Opportunism of Conidiobolus obscurus stems from depression of infection in situ to progeny colonies of host alatae as disseminators of the aphid‐pathogenic fungus

Abstract

Conidiobolus (Entomophthorales: Ancylistaceae) includes common aphid pathogens but causes sporadic mycosis worldwide. This epizootiological opportunism was explored herein by examining the potential of mycosis transmission in the progeny colonies of 513 Myzus persicae alates as disseminators of C. obscurus often infecting aphids. The alates exposed to spore showers were flown for 2.05 (0.01-8.95) km on flight mills and then reared individually on cabbage at 20-23 degrees C for 14 day colonization. All truly infected alates were mycosed within 6 days and averagely left 3.9 (0-15) nymphs while those uninfected produced 11.6 (0-35) nymphs during the same period. Secondary and tertiary infections occurred only in 16.2% and 4.8% of the progeny colonies of the mycosed alates respectively, due to c. 60% of the cadavers forming resting spores. Most of the contagious infections appeared on days 4-8 after colonization and no more occurred from day 11 onwards. Trends of colony sizes (last-day averaging 51.5 aphids) and mycosis transmission (sixth-day maximum 6.3%) fit well to logistic (r2 = 0.99) and Gompertz growth models (r2 = 0.91) respectively. The results confirm that the opportunism of C. obscurus stems from depression of contagious infection after dissemination by host alates and suggest that it be overwhelmed by the prevalence of other non-resting fungal species.

Biotic and abiotic regulation of resting spore formation in vivo of obligate aphid pathogen Pandora nouryi: Modeling analysis and biological implication

“…As a life strategy, fungal pathogens form resting spores to survive in situ for the forthcoming host absence, as shown in this study, or spread to where host is available. The alatae infected by Entomophthorales, irrespective of obligate or non-obligate and of forming or not forming RS, have proven to spread with aphid dispersal flight and to establish infection sites in colonized cohorts Chen and Feng, 2006;Zhang et al, 2007;. The lower temperatures of 15-20°C and the longer day lengths of 12-16 h found to enhance the proportions of aphid cadavers forming RS at lower spore concentrations in this study fall in optimal ranges for most of fungus-aphid interactions and are well in accordance with the features of growing seasons which are synchronized with aphid epizootics in the field (Wilding and Perry, 1980;Feng et al, 1991;McLeod et al, 1998;Hatting et al, 2000;Nielsen et al, 2001;Nielsen and Hajek, 2005).…”

“…Most aphid-pathogenic Entomophthorales, irrespective of obligate or non-obligate species, may form resting spores (zygospores or azygospores; RS) to survive adversity (e.g., host absence) in their life cycles (Barta and Cagáň , 2006). RS formation in vivo reduces drastically the production of primary conidia, which are discharged from cadavers and infect aphid cohorts where the cadavers are located, and causes interruption of fungal infection cycle (Zhang et al, 2007). Thus, exploring mechanisms involved in the RS formation of the aphid pathogens would help understand the seasonal prevalence of aphid mycoses.…”

Entomopathogenic fungi and insect behaviour: from unsuspecting hosts to targeted vectors

“…Various species of entomopathogenic fungi have been identified in migratory alate aphids trapped from the air (Chen and Feng 2004a;Feng et al 2007;Huang, et al 2008). Zhang et al (2007) found that the dispersal ability of alate M. persicae that were inoculated with Conidiobolus obscurus (Hall & Dunn) (Zygomycota: Entomophthorales) was not different to uninfected aphids and, following dispersal, infected aphids were able to reproduce and transmit the pathogen to their progeny. Several other species of aphid have been recorded as transmitting entomopathogenic fungi when migrating as alates, including S. avenae, Rhopalosiphum padi (L.) and Schizaphis graminum (Rondani) (Feng et al 2004).…”

Resting spore formation of aphid‐pathogenic fungus Pandora nouryi depends on the concentration of infective inoculum

“…This finding is of general importance for deep insights into seasonal prevalence and survival strategy of P. nouryi and possibly related fungal pathogens. Resting spore formation of an insect pathogen implies interruption of infection in situ until new infection cycle begins in the following seasons (Eilenberg and Pell, 2007; Zhang et al ., 2007). In nature, high concentrations of conidia discharged onto host aphid colonies or plants they inhabit are likely to achieve at the time of an epizootic that often produces high‐density mycosed cadavers.…”