Influence of developmental conditions on cold-hardiness of adult Dalbulus leafhoppers: implications for overwintering
1993
Larsen, K.J. | Lee, R.E. Jr | Nault, L.R.
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.
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