Archivos de diario de octubre 2022

14 de octubre de 2022

Notes and identity of the Burrobrush Gall Psyllid

I. Background. When I first moved to Tucson five years ago in the winter of 2018, one of the first plants I recorded was a ragweed-like bush with long thin leaves covered with numerous dried flowers. Upon posting to inat, local plant expert Steve Jones identified this plant to be Ambrosia monogyra (Singlewhorl Burrobrush) and informed me that those "flowers" were in actuality galls, but he didn't know what insect was responsible for them.

Later that year, Steve would go on to investigate the galls more closely and photograph the insect inside, but it would take me another 3 years to notice this observation and realize the insect he had photographed was not a gall midge like I would have expected but a psyllid.

Steve's psyllid was a nymph, and while nymphs are difficult to identify I determined that it belonged to the genus Craspedolepta, a holarctic genus typically associated with plants in the family Asteraceae. With over 40 species, Craspedolepta is the second most diverse genus of psyllids in North America, although none are known from Ambrosia, raising questions on whether this psyllid was in fact the gall inducer or just an incidental/inquiline. Later that year, James Bailey would go on to photograph more Craspedolepta nymphs inside Ambrosia monogyra galls which seemed to answer that question, but raise another: what species of Craspedolepta induces galls on Ambrosia monogyra? Is it an undescribed species?

Nymphs from burrobrush galls. (image credits: left: Steve Jones. Right: James Bailey)

In October, 2022, I investigated gall-covered Ambrosia monogyra and was able to find three adult female psyllids, which I have identified to be Craspedolepta lapsus.

II. Identification. Adult Craspedolepta can be recognized among the North American psyllid fauna by the following combination of characters: genal cones absent, pterostigma absent, vein R+M+Cu bifurcating into veins R & M+Cu, vertex wider than long, antennae shorter than 2x head width, and the clypeus not long and tubular. Craspedolepta in North America can be subdivided into approximately 4 groups which may or may not be strictly monophyletic but are useful in species recognition. These groups can be summarized as follows:

  1. C. angustipennis group: Species with white-ish wings covered in dark spots, usually on Artemesia
  2. C. veaziei group: Species with yellowish to clear wings, usually covered in dark spots, usually on Solidago
  3. C. vulgaris group: Species with yellowish to clear wings, without spots, usually on Solidago
  4. C. nebulosa group: Species associated with fireweed

Several exceptions, such as Craspedolepta sonchi or C. eas, don't fall into any of these groups but are easily identifiable and do not need to be considered for the purpose of this study.

The psyllids collected were determined to belong to the Craspedolepta vulgaris group by reference to the spotless yellow wings and a total length over 3.5mm. However, certain species of the C. veaziei group may rarely fit these characteristics as well, so both of these groups were considered for the purposes of this study.

In addition to the presence or absence of wing maculation, characters useful for species-level diagnosis in the genus Craspedolepta include the arrangement of the surface spinelets on the wings, the shape of the head in dorsal view, the length of the antennae and number of antennae segments, the shape of the clypeus in lateral view, the total length, and the male and female genitalia. These characters are discussed in the following sections.

Surface spinelets. Surface spinelets are minute setae on the wings which are generally only visible at high magnification but may sometimes be visible in very high definition photos. The relative density of these spinelets may be useful in diagnosing species, and in some species they are arranged to form a hexagonal pattern. A summary of the surface spinelets for veaziei and vulgaris group species is given as follows:

Veaziei group
C. veaziei, C. caudata, C. numerica, C. nota, C. macula, C. fumida: spinelets arranged in a roughly hexagonal pattern
C. maculimagna, C. oregonensis: spinelets sparse, no pattern

Vulgaris group
C. vulgaris, C. parvula, C. constricta, C. furcata, C. minuta, C. flavida, C. ochracea: spinelets arranged in a roughly hexagonal pattern
C. magna, C. lapsus, C. scurra: spinelets sparse, no pattern

Head characters. Characters relating to the head and antennae may occasionally be useful in Craspedolepta species determination but were not necessary for this study.

Total length. Length is measured from the head to the wingtips. Craspedolepta generally measure between 1.5 to 4mm with females typically larger than males, but the size is relatively constant for each species.

