Influence of developmental conditions on cold‐hardiness of adult Dalbulus leafhoppers: implications for overwintering

Little is known about how adults of the corn leafhopper, Dalbulus maidis (DeLong & Wolcott), and its congeners survive subfreezing temperatures at high elevations during the dry winter in Mexico. In the laboratory, duration of survival at −5 °C was measured for four Mexican Dalbulus species: D. maidis, D. elimatus (Ball), D. gelbus DeLong and D. quinquenotatus DeLong & Nault; and a closely related North American species, Baldulus tripsaci Kramer & Whitcomb. Adult leafhoppers reared under environmental conditions that simulated the beginning of the dry winter season during October in Mexico (‘October‐reared’) were at least twice as tolerant of −5 °C than adults reared under environmental conditions that simulated the beginning of the wet summer season during June (‘June‐reared’). Dalbulus species found primarily at high elevations, such as D. elimatus, were seven times more tolerant of −5 °C than D. quinquenotatus, a species which overwinters at low to mid elevations on its Tripsacum hosts. October‐reared D. maidis adults survived relatively short periods at −5 °C (LT50 = 8.9 h) compared to October‐reared D. elimatus adults (LT50 = 42.3 h). This suggests that in Mexico, D. maidis either overwinters in protected habitats at higher elevations or it migrates to lower, frost‐free regions. October‐reared B. tripsaci adults, which overwinter in the egg stage, were intolerant of −5 °C (LT50 = 2.6 h). A conditioning period for 1 h at +5 °C before and after exposure to −5 °C significantly improved survival for D. maidis. Supercooling points (SCPs) were between −23 and −20 °C, indicating that mortality of these leafhoppers at −5 °C was due to cold shock injury rather than internal ice formation.