Table 2 Bioclimatic variables chosen for modeling and their association with the habitat preferences of Ch. stipae stipae and Stipa species.

Bio01

Annual Mean Temperature [°C]

This variable approximates the total energy inputs for an ecosystem⁸⁹. As individuals of the Ch. stipae stipae inhabit various steppe ecosystems (typical temperate steppe and Alpine-steppe), we want to know what temperature ranges are optimal.

Bio10

Mean Temperature of Warmest Quarter [°C] – mean temperatures during the warmest three months of the year (in this case – June, July, and August)

As Ch. stipae stipae is considered a strictly xerothermophilous subspecies⁹⁰, temperature and precipitation during the warmest period of the year are important for its habitat. This period is also critical for aphids because day length, temperature, and nutrition are recognized as the most important factors which influence the production of sexuales (oviparous females and males) in autumn⁹¹.

Bio15

Precipitation Seasonality [mm] – a measure of the variation in monthly precipitation totals during the year or averaged years

As with variable Bio01, we wanted to know what range of precipitation is optimal for the occurrence of this aphid.

Bio18

Precipitation of Warmest Quarter [mm]

See the description of the variable Bio10.

Bio04

Temperature seasonality [°C] – a measure of temperature change during the year or averaged years

This variable was included in the analyses because steppes exhibit a wide variation of temperature, both during the year and the day

Bio10

Mean Temperature of Warmest Quarter [°C] – mean temperatures during the warmest three months of the year (in this case – June, July, and August)

Since the Miocene, dry grasslands are linked to the warm and dry climate⁹², temperature and precipitation during the warmest period of the year seems very important for this type of vegetation. Warm summers combined with low precipitation generally reduce the presence of trees thus allowing the development of grass vegetation.

Bio14

Precipitation of Driest Month [mm]

For the Great Steppe, driest months occur in the winter (mostly February). Winter precipitation penetrates deeper into the soil. Conversely, summer precipitation evaporates before infiltration⁹³.

Bio15

Precipitation Seasonality [mm] – a measure of the variation in monthly precipitation totals during the year or averaged years

Steppes are characterized by low precipitation – we want to see of precipitation variability during the year.

Bio18

Precipitation of Warmest Quarter [mm]

See the description of variable Bio10.