Box 63 Climatic modeling for fruit flies

km

The Queensland fruit fly, Bactrocera tryoni, is a pest of most commercial fruits. The females oviposit into the fruit and larval feeding followed by rotting quickly destroys it. Even if damage in an orchard is insignificant, any infestation is serious because of restrictions on interstate and overseas marketing of fruit-fly-infested fruit.

CLIMEX has been used by R.W. Sutherst and G.F. Maywald to describe the response of B. tryoni to Australia's climate. The growth and stress indices of CLIMEX were estimated by inference from maps of the geographical distribution and from estimates of the relative abundance of this fly in different parts of its range in Australia. The map of Australia depicts the ecoclim-atic indices (EI) describing the favorableness of each site for permanent colonization by B. tryoni. The area of each circle is proportional to its EI. Crosses indicate that the fly could not permanently colonize the site.

The potential survival of B. tryoni as an immigrant pest in North America can be predicted using CLIMEX by climate-matching with the fly's native range. Accidental transport of this fly could lead to its establishment at the point of entry or it might be taken to other areas with climates more favorable to its persistence. Should B. tryoni become established in North America, the eastern seaboard from New York to Florida and west to Kansas, Oklahoma, and Texas in the USA, and much of Mexico are most at risk. Canada and most of the central and western USA are unlikely to support permanent colonization. Thus, only certain regions of the continent are at high risk of infestation by B. tryoni and quarantine authorities in those places should maintain appropriate vigilance. (After Sutherst & Maywald 1991.)

history such as a medieval 12 th century warm event and the 17th century Little Ice Age when "Ice Fairs" were held on the frozen River Thames. Inferred changes in temperatures range from 1 to 6°C, sometimes over just a few decades.

Confirmation of past temperature-associated biotic changes leads to the advocacy of such models to predict future range changes. For example, estimates for disease-transmitting mosquitoes and biting midges under different climate-change scenarios have ranged

Fig. 6.15 Modeled distribution for Austrochlus species (Diptera: Chironomidae) based on presence data. Black, predicted presence within 98% confidence limits; pale grey, within 95% confidence. (After Cranston et al. 2002.)

Fig. 6.15 Modeled distribution for Austrochlus species (Diptera: Chironomidae) based on presence data. Black, predicted presence within 98% confidence limits; pale grey, within 95% confidence. (After Cranston et al. 2002.)

from naive estimates of increased range of disease vectors into populated areas currently disease-free (where vectors actually already exist in the absence of the virus) to sophisticated models accounting for altered development rates for vector and arbovirus, and altered environments for larval development. Future levels of predicted climate change remain unclear, allowing certain policy makers to deny its existence or its biotic significance. However, by the turn of the millennium Europe had warmed 0.8°C in the 20th century and realistic expectations are for a further increase of between 2.1 and 4.6°C mean global change in this century, along with commensurate variation in other climatic factors such as seasonality and rainfall. That predicted changes in distributions of insects are occurring is evident from studies of individual species, but the generality of these examples has been unclear. However, a study of species of western European butterflies (limited to non-migrants and excluding monophagous and/or geographically restricted taxa) is quite conclusive. Significant northward extension of ranges is demonstrated for many taxa (65% of 52 species), with some stasis (34%), and retraction south from an earlier northern limit for only one species. Data for the southern boundary, limited to 40 species, revealed retraction northward for 22%, stasis for 72%, and southward extension for only one species. The sub set of the data for which sufficient historical detail was known for both northern and southern boundaries comprised 35 species: of these 63% shifted northward, 29% were stable at both boundaries, 6% shifted southwards, and one species extended both boundaries. For the many species whose boundaries moved, an observed range shift of from 35 to 240 km in the past 30-100 years coincides quite closely with the (north) polewards movement of the isotherms over the period. That such range changes have been induced by a modest temperature increase of <1°C surely is a warning of the dramatic effects of the ongoing "global warming" over the next century.

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