RESUMEN

British Columbia (BC) is the lead producer of sweet cherries in Canada with more than 2,000 ha in production and a farm gate value of over CAD$100 million annually. Since 2010, an outbreak of little cherry disease caused by Little cherry virus 1 (LChV1) and Little cherry virus 2 (LChV2), as well as X-disease (XD) caused by 'Candidatus Phytoplasma pruni' has caused significant economic losses in neighboring Washington State (WA), USA. LChV1 and LChV2 have long been known to occur in BC (Theilmann et al. 2002); however, 'Ca. P. pruni' has not yet been reported in BC. Due to its geographical proximity to WA State, the BC cherry industry expressed significant concerns about the possible presence of the phytoplasma in cherry orchards. Accordingly, the main objective of this study was to survey cherry orchards to determine whether 'Ca. P. pruni' was present in symptomatic trees in BC. A total of 118 samples of leaves and fruit stems from individual symptomatic trees were collected prior to harvest from nine cherry orchards and one nectarine orchard in the Okanagan and Similkameen Valleys in BC. Characteristic symptoms included small and misshapen fruit with poor color development. Samples were submitted to AGNEMA, LLC (Pasco, WA) for testing using qPCR TaqMan assays for LChV1 (Katsiani et al. 2018), LChV2 (Shires et al. 2022) and 'Ca. P. pruni' (Kogej et al. 2020). Test results showed 21 samples (17.8%) from three cherry orchards positive for LChV2 and 2 samples (1.7%) from one cherry orchard positive for 'Ca. P. pruni'. In order to confirm the identification of 'Ca. P. pruni', part of the 16S ribosomal RNA gene was amplified by nested PCR using the P1/P7 followed by R16F2n/R2 primer sets (Gundersen and Lee 1996) and Sanger sequenced. BC-XD-Pa-1 (GenBank Acc. No. OR539920) and BC-XD-Pa-2 (OR537699) were identical to one another and showed 99.92% identity to the 'Ca. P. pruni' reference strain CX-95 (JQ044397). Analysis using iPhyClassifier (Zhou et al. 2009) indicated that they were 16SrIII-A strains. Interestingly, the two partial 16S sequences showed 100% nucleotide identity to strain 10324 (MH810016) and others from WA. For additional confirmation, partial secA (Hodgetts et al. 2008) and secY (Lee et al. 2010) translocases were amplified and sequenced. As with the 16S sequences, secY sequences (OR542980, OR542981) showed 99.92% nucleotide identity to strain CX-95 (JQ268249), and 100% to strain 10324 (MH810035). The secA sequences (OR542978, OR542979) had nucleotide identities of 99.77% to strain CX (MW547067), and 100% to the Green Valley strain from California (EU168733). Accordingly, 'Ca. P. Pruni' was confirmed to be present in sweet cherry samples from BC. 'Ca. P. Pruni'-related strains have been previously reported to occur in Canada in commercial poinsettias (Euphorbia pulcherrima) (Arocha-Rosete et al. 2021). To our knowledge, this is the first report of 'Ca. P. Pruni' in sweet cherry in Canada. Due to the important economic value of sweet cherries in BC, these findings are highly significant and represent the first steps towards the development of a surveillance system for early detection of XD, and consequent implementation of management strategies, including vector control. As required by federal and provincial regulations, cherry trees infected with LChV2 and 'Ca. P. Pruni' found in the survey were removed by the growers.

RESUMEN

Two species of larval parasitoids of the globally invasive fruit pest, Drosophila suzukii (Diptera: Drosophilidae), Leptopilina japonica, and Ganaspis brasiliensis (both Hymenoptera: Figitidae), were detected in British Columbia, Canada in 2016 and 2019, respectively. Both are presumed to have been unintentionally introduced from Asia; however, the extent of their establishment across different habitats with diverse host plants used by D. suzukii was unclear. In addition, there was no knowledge of the temporal dynamics of parasitism of D. suzukii by these two parasitoids. To address these gaps, we repeatedly sampled the fruits of known host plants of D. suzukii over the entire 2020 growing season in British Columbia. We documented the presence of L. japonica and G. brasiliensis and estimated the apparent percentage of D. suzukii parasitized among host plant species. Across a large region of southwestern British Columbia, both L. japonica and G. brasiliensis were found to be very common across a variety of mostly unmanaged habitats over the entire course of the season (May-October) in the fruits of most host plants known to host D. suzukii larvae. Parasitism of D. suzukii was variable (0-66% percent parasitism) and appeared to be time-structured. Our study demonstrates that the close association between the two larval parasitoids and D. suzukii that exists in Asia has evidently been reconstructed in North America, resulting in the highest parasitism levels of D. suzukii yet recorded outside of its area of origin.

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RESUMEN

Spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), was monitored from 2010 to 2014 in 314-828 sites located in interior fruit-growing regions of OR and WA, United States, and BC, Canada, using traps baited with apple cider vinegar or sugar-water-yeast. Seasonal population dynamics and sex ratios were summarized for berry, cherry, stone fruit, grape, non-crop host plants, non-host sites, and for conventional IPM, certified organic, backyard, and feral sites, by region and year. Overwintering was detected in all regions and years, despite winter temperatures below -17°C. A spatial analysis was conducted using a Geographic Information System (GIS), daily weather data, geomorphometric measures of terrain, distance to water, and other variables, at each site. Overwintering success at a site, measured as Julian week of first capture of D. suzukii, was significantly related (R2 = 0.49) in cherry habitats to year, agronomic treatment, and number of winter days with temperatures >-5°C. In berry, cherry, stone fruit and grape habitats, 2011-2014, it was significantly related (R2 = 0.42) to year, agronomic treatment, the logarithm of peak population of D. suzukii in the prior autumn, latitude, elevation, and topographic wetness index. The results show that D. suzukii has adapted to exploit a succession of irrigated crops and feral habitats in mixed landscapes of a semi-arid region with cold winters and hot dry summers, and are shaping strategies for pest management and for biological control.

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It has been hypothesized that the success of a biological control introduction is, in part, dependent on the ability of the control agent to become established in its new environment or to its new population of hosts through local adaptation. Despite this, few studies have investigated the influence of the recent coevolutionary history of pest species and natural enemies on the efficacy of biological control agents, especially for agents that are mass-reared for release in agriculture. We investigate the evolutionary potential of a biological control agent Aphidius ervi to adapt to a key pest species, the foxglove aphid Aulacorthum solani, through components essential to the evolution of parasitoid virulence. We explored (1) the influence of genetic variation from natural source populations on the ability to parasitize natal and non-natal host species; (2) the heritability of key traits related to parasitoid fitness; and (3) the efficacy of parasitoid host-selection lines in a greenhouse system. Source populations maintained genetic variation in the ability to utilize natal and non-natal host species; however, only some of the traits sampled suggested local adaptation of parasitoid populations. The ability to parasitize a host was found to be genetically determined and strongly heritable, irrespective of host species. The greenhouse study demonstrated the potential of parasitoid selection lines to substantially increase performance of parasitoids for target pest species. This research provides insight into novel techniques that can be used to increase the quality of biological control agents through the development of lines of natural enemies adapted to particular pest species.

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