The host range of the eriophyid mite Aceria vitalbae, a biological control agent for Clematis vitalba. Host range tests were carried out in Serbia for Landcare Research by Dr Biljana Vidovic of the University of Belgrade (Vidovic, 2016). Summary The risk posed by Aceria vitalbae to plants in New Zealand, the target range of the biological control agent, was assessed by laboratory experiments. All eriophyid mites are more or less host specific. Testing the ability of Aceria vitalbae to form a viable population when transferred to species of the genus Clematis was considered sufficient to assess the risks to the New Zealand flora. Mites transferred to seedlings of Clematis vitalba controls established easily but there was no establishment on seedlings of Clematis species native to New Zealand. This is strong confirmation that A. vitalbae is host specific. Further tests on the remaining native Clematis species and several representative ornamental Clematis species will be completed in 2017. Test plant selection The genus Clematis belongs to the sub family Ranunculoideae of the family Ranunculaceae. There are 9 native Clematis species in New Zealand. Four other genera in the subfamily are represented in the native flora. Most have only one or two native species but the genus Ranunculus has approximately 40 species. The phylogenetic study of Cai et al. (2009) recognised separate clades for the Clematis Anemone and Ranunculus Myosurus groups within the Ranunculoideae. Other New Zealand genera were less closely related to Clematis, (although the genus Ceratocephalus was not treated). Eriophyid mites are regarded as highly host specific (Skoracka et al., 2010) and have been used in many biological control programmes against weeds (Vasquez et al., 2015). Hong et al. reported that approximately 88% of eriophyid mites in China are found on a single plant species and another 10% on two species within the same genus. Only around 2% were found on plants belonging to more than one genus (Hong et al., 2001). Gall forming species within the eriophyids, such as Aceria vitalbae, are likely to be even more specific. Given the host use patterns of eriophyid mites, it was concluded that inability to form a population on Clematis species other than C. vitalba would be sufficient evidence that A. vitalbae would not attack species of other genera on release in New Zealand.
Xie et al. (2011) researched the phylogenetic relationships between species of Clematis and identified 10 recognisable clades. They place the Australasian species (with only one New Zealand species represented) in a clade far distant from the clade containing the European Clematis species, including C. vitalba. Nevertheless, all but one of the New Zealand native species were selected for testing. C. cunninghamii could not be sourced and was not tested. Clematis marmoraria is an unusual, reduced species found in limited alpine areas of the Arthur Range in NW Nelson. It was only available as a hybrid with C. petrei. Garden Industry New Zealand (now New Zealand Plant Producers Incorporated) was consulted, and growers recommended ten commercial Clematis species that might be tested. Overall, seven Clematis species that are exotic to New Zealand were selected to represent commercial interest and to provide representative coverage across the 10 clades described by Xie et al. (2011). Methods Five native Clematis species were tested in 2016, and tests on the following 10 species are in progress: C. marmoraria x petriei, C. marata, C. forsteri (native species), C. montana, C. patens, C. terniflora, C. stans, C. viticella, C. recta, and C. integrifolia (exotic) Seedlings of the first Clematis spp. sent from New Zealand arrived in Belgrade in good condition on October 10, 2015 (Fig.1). There were a total of 110 seedlings of which: 1) Clematis foetida 28 pieces 2) Clematis afoliata 22 pieces 3) Clematis paniculata 19 pieces 4) Clematis quadribracteolata 30 pieces 5) Clematis petriei 11 pieces Seedlings were planted in pots with a sterile substrate. The plants were grown in controlled conditions (temperature: 22 0 C ±2; the ratio of day and night: 16 hours light/8 hours darkness). (Fig. 2)
C. foetida C.afoliata C. paniculata C. quadribracteolata C.petriei Figure 1. Test seedlings received from New Zealand Figure 2. Growing conditions Tests were carried out with a population of Aceria vitalbae collected from Clematis vitalba near Belgrade, Serbia. Mites were transferred to small plants of C. vitalba and maintained in laboratory conditions. These populations of mites were used for host specificity tests (Fig. 3). Tests were initiated on February 17 22, 2016. Mites overwinter in the buds of C. vitalba as deutogyne females (an inactive form, without feeding and reproduction) and became active at this time.
