Progress 10/01/03 to 09/30/06
Outputs
To better assess the vector potential of insects we have found associated with Sirococcus clavigignenti-juglandacearum (Scj) on butternut (Juglans cinerea) in Vermont, we looked more closely at the viability and infectivity of Scj conidia carried externally and internally. Our laboratory studies show that Scj conidia remain viable on exoskeletons of A. macula, E. parochus, and Glischrochilus sanguinolentus (Nitidulidae) for at least 16 days; however, viability decreases with time. Examination of fecal pellets deposited over time shows that conidia remain viable in the digestive tract and fecal pellets of A. macula for up to 48 hours and of E. parochus for up to 24 hours. To determine if conidia carried by beetles remain infective to butternut, butternut curculios, artificially infested with Scj conidia, were caged with butternut seedlings, until one or more feeding or oviposition wounds were created. The fungus was re-isolated from wound areas after 4-5 weeks. Fecal
pellets from A. macula, artificially fed conidia of Scj, were also used to inoculate butternut seedlings. Again, Scj was re-isolated from inoculation areas after 4-5 weeks. Previous research on longevity of conidia of Scj suggests that airborne spores remain viable short durations after dissemination. In contrast, our studies show that conidia remain viable on insect exoskeletons for relatively long periods of time. Each of these beetle species is capable of vectoring conidia of Scj in some capacity. As far as we know, A. macula and E. parochus do not subsist on or wound living, healthy butternut tissues in any way. However, the insects carry high numbers of spores of Scj externally and internally and may inadvertently infect living butternut bark as they crawl to dead and dying stems and branches to which they are attracted. Therefore, we consider A. macula and E. parochus casual vectors of Scj. Although the butternut curculio only occasionally carries low levels of conidia of Scj,
our seedling inoculation study shows that the insect is capable of transferring conidia from its exoskeleton to the feeding and oviposition wounds it creates in new shoots of butternut. Because the curculio is not attracted to dead butternut tissue where Scj sporulates, we consider this insect a limited potential vector of Scj but an effective predisposing/wounding agent. Species of nitidulids are well known vectors of other disease-causing fungi, such as the oak wilt fungus Ceratocystis fagacearum. We have noted them crawling into oozing butternut cankers and fresh curculio wounds. Although we have not observed nitidulids visiting sticky sporulating hyphal peg areas, we know nitidulids are attracted to such substrates and carry low levels of Scj conidia. Therefore, we believe they have great potential to disseminate conidia to curculio wounds or other suitable infection courts. It seems likely that each of these insects is playing a role, depending on its life cycle, in the spread of
Scj conidia within and between butternut trees.
Impacts
We now have evidence to show how closely related certain insect species are to the suspected exotic fungus causing butternut canker. These beetles are more than likely helping to disperse the fungus within a tree and between trees. Management of this disease may include reducing certain insect populations within a stand by removing dead material on the ground that is attractive to both the fungus and the beetles.
Publications
- Halik, S., and Bergdahl, D.R. 2006. Observations on the natural history, development, range, and future of Eubulus parochus (Herbst) (Coleoptera: Curculionidae). The Coleopterists Bulletin 60(4):325-332.
- Stewart, J.E., Halik S., and Bergdahl, D.R. 2004. Viability of Sirococcus clavigignenti-juglandacearum conidia on exoskeletons of three coleopteran species. Plant Disease 88:1085-1091.
- Halik, S., Stewart, J.E., and Bergdahl, D. R. 2003. Comparison of butternut curculio wounds and artificial wounds as infection courts of Sirococcus clavigignenti-juglandacearum on butternut seedlings. Phytopathology 93(6):S133.
- Stewart, J.E., Halik S., and Bergdahl, D.R. 2003. Conidiospores of the butternut canker fungus carried on the exoskeletons of three different potential beetle vectors. Phytopathology 93(6):S135.
- Stewart, J.E., Halik, S., and Bergdahl, D.R. 2003. Viability of conidiospores of the butternut canker fungus on potential beetle vectors. Annual Report of the Northern Nut Growers Association 94:1-8.
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Progress 10/01/04 to 09/30/05
Outputs
Conidia of Sirococcus clavigignenti-juglandacearum (SCJ), the fungus causing butternut canker, are carried and consumed by the beetles Astylopsis macula and Eubulus parochus. Conidia remain viable on exoskeletons, but viability is unknown after passage through the beetles digestive tracts. In 2004 and 2005, we collected 30-40 each of A. macula and E. parochus and fed all but 10 of each sporulating SCJ on butternut twigs. Fecal pellets were collected up to 96 h after feeding. Pellets were dissolved in sterile distilled water and streaked on malt extract agar to observe growth of SCJ and percent germination of conidia. Remaining pellet solution was stained with aniline blue and conidia counted using a hemacytometer. Numbers of conidia ranged from 0 to 533,750 and 0 to 86,250 in pellets of A. macula and E. parochus, respectively. Viable conidia were deposited by A. macula for up to 48 h and by E. parochus for up to 24 h. Germination of conidia from E. parochus pellets
remained above 90% for at least 6 h. Fecal pellets from A. macula were used to inoculate butternut seedlings, resulting in infections and confirming another means of spore dissemination for SCJ.
