spores produced Entomophaga maimaiga infecting the gypsy moth Lymantria dispar Ann E. Hajek and Mitsuaki Shimazu Abstract: We investigated the association of environmental factors (temperature, photoperiod, host molting status) and fungal factors (isolate, dose, strain attenuation) with the production of conidia versus resting spores by the entomopathogenic fungus Entomophaga maimaiga infecting the lamae of the gypsy moth Lymantria dispar. Fungal spores produced from individual cadavers of lamae killed by E. maimaiga can include conidia discharged from the cadaver surface, resting spores (azygospores) within the cadaver, or both spore types. The single factor having the greatest impact on the type of spore produced was host age; second instars virtually never contained resting spores, independent of temperature, while fifth instar cadavers contained resting spores more frequently at higher temperatures. However, there was increased conidiation at lower temperatures. Photoperiod was the only factor studied that did not significantly influence the type of spore produced. Resting spore production was negatively associated with the molting cycle; cadavers of those lamae that molted or exhibited premolt characteristics during the period between infection and death contained fewer resting spores. Increased fungal dose yielded more resting spores, as did extensive serial passage, which simultaneously caused a decrease in conidiation. Fungal isolates varied in the types of spores produced, with fewer cadavers of lamae killed by the least virulent isolate discharging conidia. Results from this study support the hypothesis that both the condition of the fungal pathogen as well as the environment surrounding it contribute to the types of spores produced. Key words: fungal sporulation, resting spores, azygospores, Entomophthorales, Entomophaga maimaiga, biological control. RCsumC : Les auteurs ont examink l'association des facteurs environnementaux (tempkrature, photopCriode, Ctat de mue de l'hbte) et fongiques (isolat, dose, attCnuation des souches) avec la production de conidies, versus des spores de repos, par le champignon entomopathogkne Entomophaga maimaiga, lequel infecte les lames du Lymantria dispar. Les spores fongiques produites sur les cadavres individuels des lames tuCes par 1'E. maimaiga peuvent inclure des conidies propulstes de la surface du cadavre, des spores de repos (azygospores) ?i I'intCrieur du cadavre, ou les deux types de spores. Le facteur individuel qui exerce le plus fort impact sur le type de spores produites est 1'2ge de l'hbte; au second instar, les spores de repos sont virtuellement absentes, independamment de la temperature, alors que les cadavres de cinquikme instar contiennent plus frCquemment des spores de repos aux temptratures les plus ClevCes. Cependant, la production des conidies augmente aux basses temperatures. La photopCriode est le seul facteur CtudiC qui n'affecte pas significativement le type de spore produites. La production de spores de repos est ntgativement associCe avec le cycle de mue; les cadavres des lames qui ont muC, ou ont montrC des signes de prBmue au cours de la pCriode entre l'infection et la mort, contiennent moins de spores de repos. Une augmentation de la dose fongique induit la formation de spores de repos plus nombreuses tout comme les passages sCrits extensifs, qui entrainent simultankment une diminution de la formation des conidies. Les isolats fongiques varient quant au type de spores produites, un moindre nombre de cadavres de lames tuCes par l'isolat le moins virulent produisant des conidies. Les resultats de cette Ctude supportent l'hypothbse que 1'Ctat du pathogbne fongique aussi bien que le milieu ambiant contribuent au type de spores produites. Mots clds : sporulation fongique, spores de repos, azygospores, Entomophthorales, Entomophaga maimaiga, lutte biologique. [Traduit par la rCdaction] Received May 27, 1995. A.E. Hajek. Department of Entomology, Cornell University, Comstock Hall, Ithaca, NY 14853-0901, U.S.A. M. Shimazu.' USDA, ARS, Plant Protection Research Unit, U.S. Plant Soil and Nutrition Lab, Ithaca, NY 14853, U.S.A. ' Present address: Forestry and Forest Products Research Institute, P.O. Box 16, Tsukuba Norin Kenkyu Danchi-nai, Ibaraki 305, Japan. Introduction The Asian species Entomophaga maimaiga Humber, Shimazu & Soper is a virulent pathogen of the gypsy moth Lymantria dispar (L.) (Soper et al. 1988). This fungus was first found in North America in 1989 and since then it has spread rapidly, causing epizootics every year (Hajek et al. 1995). Because of the ability of E. maimaiga to cause abundant infections in low density populations of this outbreak insect, a large effort Can. J. Bot. 74: 708-715 (1996). Printed in Canada 1 ImprimC au Canada Can. J. Bot. Downloaded from www.nrcresearchpress.com by Harbin Industrial University on 06/06/13 For personal use only.