- Email: [email protected]
Catenaria auxiliaris (Chytridiomycetes: Blastocladiales) identified in a larva of Scolytus scolytus (Coleoptera: Scolytidae)
JOURNAL
OF INVERTEBRATE
PATHOLOGY
32,
392-393
(1978)
Catenaria auxiliaris (Chytridiomycetes: Blastocladiales) Identified Larva of Scolytus scolytus (Coleoptera: Scolytidae)
elm bark beetles and larvae during the previous summer. The particular bark sample in which the infected larva was found was fairly wet and in direct contact with the soil. Much of the larva had disintegrated to reveal a pale pink mass of spores. Microscopical examination revealed a small proportion of pale brown reticulate spores or sporangia and almost colorless smooth-walled sprangiumlike structures (Figs. lA,B). These were similar in size (20-70 pm) and appearance to the resting spores and precursor sporangia of Catenaria auxiliaris. The one point of difference was the presence of distinct spines on some of the precursor sporangia (Fig. IC). On discussing the matter with Dr. Neil Wilding (Rothamsted Experimental Station, Harpenden, England), he mentioned that he had seen preparations of resting spores of Entomophthora muscae from wheat bulb fly, Leptohylemyia coarctata, in which some of the spores bore setae apparently originating from the host cuticle. Examination of the cuticle of Scolytus larvae showed that it bore spines identical with those in Figure 1C. Evidently, parts of the larval cuticle had not disintegrated but had become closely attached to adjacent precursor sporangia. It is not certain whether the fungus had actually infected a healthy Scolytus larva, or whether it had grown saprophytically on moribund tissues. Growth has been noted by H. T. Tribe (lot. cit.) on degenerating nematode tissues, although no growth was obtained by inoculating zoospores onto agar. It is hoped that increased awareness of this fungus may lead to clarification as to whether this was an isolated occurrence on an insect host, or whether the fungus regularly, if sporadically, occurs on insects as well as parasitises cyst-nematodes. The common species of insect pathogenic fungi
Catenaria auxiliaris (formerly Tarichium auxiliare) is a fungal pathogen of cystnematodes of the genus Heterodera (H. T. Tribe, Trans. Brit. Mycol. Sot. 69, 367-376,
1977). So far, it has been found in two species, Heterodera schachtii, the sugar beet cyst-nematode (H. T. Tribe, lot. cit.) and Heterodera avenae, the cereal cyst-nematode (B. R. Kerry & D. H. Crump, Nematologica 23, 193-201, 1977). Infection of the female nematode is initiated by motile zoospores, and a rhizomycelium, consisting of strings of swellings, develops inside the cyst-nematode. Each swelling then converts into a typically globose or subglobose precursor sporangium, usually 20-50 ,um in diameter, which matures either into a resting sporangium or, less frequently, into a zoosporangium. A single resting spore is formed inside the resting sporangium, either lying loosely or fused with the sporangial wall. This resting spore has a reticulate wall of highly characteristic appearance, which closely resembles that of chlamydospores of certain smut fungi, notably Tilletia contraversa and Tilletia curies, but cannot be confused with spores of other fungi. Catenaria auxiliaris is therefore easy to recognize, but despite this, there seem to be no previous records of its being found outside of cyst-nematodes. This note reports its identification in a single late-instar larva of Scolytus scolytus, the large elm bark beetle and most important vector of Dutch elm disease in Britain. The fungus was found, on May 27, 1976, at Cambridge, England, while one of us (J. W.D.) was checking mortality of elm bark beetle larvae in elm logs. These logs formed part of a field experiment concerned with other fungal pathogens of elm bark beetles. They had been in the field for 12 months, having been experimentally infested with 0022-2011/78/0323-0392$01.00/O Copyright 0 1978 by Academic Press, Inc. A8 rights of reproduction in any form reserved.
in a
392
393
NOTES
FIG. 1. Catenariu auxiliaris from larva of Scolytus scolytus. (A) Precursor and resting sporangia in me focus. Unstained in lactophenol. x 500. (B) Two resting sporangia in upper focus showing the reticulate wall of the spore. Unstained in lactophenol. Phase. x 800. (C) Precursor sporangia bearing spines from the latrval cuticle. Stained with trypan blue in lactophenol. x 500.
are not parasites of cyst-nematodes (H. T. Tribe, Biol. Rev. 52, 477-507, 1977) and it is therefore of great interest to learn of the host range of cyst-nematode pathogens. KEY
WORDS:
Catenaria auxiliaris; Scaly-
tus scolytus ; fungus; nematode.