Impacts
We now have evidence to show how closely related certain insect species are to the suspected exotic fungus causing butternut canker. These beetles are more than likely helping to disperse the fungus within a tree and between trees. Management of this disease may include reducing certain insect populations within a stand by removing dead material on the ground that is attractive to both the fungus and the beetles.
Publications
- Stewart, J.E., Halik, S., and Bergdahl, D.R. 2004. Viability of Sirococcus clavigignenti-juglandacearum conidia on exoskeletons of three coleopteran species. Plant Disease 88:1085-1091.
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Progress 10/01/03 to 09/30/04
Outputs
We have found that Eubulus parochus and Astylopsis macula (two potential beetle vectors of Sirococcus clavigignenti-juglandacearum, the butternut canker fungus) often feed on the fruiting bodies and spores of the fungus in the field. To determine how long spores remain viable in the beetles digestive tracts, we collected E. parochus and A. macula from butternut trees and allowed them to feed on spores of the fungus in the lab for 2 hours. At time intervals ranging from 2 to 120 hours after feeding, we collected fecal pellets of the beetles and soaked the pellets in water. Spore numbers were counted microscopically, and spore viability was measured by streaking soaked pellets on malt agar media and determining percent spore germination. For both insects, spores were found in pellets up to 48 hours after consumption of the fungus, and spores remained viable for up to 24 hours. We also inoculated 4-month-old butternut seedlings with fecal pellets deposited 2, 4, and 6
hours after feeding by A. macula. For each time interval, up to 8 of the 16 seedlings inoculated became infected. Thus, in addition to spores remaining viable on the exoskeletons of these beetles, it appears that spores also remain viable and infective when consumed and passed through the digestive tracts of these potential insect vectors. Although these two beetle species probably do not feed on healthy butternut tissue, they may inadvertently deposit fecal pellets, containing viable, infective spores, on healthy tissue while crawling to dead and dying branches to which they are attracted for feeding and oviposition in the crowns of living butternut trees.
Impacts
In addition to carrying spores externally, potential insect vectors of the butternut canker fungus are also feeding on the fungus and depositing viable spores in fecal pellets. This may increase the chances of fungal survival and likelihood of infecting a new host tree or new site on a host tree. Management of this disease may include reducing insect populations to reduce spore dissemination.
Publications
- Stewart, J.E., Halik S., and Bergdahl, D.R. 2004. Viability of Sirococcus clavigignenti-juglandacearum conidia on exoskeletons of three coleopteran species. Plant Disease 88:1085-1091.
- Jacobs, K., Bergdahl, D.R., Halik, S., Wingfield, M.J., Seifert, K.A., Bright, D.E., and Wingfield, B.D. 2004. Leptographium wingfieldii introduced to North America and found associated with exotic Tomicus piniperda and native bark beetles. Mycological Research 118:411-418.
- Pfister, S.E., Halik, S., and Bergdahl, D.R. 2004. Effect of temperature on Thekopsora minima urediniospores and uredinia. Plant Disease 88:359-362
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Progress 10/01/02 to 09/30/03
Outputs
We have found that potential beetle vectors of Sirococcus clavigignenti-juglandacearum (the butternut canker fungus) often feed on the fruiting bodies and spores of the fungus in the field. To determine how long spores will remain viable in digestive tracts of two potential beetle vectors, we collected Eubulus parochus and Astylopsis macula from diseased butternut trees and allowed them to feed on spores of the fungus in the lab for 24 hours. At time intervals ranging from 2 hours to 120 hours, we collected fecal pellets of the beetles and soaked the pellets in water. Spore numbers were counted microscopically, and viability of the spores was measured by streaking the water on malt agar media and determining percent spore germination. For both insects, spores were found in pellets up to 48 hours after consumption of the fungus and spores remained viable for up to 24 hours. In addition to spores remaining viable on the exoskeletons of these beetles, it appears that
spores also remain viable when consumed and passed through their digestive tracts. To potentially increase the number of hours that spores are deposited in pellets, we will repeat the study allowing beetles to feed for shorter lengths of time. Prior to the study, beetles were rinsed with water to remove field spores and debris; and rinse water was used to inoculate butternut seedlings in a greenhouse. The fungus was re-isolated from 1% of the 96 seedlings inoculated, probably comparable to natural infection rates in the field.
Impacts
In addition to carrying spores externally, potential insect vectors of the butternut canker fungus are also feeding on the fungus and depositing viable spores in fecal pellets. This may increase the chances of fungal survival and likelihood of infecting a new host tree or new site on a host tree. Management of this disease may include reducing insect populations to reduce spore dissemination.
Publications
- Halik, S. and Bergdahl, D.R. 2002. The butternut curculio as a vector of the butternut canker fungus. Annual Report of the Northern Nut Growers Association 93.
- Halik, S., Stewart, J.E., and Bergdahl, D. R. 2003. Comparison of butternut curculio wounds and artificial wounds as infection courts of Sirococcus clavigignenti-juglandacearum on butternut seedlings. Phytopathology 93(6):S133.
- Stewart, J.E., Halik S., and Bergdahl, D.R. 2003. Conidiospores of the butternut canker fungus carried on the exoskeletons of three different potential beetle vectors. Phytopathology 93(6):S135.
- Stewart, J.E., Halik, S., and Bergdahl, D.R. 2003. Viability of conidiospores of the butternut canker fungus on potential beetle vectors. Annual Report of the Northern Nut Growers Association 94.
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