oklahoma and adjacent areas of Texas where they often occur on the same trees.  

Pachypsylla celtidisgemma [Riemann considers P pallida a variant of this species]

Gall:  Formed in the axillary buds of hackberry, usually polythalmic with one to twelve or more cells; sparsely pubescent in the eastern portion of Texas, covered with a dense matt of long white hair in the western part of the state, intermediate forms occurring where the eastern and western forms come in contact. 

A few problems relative to this species were discovered during the course of this study.  

There are in Texas two forms of bud galls which are distinctly different in appearance  (Plate VIII).  One of these forms is only sparsely pubescent and most of its pubescence is lost in the course of a season.  This form occurs in Central and East Texas, that is, over the part of the state where C. laevigata is the common species of hackberry.  The other form is covered with a dense matt of long white hair which remains on the galls at least during the current season.  This  form occurs In West Texas in areas where C. reticulata is the most common species.  Also it apparently occurs along the entire length of the Rio Grande River at least below Del Rio. At Brownsville this was the only pachypsyllld gall which was found in large numbers.  In addition bud galls of this form were found on the hackberries in northeastern Oklahoma. 

Apparently  the two gall forms are not simply modifications due to development on different host trees.  At Austin and at other localities in Central Texas the sparsely pubescent form was found on trees having the characteristics of C. reticulata as well as on C. laevigata.  Also, near Fredericksburg and in Inks Lake State Park near Bertram a few densely pubescent galls were found on trees with leaves typical of C. laevigata.  On the basis of these observations it was concluded that these two types of galls were due to differences in the gallmakers themselves. 

If the above conclusion is correct it would appear that the gallmakers having a genotype capable of producing densely pubescent galls are adapted to developing on C. reticulata although not limited to trees having the typical features, at least, of this hackberry.  The occurrence of these galls on the population of hackberries along the Rio Grande and on those in northwestern Oklahoma are probably evidence of considerable introgression of C. reticulata characters into the trees of these areas.  This is particularly indicated by the fact that other C. reticulata galls are found on the trees of these regions. 

In Inks Lake State Park and near Laredo some galls were found which appeared  to be clearly intermediate between the two forms, and even at Austin some galls were pubescent enough to approach the western form in appearance.  However, the two forms have not been studied in the field in enough detail to determine with any considerable accuracy either the boundaries of the ranges of the two forms or the width of the zone of intergradation. 

Collection records do indicate that in Central Texas the areas of changeover from the eastern to the western form correspond at least roughly to those areas where C. laevigata is replaced by C. reticulata as the most common hackberry.  Further  they indicate that the zone of intergradation between the two forms is relatively narrow.

The above findings and the fact that no differences were found in the genitalia of specimens from the various collection sites strongly indicates that only a single species of bud pachypsyllld occurs in Texas and, in the opinion of the author, this is probably true for the United States as a whole.  If this can be shown to be true on the basis of later investigations P. pallida and P. dubia, two allied forms described by Patch in 1912 can likely be considered as synonyms of P. celtidisgemma. 

The most plausible Interpretation of the information available in the literature and the observations made in the course of this study would seem to be that there are in the United States two populations of P. celtidisgemma with distinct galls which intergrade in Texas.  There is an eastern "typical" P. celtidisgemma gall and gallmaker which occurs on C. laevigata and the other eastern hackberries, and a western P. pallida gall and gallmaker which occur principally on C. reticulata. Between the two groups of gallmakers there is a very broad zone of intergradation, while between the galls there is a much shorter zone.  This Intergradation is correlated with inter-gradation in Celtis and could presumably be used to some extent as a measure of this intergradation.  Since the form of the gall is a reflection of the physiology of the gallmakers the relatively narrow zone of Intergradation between the gall forms demonstrates that there is a higher degree of host adaptation in the bud gallmakers than would be indicated just on the basis of their coloration.

Possibly P. dubia, on which there is no locality data, represents Intermediates between the P. celtidisgemma and P. pallida forms.

Pachypsylla sp. (laevigata nipple gallmaker)

Gall: As seen above a circular depression, usually widening internally, bottom of depression flattened with a very short central projection; below the longer galls appear as short cylinders arising from a constricted, shorter ones appear button-like; distal end depressed from an outer rim in center of which there may be a small elevation.  Color tan at maturity, glabrous, shiny.  Size variable, width 3 to 4 mm, length 2 to 4 mm. As previously stated this is thought to be the gall Riley (1890) described as P. celtidiscucurbita variety?

Hosts and distribution:  During this study the galls of this species were found in abundance at only one site, Palmetto State Park, near Luling.  Scattered galls were noted at numerous other sites in Central Texas including around Austin, and a few specimens were found at a site 15 miles west of Oklahoma City. With the exception of some at Palmetto State Park  (Table II) all of these were on trees considered  to be C. laevigata.  In  the case of this exception the morphology of the galls was essentially the same on both hosts.

Some galls rather similar to those occurring on C. laevigata were collected by Dr. John Moser in Maryland from trees thought to be C. tenuifolla.  They differ most markedly (Plate XXX) from the c. laevigata form in being more oval as seen from the side and fit rather well Riley's description of P. celtidiscucurbita.

The C. laevigata and the C. reticulata nipple galls have not yet been found together in a single locality.  Galls of the C. laevigata species were found near Oklahoma City and further collections may demonstrate  that the range of this gallmaker overlaps those of the other nipple galls In this region.

