Infection, course of disease and effects of Canningia tomici in Tomicus piniperda and Tomicus minor (Coleoptera: Curculionidae)

Background and purpose. The pine shoot beetles Tomicus piniperda and Tomicus minor are secondary tree pests attacking weakened Pinus sylvestris and Pinus nigra. Outbreaks occasionally occur, causing considerable economic damage. The microsporidian pathogen Canningia tomici infects T. piniperda as its principal host. Bioassays were used to study the infectivity, vertical transmission, and effects on survival and fecundity of C. tomici on the two beetle species. Materials and methods. Field collected beetles from several locations in Austria (Lower Austria, Burgenland and Styria), Finland (Hyytiälä), Poland (Sękocin), the Czech Republic (Stará Boleslav), and Croatia (Korenica) (3410 T. piniperda, 413 T. minor) were dissected and evaluated for the presence of C. tomici. Uninfected beetles to be used for infection experiments were only collected from the Austrian sites. Canningia tomici spores were extracted from the infected organs of T. piniperda by dissection and tissues were homogenized in a glass tissue grinder. Microsporidian spores were suspended in water and were counted in a hemocytometer. Infection experiments began with T. piniperda and T. minor as soon as parental beetles were available in the field in spring, or filial beetles emerged from infested log sections in the laboratory. To test the effect of maturation feeding on infection success, filial beetles of both species were either inoculated immediately after emergence from a log section, or were allowed to feed on P. sylvestris twigs for several days before inoculation. Filial beetles were held in Petri dishes containing P. sylvestris twigs at 8°C and long-day conditions (16L:8D) during the maturation feeding period. Afterwards, they were removed from the twigs, starved for 24 hours, and then inoculated with a 1-μl spore suspension or water. All beetles were checked daily until death, dissected and inspected for the presence of C. tomici spores. All data were analyzed with the software program R. Frequency data sets were compared using Chi-square analysis. Multiple comparisons were controlled for Type I errors using the Bonferroni method. The datasets of multiple dependent scale variables were analysed using the LM multivariate procedure, testing the effects of the following factors: year, temperature, inoculation, successful infection, maturation feeding, and sex. Results. The overall prevalence of C. tomici in T. piniperda was 1.9%, with significantly more female T. piniperda infected. No infections were observed in T. minor. After feeding spore suspensions to parental and filial T. piniperda and T. minor, between 0% and 67% of the beetles were successfully infected, regardless of the incubation temperature or sex of the beetles. Survival time was significantly influenced by the incubation temperature and successful infection; in filial beetles the maturation feeding DÖRTE GOERTZ1 MILAN PERNEK2 UWE HAENDEL1 BERNHARD KOHLMAYR3 RUDOLF WEGENSTEINER1 1 University of Natural Resources and Applied Life Sciences, BOKU Vienna, Department of Forest and Soil Sciences, Gregor-Mendel-Straße 33, A-1180 Vienna, Austria. 2 Croatian Forest Research Institute, Cvjetno naselje 41, 41250 Jastrebarsko, Croatia. 3 Leopoldine-Schlinger-Gasse 4/10, A-1020 Vienna, Austria. Correspondence: Milan Pernek E-mail: [email protected]