A summary of the average lengths of veaziei and vulgaris group females is given as follows:

Veaziei group females in mm
2.8 ± 0.13 C. veaziei
2.6 ± 0.06 C. caudata
2.3 ± 0.03 C. numerica
2.7 ± 0.20 C. nota
2.8 ± 0.09 C. macula
3.1 ± 0.13 C. maculimagna
2.5 ± 0.06 C. oregonensis
3.6 ± 0.17 C. fumida

Vulgaris group females in mm
3.5 ± 0.13 C. magna
3.1 ± 0.17 C. vulgaris
2.5 ± 0.10 C. parvula
3.0 ± 0.12 C. constricta
3.3 ± 0.17 C. furcata
2.5 ± ?.?? C. minuta (missing pages 68-69 from Journet & Vickery, unable to assess)
3.9 ± ?.?? C. lapsus (only 1 female analyzed by Journet & Vickery, so average measurements are unknown)
3.2 ± 0.09 C. flavida
3.6 ± 0.10 C. scurra
3.6 ± 0.14 C. ochracea

In general, species of the veaziei group (spotted wings) are smaller than species of the vulgaris group (spotless wings), with a few exceptions. Only C. fumida and C. maculimagna exceed 3.0mm, and of these only C. fumida is described as being occasionally spotless. The typical spotted form of C. fumida may be distinguished by all other members of the veaziei group easily by its size, but the potential of spotless forms means that it must be considered when trying to diagnose spotless specimens (>3.0mm). The opposite is true of the relatively small spotless members of the C. vulgaris group, C. parvula and C. minuta. Females of the C. angustipennis group need not be considered for this study, but all species measure less than 3.0mm except the densely-spotted C. maculidracunculi (3.1mm).

Genitalia. Male genitalia is often more useful than female genitalia in species determination, but there are several exceptions. In particular, C. caudata and C. numerica have a distinctly downcurved dorsal valve, C. constricta and C. lapsus have an abruptly narrowed dorsal valve, and C. furcata has a distinctly abbreviated ventral valve. Differences between other species are much more slight. The genitalia for all members of the veaziei and vulgaris groups are illustrated here (source: modified from Journet & Vickery 1979):

Figures. 1. C. veaziei, 2. C. caudata, 3. C. numerica, 4. C. nota, 5. C. macula, 6. C. maculimagna, 7. C. oregonensis, 8. C. fumida, 9. C. magna, 10. C. vulgaris, 11. C. parvula, 12. C. constricta, 13. C. furcata, 14. C. minuta, 15. C. lapsus, 16. C. flavida, 17. C. scurra, 18. C. ochracea

III. Methods. Two adult female Craspedolepta were collected from Ambrosia monogyra and were analyzed in regard to the above outlined characters. Surface spinelets were assessed microscopically using 100x magnification.

IV. Results. Collected females were measured to be 3.6 and 3.7mm. A microscopic analysis of the surface spinelets revealed that the spinelets were sparse, not arranged in a distinctly hexagonal pattern. The female genitalia of both specimens were compared to Journet & Vickery's illustrations.

The large size coupled with the sparse spinelet distribution instantly excludes the entire veaziei group and most members of the vulgaris group except C. magna, C. lapsus, and C. scurra. The genitalia proved to be distinctive however, with the dorsal plate abruptly narrowed before the apex, a character only seen in C. lapsus (compare fig 15 above, and please ignore the bad lighting - still working on a way to take better illuminated microscope pics)

V. Conclusions. Craspedolepta lapsus was described from a small series of adults from Davis, Texas, and the host plant and life history of the species were until now unknown. Two assumptions are made here: the identification of the psyllids examined here as Craspedolepta lapsus assumes that there is not an undescribed species which has a female with identical characteristics as C. lapsus, and the association of this species with burrobrush galls assumes that there are not more than one Craspedolepta species associated with Ambrosia monogyra. Further study and collection may shed light on whether these hypotheses could be true. No male psyllids could be found for examination in the current study.

Burrobrush galls can be fairly common locally in Arizona, but it is likely that this psyllid occurs throughout the range of the hostplant, at least to western Texas. An examination of Ambrosia monogyra observations on iNaturalist may yield further information about this insect's range. Nymphs have been found in July and August (iNat observations), and adults have been recorded from September and October. While many plants were heavily galled in October, I was not able to find any nymphs inside galls at this time, though I did find several nymph exuviae. The complete life history and development period of this psyllid remains unknown at this time.

Publicado el octubre 14, 2022 12:51 TARDE por psyllidhipster psyllidhipster | 6 comentarios | Deja un comentario