J. W.
DOBEA
H. T. TRIBE Department University Pembroke
of Applied of Cambridge
Biology
Street
CambridgeCB~3*x, &&,d Received
February
23, 1978
LSKI
OF INVERTEBRATE
PATHOLOGY
32,
392-393
(1978)
Catenaria auxiliaris (Chytridiomycetes: Blastocladiales) Identified Larva of Scolytus scolytus (Coleoptera: Scolytidae)
elm bark beetles and larvae during the previous summer. The particular bark sample in which the infected larva was found was fairly wet and in direct contact with the soil. Much of the larva had disintegrated to reveal a pale pink mass of spores. Microscopical examination revealed a small proportion of pale brown reticulate spores or sporangia and almost colorless smooth-walled sprangiumlike structures (Figs. lA,B). These were similar in size (20-70 pm) and appearance to the resting spores and precursor sporangia of Catenaria auxiliaris. The one point of difference was the presence of distinct spines on some of the precursor sporangia (Fig. IC). On discussing the matter with Dr. Neil Wilding (Rothamsted Experimental Station, Harpenden, England), he mentioned that he had seen preparations of resting spores of Entomophthora muscae from wheat bulb fly, Leptohylemyia coarctata, in which some of the spores bore setae apparently originating from the host cuticle. Examination of the cuticle of Scolytus larvae showed that it bore spines identical with those in Figure 1C. Evidently, parts of the larval cuticle had not disintegrated but had become closely attached to adjacent precursor sporangia. It is not certain whether the fungus had actually infected a healthy Scolytus larva, or whether it had grown saprophytically on moribund tissues. Growth has been noted by H. T. Tribe (lot. cit.) on degenerating nematode tissues, although no growth was obtained by inoculating zoospores onto agar. It is hoped that increased awareness of this fungus may lead to clarification as to whether this was an isolated occurrence on an insect host, or whether the fungus regularly, if sporadically, occurs on insects as well as parasitises cyst-nematodes. The common species of insect pathogenic fungi
Catenaria auxiliaris (formerly Tarichium auxiliare) is a fungal pathogen of cystnematodes of the genus Heterodera (H. T. Tribe, Trans. Brit. Mycol. Sot. 69, 367-376,
1977). So far, it has been found in two species, Heterodera schachtii, the sugar beet cyst-nematode (H. T. Tribe, lot. cit.) and Heterodera avenae, the cereal cyst-nematode (B. R. Kerry & D. H. Crump, Nematologica 23, 193-201, 1977). Infection of the female nematode is initiated by motile zoospores, and a rhizomycelium, consisting of strings of swellings, develops inside the cyst-nematode. Each swelling then converts into a typically globose or subglobose precursor sporangium, usually 20-50 ,um in diameter, which matures either into a resting sporangium or, less frequently, into a zoosporangium. A single resting spore is formed inside the resting sporangium, either lying loosely or fused with the sporangial wall. This resting spore has a reticulate wall of highly characteristic appearance, which closely resembles that of chlamydospores of certain smut fungi, notably Tilletia contraversa and Tilletia curies, but cannot be confused with spores of other fungi. Catenaria auxiliaris is therefore easy to recognize, but despite this, there seem to be no previous records of its being found outside of cyst-nematodes. This note reports its identification in a single late-instar larva of Scolytus scolytus, the large elm bark beetle and most important vector of Dutch elm disease in Britain. The fungus was found, on May 27, 1976, at Cambridge, England, while one of us (J. W.D.) was checking mortality of elm bark beetle larvae in elm logs. These logs formed part of a field experiment concerned with other fungal pathogens of elm bark beetles. They had been in the field for 12 months, having been experimentally infested with 0022-2011/78/0323-0392$01.00/O Copyright 0 1978 by Academic Press, Inc. A8 rights of reproduction in any form reserved.
in a
392
393
NOTES
FIG. 1. Catenariu auxiliaris from larva of Scolytus scolytus. (A) Precursor and resting sporangia in me focus. Unstained in lactophenol. x 500. (B) Two resting sporangia in upper focus showing the reticulate wall of the spore. Unstained in lactophenol. Phase. x 800. (C) Precursor sporangia bearing spines from the latrval cuticle. Stained with trypan blue in lactophenol. x 500.
are not parasites of cyst-nematodes (H. T. Tribe, Biol. Rev. 52, 477-507, 1977) and it is therefore of great interest to learn of the host range of cyst-nematode pathogens. KEY
WORDS:
Catenaria auxiliaris; Scaly-
tus scolytus ; fungus; nematode.
J. W.
DOBEA
H. T. TRIBE Department University Pembroke
of Applied of Cambridge
Biology
Street
CambridgeCB~3*x, &&,d Received
February
23, 1978
LSKI