Pachypsylla celtidispubescens

Gall: Above a simple cup-shaped pubescent depression; below spherical, 2 to 3 mm in diameter, covered with white hairs even when the leaf is nonpubescent, green in color until fall then brown.

Hosts and distribution:  This species appears to be essentially restricted  to the range of C. reticulata.  A few galls were found on C. laevigata; these had the same morphology as those found on C. reticulata.  As mentioned  these galls were found to be very numerous on the introgressed hackberries of northwestern Oklahoma, again with typical morphology  in both the galls and the gallmakers.

In Texas galls of P. celtidispubescens were collected at widely separated sites in the western part of the state from Alpine to the Panhandle.  In these collections it was found in large numbers only in the Davis Mountains and In that part of Texas adjoining northwestern Oklahoma as well as at a few other scattered sites.  In many collections it was not found at all or in very low numbers.  For example only a very few specimens were found in the areas around Amarlllo and Lubbock.  It was not found in the area of Austin nor in other areas where C. laevigata is the common  type of hackberry. 

P. celtidispubescens and P. celtldismamma are sympatric  in  northwestern  Oklahoma and adjacent areas of Texas where they often occur on the same trees. 

Pachypsylla celtidisvesicula (occidentalis regular blister gallmaker) 

Gall: Flat, inconspicuous; cell circular, 1 to 2 mm in diameter; slightly elevated above with a slight central protuberance; be-low also slightly projecting with a definite small central nipple. 

Hosts and distribution:  I have seen specimens of this species from Oklahoma, Ohio and Manitoba.  Galls of this type have also been definitely reported from C. occidentalis in Kansas, Ohio, Iowa and New York.  Possibly it occurs to some extent in northern Texas but it has not been there as yet. The adults from all of the three localities mentioned above were found to be very similar In structure.

Pachypsylla laevovesicula n. sp. (laevigata regular blister gallmaker)

Gall:  Like that of P. celtidlsvesicula [Flat, inconspicuous; cell circular, 1 to 2 mm in diameter; slightly elevated above with a slight central protuberance; below also slightly projecting with a definite small central nipple] but larger, cells about 2 mm in diameter at the time of gallmaker emergence.

Hosts and distribution:  This species appears to be essentially restricted to C. laevigata and in Central Texas was found only on trees that could be readily identified as this host.  However, in northwestern Oklahoma it was found on trees having features tending toward C. reticulata and C. occidentalis. 

In Central Texas P. laevovesicula was found  to be second in abundance only to P. celtidisasterisca among the blade pachypsyllids of C. laevigata and in some environments it was found to be the most numerous one.

Pachypsylla reticulovesicula n. sp. (reticulata regular blister gallmaker)

Gall: Like that of P. celtidisvesicula [Flat, inconspicuous; cell circular, 1 to 2 mm in diameter; slightly elevated above with a slight central protuberance; below also slightly projecting with a definite small central nipple] but larger, diameter of cells 2.5  to 3.1 mm at time of gallmaker emergence.  Toward  the end of the season galls of this species typically turn brown on the upper surface over the cells. 

Hosts and distribution:  This species appears to be essentially host specific for C. reticulata and was found in almost all areas where its host was found.  In the area of Austin it is the only blade pachypsyllld which occurs on C. reticulata in sizable numbers.

Pachypsylla celtidisasterisca Riley (star gallmaker)

This gall is quite characteristic and readily recognized from Riley's  (1890) description.  Wells  (1920) described in detail the morphology of galls collected near Denton, Texas and included in his paper an excellent drawing of one, apparently the only such illustration which has been published.  

Gall: Blister-like, somewhat elevated above and below; above with a short central spine 1 to 2 mm in length which is frequently broken off, below with a central projection which, arising from a narrow base spreads out and divides to assume the form of a small flower or star, sometimes the projection does not spread out in the galls found on C. reticulata but instead forms a hollow tube 2 to 3 mm in length.  Cells circular, about 4 mm in diameter at the time of gallmaker emergence. 

Hosts and Distribution:  In Central Texas P. celtidlsasterisca is the most abundant leaf pachypsyllld  and this is perhaps true for the state as a whole in which it was found in nearly all areas of collection.  This is the only free living species of the Texas blade pachypsyllids which is apparently not host specific for either C. reticulata or C. laevigata. However, in the overlap zone between the two hosts in Central Texas there is a very pronounced host preference for C. laevigata indicating that there are possibly two races of P. celtidisasterisca in Texas.  This will be discussed  in greater detail in a later section.  It was found on trees having major features of C. occidentalis in Oklahoma but as it apparently hasn't been reported from the midwestern and northeastern states it may not extend Into the main part of the range of this hackberry.

Pachypsylla rugosa n. sp. (rough blister gallmaker) 

Hosts: Celtis reticulata, laevigata

Gall: One to several cells occurring together; distinctly elevated above and below; veins over gall enlarged and prominent particularly above over the central part of the cell, below a small central nipple which is often obscured by the enlarged veins. 

The galls of this species is easily distinguished from those of the other blister gallmakers by their greater elevation and very prominent venation.  Sometimes, however, these galls are closely associated with the galls of another species, such as P. celtidisasterisca, so that they may not be readily apparent.  Unless caution is used in rearing adults from such galls the species may become mixed. 

Hosts and distribution:  This species appears to be mostly restricted  to C. reticulata although large numbers were found on what appeared  to be C. laevigata near Seymour, Texas.  It was found in many areas of western Texas in the range of its host but it has not yet been found in the Austin area.

A study of the hackberry gallmaker genus Pachypsylla (Homoptera: Psyllidae)