Variation in cold hardiness of Liriomyza huidobrensis (Diptera: Agromyzidae) along latitudinal gradients

Liriomyza huidobrensis Blanchard (Diptera: Agromyzidae) is an economically important pest around the world. The insect was first reported in China in 1993, and now has spread to >10 provinces, ranging from subtropical to temperate regions. Supercooling capacity and cold survival ability of pupal L. huidobrensis were investigated in eight populations along a latitudinal gradient: latitude 25degrees01' N to latitude 42degrees16' N. A northern distribution limit was proposed based on cold tolerance and the lowest monthly mean temperature of the year. The pattern of variation in cold tolerance with latitude differed for populations on different sides of the border. From the southern-most population in Kunming to the northern marginal population in Xi'an, cold tolerance of L. huidobrensis increased with latitude as measured by low lethal time (Ltime(50)) at -5degreesC. Field populations can depress their supercooling point 3.6degreesC between the spring geographic populations at the two extremes. Cold tolerance also was enhanced significantly by prechilling of pupal L. huidobrensis at 0, 5, and 10degreesC. Both acclimation at 5 and 10degreesC for 8 d resulted in the maximum observed survival rate. Therefore, south of the distribution limit, L. huidobrensis can successfully overwinter and persist as a source population, continually supplying insects for further reinfestation or dispersal. However, populations beyond the-northern border did not show the enhanced cold tolerance with increasing latitude. Most of the leafminers there survived severe winter condition by opportunistic exploitation of protected microhabitats. Our results may facilitate future predictions of range expansion and integrated management of this pest.