EUROPEAN JOURNAL OF ENTOMOLOGY

Eur. J. Entomol. 101 (2): 231-236, 2004

Supercooling capacity and cold hardiness of the eggs of the grasshopper Chorthippus fallax (Orthoptera: Acrididae)

Shu-Guang HAO, Le KANG^*

State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, The Chinese Academy of Sciences, 25 Beisihuanxi Road, Haidian District, Beijing 100080, China

Cold tolerance of the eggs of the grasshopper, Chorthippus fallax (Zubovsky), was examined in the laboratory. Egg supercooling points varied from -6°C to -32.4°C and could be divided into two groups. The supercooling points of the higher SCP group ranged from -6°C to -14°C and those of lower SCP group from -21.8°C to -32.4°C. Although low temperature acclimation could slightly decrease the supercooling points of eggs, the effect was not significant for all embryonic developmental stages or acclimation periods. The supercooling capacity was obviously different between pre-diapause, diapause and post-diapause embryonic stages. The mean supercooling points of pre-diapause and diapause eggs were similar; -28.8 ± 1.6°C and -30.7 ± 1.0°C for non-acclimated eggs and -29.5 ± 1.3°C and -31.18 ± 0.8°C for acclimated eggs respectively. However, the mean supercooling points of post-diapause eggs were significantly higher; -12.9 ± 5.6°C for non-acclimated and -13.5 ± 4.5°C for acclimated eggs respectively. The survival rates of diapause eggs at > -25°C were not significantly different from that at 25°C, but survival rates at < -30°C decreased significantly. The lethal temperature (Ltemp₅₀) for a 12 hrs exposure was -30.1°C, and the lethal time (Ltime₅₀) at -25°C was 44 days. Since the SCPs of diapause eggs was similar to their Ltemp₅₀, we may consider the supercooling capacity of such eggs is a good indicator of their cold hardiness and the species is a true freeze avoiding insect. Based on the analysis of local winter temperature data, pre-diapause and diapause, low SCP eggs can safely survive severe winters, but not the post-diapause, high SCP eggs. The importance of the overwintering strategy and the relationship between diapause and cold hardiness of this species is discussed.

Keywords: Cold hardiness, supercooling point, acclimation, overwintering ability, Chorthippus fallax

Received: April 2, 2003; Revised: July 16, 2003; Accepted: September 12, 2003; Published: June 25, 2004  Show citation