Biological Evidences For The Primary Role Of Aphid Flight Dispersal In The Dissemination Of Obligate Aphid Pathogens (Entomophthorales)

The fungal order Entomophthorales includes numerous species of obligate aphid pathogens that frequently cause epizootics in aphid populations worldwide. The source of primary infection is of general significance for understanding the epizootiological process of aphid mycoses but is poorly understood. Although several possible means have been explored in relation to dissemination of the obligate aphid pathogens, it is hypothesized that their dispersal is more likely to be associated with host flight behavior. This study sought to test this hypothesis by examining species and frequencies of fungal pathogens borne by migratory alates trapped from air in nature and demonstrating the capabilities of host alates in postinfection flight, postflight colonization, premycosis fecundity and fungal transmission to their progeny via simulation flight experiments in laboratory. Pandora neoaphidis, a common obligate aphid pathogen without resting spores, was emphasized in association with English grain aphid Sitiobion avenae and green peach aphid Myzus persicae as hosts. Species and frequencies of fungal pathogens borne by migratory alates from airMyzus persicae. From late October 2001 through early January 2002, migratory alates of M. persicae from air were daily trapped to potted cabbage plants on a large piece of yellow waterproof cloth, which was flattened on the roof of a 6-floor huge building at the Huajiachi campus of Zheiang University (N30°14\ E120°09') in Hangzhou, Zhejiang. The daily trapped alates were carried to laboratory for determining fungal infection by individually rearing them for 7 days on detached cabbage leaves in Petri dishes. During the 80-day period, a total of 760 alates were trapped from air and 266 (35%) were found bearing fungal infection in subsequent rearing and examination. Of the infected alates, 87.3% died from mycosis within three days and the rest died in the following two days. Entomophthoralean infection was observed in 94.4% of the mycosed alates whereas the rest suffered from infection by Beauveria bassiana. Among the alates killed by the Entomophthorales, P. neoaphidis took a proportion of 66.1%, Zoopthora anhuiensis 22.6%, Entomophthora planchoniana 9.7% and Neozygities fresenii 1.6%, respectively. Two alates were found suffering from cross infection of P. neoaphidis with Z. anhuiensis or N. fresenii. All entomophthoralean species found in the migratory alates were obligate aphid pathogens.From 19 October through 17 December 2002, 310 M. perciae alates were trapped at the same location and individually reared for daily observation for 12 days. Of those, 130 werefound being infected with fungal pathogens, taking 41.9% in total. P. neoaphidis occurred at a frequency of 84.4% among the infected alates, Z. anhuiensis at 3.1%, Conidiobolu obscurus at 10.9%, N. fresenii at 1.6% and E. planchoniana at 0.8%. All the alates infected with the obligate aphid pathogens died from mycosis within the first five days after collection. Two other alates were infected with hyphomycetous fungi B. bassiana and Verticillium lecanii, respectively. Subsequently, contagious infection was observed in the progeny colonies initiated by the infected alates, implying successful transmission of the fungal infection from the alates to their progeny. Secondary infection occurred in 37 (28.5%) of the colonies and resulted in tertiary infection in 12 colonies (9.2%) during the 12-day period.Cereal aphids. Another trap was set to collect migratory alates of cereal aphids from air on the roof of a building at the town of Yuanyang County (N 35°03', E 113°57'), Henan Province from 1 April to late May 2002. A total of 1092 alates from air were trapped to potted wheat plants on the building, including 415 S. avenae, 642 Rhopalosiphum padi, 22 Metopolophium dirhodum, and 13 Schizaphis graminum. Reared individually on seedlings in glass tubes for 7 days, 341 of the trapped alates were found bearing three species of obligate aphid pathogens in the Entomophthorales and died from mycosis within the first five days after rearing, tak...