Background
The authors write that the majority of central European orthopterans (an order of insects that includes grasshoppers, crickets and locusts) "are flightless and have low dispersal ability," citing Reinhardt et al. (2005). However, they note that "since the 1980s - the beginning of the strong global temperature increase - some short-winged (brachypterous) species have been able to expand their ranges rapidly," as reported by Thomas et al. (2001), Simmons and Thomas (2004), Gardiner (2009), and Wissmann et al. (2009); and they say that in those cases, "long-winged (macropterous) individuals of the predominantly short-winged (flightless) species are assumed to have been responsible for the range shifts," citing the findings and conclusions of Simmons and Thomas (2004), Gardiner (2009), and Hochkirch and Damerau (2009).

What was done
Poniatowski and Fartmann studied the migration behavior of Metrioptera roeselii, a medium-sized bush-cricket, 13-26 mm in total length, which is currently expanding its range northwards in large parts of Europe (Kleukers et al., 2004; Gardiner, 2009; Wissmann et al., 2009)." This species is actually wing-dimorphic, but they indicate that "the short-winged (brachypterous) morph dominates."

What was learned
Based on their analyses of the relationships between bush-cricket densities and several meso-climate/weather parameters, the two German researchers found that cricket abundances were positively correlated with warm and dry weather conditions during the hatching times of the nymphs, which led them to conclude that "the development of long-winged individuals is determined by density stress (crowding), as has been shown for locusts (Uvarov, 1966)," while further noting that "similar results have also been reported for other bush-crickets," citing Ando and Hartley (1982), Sanger (1984) and Higaki and Ando (2003).

What it means
In light of these several discoveries, Poniatowski and Fartmann conclude that "the rapid northward range expansion of M. roeselii is indirectly driven by climate change," explaining that "favorable (warm/dry) weather conditions lead to high densities at high latitudes (cf. Bale et al., 2002) and in turn result in many macropters," which are the "potential dispersers" that get the species where it needs to go in order to survive in a world of evolving warmth.

References
Ando, Y. and Hartley, J.C. 1982. Occurrence and biology of a long-winged form of conocephalus discolor. Entomologia Experimentalis Applicata 32: 238-241.

Bale, J.S., Masters, G.J., Hodkinson, I.D., Awmack, C., Bezemer, T.M., Brown, V.K., Butterfield, J., Buse, A., Coulson, J.C., Farrar, J., Good, J.E.G., Harrington, R., Hartleuy, S., Jones, T.H., Lindroth, R.L., Press, M.C., Symrnioudis, I., Watt, A.D. and Whittaker, J.B. 2002. Herbivory in global climate change research: direct effects of rising temperature on insect herbivores. Global Change Biology 8: 1-16.

Gardiner, T. 2009. Macropterism of Roesel's bushcricket Metrioptera roeselii in relation to climate change and landscape structure in Eastern England. Journal of Orthoptera Research 12: 95-102.

Higaki, M. and Ando, Y. 2003. Effects of crowding and photoperiod on wing morph and egg production in Eobiana engelhardti subtropica (Orthoptera: Tettigoniiade). Applied Entomology and Zoology 38: 321-325.

Hochkirch, A. and Damerau, M. 2009. Rapid range expansion of a wing-dimorphic bush-cricket after the 2003 climatic anomaly. Biological Journal of the Linnean Society 97: 118-127.

Kleukers, R.M.J.C., van Nieukerken, E.J., Ode, B., Willemse, L.P.M. and van Wingerden, W.K.R.E. 2004. De sprinkhanen en krekels van Nederland (Orthoptera). In: Nederlandse Fauna 1, 2nd Edition, National Natuurhistorisch Museum, KNNV Uitgeverij & EIS-Nederland, Leiden, The Netherlands.

Reinhardt, K., Kohler, G., Maas, S. and Detzel, P. 2005. Low dispersal ability and habitat specificity promote extinctions in rare but not in widespread species: the Orthoptera of Germany. Ecography 28: 593-602.

Sanger, K. 1984. Die Populationsdichte als Ursache makropterer Okomorphosen von Tessellana vittata (Charp.) (Orthoptera, Tettigoniidae). Zoologischer Anzeiger 213: 68-76.

Simmons, A.D. and Thomas, C.D. 2004. Changes in dispersal during species' range expansions. American Naturalist 164: 378-395.

Thomas, C.D., Bodsworth, E.J., Wilson, R.J., Simmons, A.D., Davies, Z.G. Musche, M. and Conradt, L. 2001. Ecological and evolutionary processes at expanding range margins. Nature 411: 577-581.

Uvarov, B.P. 1966. Grasshoppers and Locusts: A Handbook of General Acridology, Volume 1. Cambridge University Press, Cambridge, United Kingdom.

Wissmann, J., Schielzeth, H. and Fartmann, T. 2009. Landscape-scale expansion of Roesel's bush-cricket Metrioptera roeselii (Orthoptera: Tettigoniidae) at the north-western range limit in Central Europe. Entomologia Generalis. 31: 317-326.