Figure 3. A Clematis vitalba plant supplying mites for tests. Individual mites were transferred using thin needles under the stereo microscope. Twenty mites were transferred onto 10 plants of each of the five Clematis spp. from New Zealand. Mites were also transferred to 10 Clematis vitalba plants from Serbia as controls. After 60 days, all plants were checked under the stereomicroscope for the presence of mites, and the mites were then also extracted (Fig.4). Plant material was covered with a washing solution (0.2% household detergent and 2% bleach in tap water) in a large container. The resulting suspension was stirred and mites were collected using four sieves (mesh size: 850, 180, 53 and 25µm) and tap water. The sediment from sieve of 53 µm was washed into a Petri dish. Mites were counted under a stereomicroscope. Figure 4. Extraction method Results After 15 days, mites were still alive on all test plants and controls. After 30 days, mite populations continued to develop (laying eggs and producing a new generation) on all C. vitalba (Table 1). Mite colonies survived for 60 days on all C. vitalba replicates causing serious leaf deformation. No mite survival was recorded on any other test plants beyond 15 days (Fig. 6). Aceria vitalbae developed populations on Clematis vitalba only (Fig. 5).
Table 1. Survival and presence of Aceria vitalbae on Clematis species in tests over time Plant taxa No. of replicates No. of replicates attacked Estimated presence of mites after 15 days 30 days 60 days Clematis vitalba 10 10 + + + C. foetida 10 0 + C. afoliata 10 0 + C. paniculata 10 0 + C. quadribracteolata 10 0 + C. petriei 10 0 + Control without mites Control after 60 days Symptom on the leaf
Colony of the Aceria vitalbae Figure 5. Clematis vitalba The mites after extraction from the plants Clematis foetida Clematis afoliata
Clematis paniculata Clematis quadribracteolata Clematis petriei Figure 6. Base of buds, leaf and whole plants after tests. Discussion The results of host range tests completed in 2016 strongly suggest that Clematis vitalba is the only a suitable host for Aceria vitalbae. Mites severely damaged seedlings of C. vitalba but caused no effect on other Clematis species. This tentative conclusion will be confirmed with the completion of tests on the remaining New Zealand native Clematis species and a representative selection of ornamental Clematis species valued in New Zealand horticulture. These tests will be completed in June 2017. Damage by Aceria vitalbae on the leaves and vegetative buds of C. vitalba makes this mite a potentially valuable biological control agent. Damage to leaves and growing points may have a negative effect on the fitness of the host plant, especially in stressed conditions, resulting in reduced competition with other plants. References Cai, YF; Li, SW; Liu, Y; Quan, S; Chen, M; Xie, YF; Jiang, HZ; Wei, EZ; Yin, NW; Wang, L; Zhang, R; Huang, CL; He, X H; Jiang MF (2009). Molecular phylogeny of Ranunculaceae based on internal transcribed spacer elements. African Journal of Biotechnology 8: 5215 5224.
Hong, XY; Dong, HQ; Fu, YG; Cheng, LS, Oldfield, N. (2001). Relationships between eriophyoid mites and their host plants, with a case review of Eriophyoidea fauna of China. Systematic and Applied Acarology 6: 119 136. Skoracka, A.; Smith, L,; Oldfield, G.; Cristofaro, M.; Amrine, J.W.; (2010). Host plant specificity and specialization in eriophyoid mites and their importance for the use of eriophyoid mites as biocontrol agents of weeds. Experimental and Applied Acarology 51:93 113. Vasquez, C.; Colmenarez, Y.; Morales Sanches, J.; Valera, N.; Sandoval, M.F.; Balza, D. (2015). Current and potential use of phytophagous mites as biological control agents for weeds. In: Pilipavičius, V. (ed.) Weed Biology and Control. INTECH. Vidovic, B. (2016). Initial host specificity tests using Aceria vitalbae, the eriophyid mite of C. vitalba. Unpublished Report to Landcare Research, 6p. Xie, L.; Wen, J; Li, LQ. (2011). Phylogenetic analyses of Clematis (Ranunculaceae) based on sequences of nuclear ribosomal ITS and three plastid regions. Systematic Botany 36: 907 921.