FORMATION AND GERMINATION OF ENTOMPHAGA MAIMAIGA AZYGOSPORES

Authors: HAJEK, ANN - CORNELL UNIVERSITY; Humber, Richard

Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: ENTOMOPHAGA MAIMAIGA is an important fungal pathogen of gypsy moth (LYMANTRIA DISPAR; GM) larvae. Under severe disease situations, this fungus can reduce GM populations as much as 85%. The fungus survives both the winter and the absence of suitable hosts in a thick-walled (resting) spore state. Such resting spores have been used effectively to spread the fungus to GM-infested sites in Michigan and elsewhere where the pathogen has been absent. This study focused on the conditions affecting the development, dormancy, and germination of the resting spore. We found that resting spores form and mature quickly after the death of affected hosts, that naturally occurring resting spores remain dormant (metabolically inactive) for some 9 months after they form, and that spores can be activated to germinate within 2 days of the restoration of suitable conditions after the dormant period. Resting spores do not begin to germinate naturally in the field until the year's host population of GM is well established. This information improves the likelihood of being able to manipulate resting spores of E. MAIMAIGA in the laboratory to improve the chance of obtaining successful field introductions at potentially earlier times in a season than the fungus would normally be active, and to obtain higher levels of control of targetted GM populations.

Technical Abstract: Azygospores (resting spores) of the gypsy moth fungal pathogen ENTOMOPHAGA MAIMAIGA are produced in abundance during late spring and early summer in late instar gypsy moth larvae (LYMANTRIA DISPAR). Hyphal bodies are present in the hemolymph when the hosts die. Azygo- spores subsequently form, each from an individual hyphal body. Forma- tion of azygospores occurs asynchronously; by 5 days after host death > 60% of fungal cells had matured to the final double-walled resting state. Azygospores undergo constitutive dormancy and, under field conditions, will not germinate for approximately 9 months after pro- duction. Azygospores do not require nutrients to germinate. Germina- tion of field-collected resting spores under laboratory conditions began > 2 days after transfer from the field to the laboratory. Higher levels of germination were associated with longer photoperiods, and 71.8 or 72% germination occurred at 15 or 20 C, respectively, after 16 days. During 1994 and 1995, resting spores began causing infections in experimental larvae in early May, about 1-2 weeks prior to gypsy moth egg hatch and ceased causing infections in mid-late June, when late instars were present. This latter timing is a change from previ- ously reported information. Bioassays investigating resting spores activity determined that during 1994, once resting spores began germi- nating in the field, levels of infection were positively associated with soil moisture (p < 0.05).