Behavioural observations began with daily monitoring of the garden L. latifolius plant by ML for flowering and beetle activity from June through September 2021. First inflorescences having flowers open were tagged and then tracked. The first available pods were monitored for oviposition. Tagged pods remained on the plant until mature when they were harvested and permitted to dehisce. All remaining closed pods were opened manually two months after harvest. Seed infestation and parasitoid presence were assessed for all seeds from all tagged pods. Herbarium vouchers from both Lathyrus species were collected, for deposition in herbaria (CAN/DAO) (Fig. 3A, B).

Figure 3. 

Morphology of Lathyrus spp. and B. affinis from Québec, Canada A apex of L. latifolius stem, garden plant (45.464, −75.561) B L. sylvestris stem, pressed (45.457, −75.767) C egg of B. affinis on outer pod wall of L. sylvestris D opened pod of L. sylvestris with seed entry holes of B. affinis larvae and white inner pod wall tissue developing beneath oviposition sites E infested seed of L. sylvestris with first instar larva of B. affinis F same with second instar larvae. Scale bars: 50 mm (A, B); 0.5 mm (C); 25 mm (D); 5 mm (E, F).

Adult beetles were hand collected (i.e. not using a net) from L. sylvestris at behavioural study sites by ML in early morning. Specimens were preserved in 95% ethanol with several voucher specimens mounted. Stem tagging was not possible at the L. sylvestris roadside localities. So, randomly selected stems were used for study. Pods at varying developmental stages were examined and/or collected on several mornings from June to October. All seeds retained for rearing were stored at room temperature and examined daily for presence of emergent beetles. Maturing green to yellow seeds were opened within 24 hours of collection using a scalpel to view their contents (Fig. 5B). Mature brown seed samples, that floated when placed in water, were cracked open using a vacuum vise with exposed steel jaws. Seeds that sank in water and could not be cracked open were scored as uninfested. Additional pods were kept at 20 °C until January 2022 for further emergence of beetles or parasitoids.

Field photography was conducted by ML using an Olympus 12.5× Super Wide Optical Zoom camera. Macro photography was done using an Olympus EM5 MkII with macro lens according to subject and an Olympus T10 Ring Flash or an Olympus RFII Ring Flash for larger subjects. An Epson Perfection Scanner V550 Photo was used to document Lathyrus stems and herbarium specimens.

The external morphology and male genitalia of Canadian specimens closely matched taxon concepts of B. affinis from Brandl (1981) and Borowiec (1988). A. Delobel, and L. Borowiec also confirmed our initial identifications based on submitted photographs. Specimens identified also matched Canadian National Collection specimens identified by Anton, Natterer, and Bottimer in morphology of the pronotum, male mesotibia, and aedeagus.

We found B. affinis at the following localities in Canada: British Columbia: Vancouver, 49.2162, −123.1713, 22.VI.2021, ex. L. latifolius, B. Spencer, 4 ex; Québec: Gatineau, 45.463, −75.765, reared from L. latifolius seeds from garden, M.H.S Light, 8 ex., CNC1053109 to CNC1053117; Gatineau, 5.IX.2021, M.H.S. Light; Wakefield, 45.6466, −75.9298, reared from L. sylvestris seeds of field edge patch,15.VIII.2021, M.H.S. Light, 12 ex.; Gatineau, boul. Cité des Jeunes, 45.4544, −75.7601, mating on flowering L. sylvestris of roadside patch, 27.VI.2021, M.H.S. Light, 5 ex.; Gatineau, 45.4546, −75.7604, 27.VI.2021, M.H.S. Light, 18 ex.; Gatineau, 45.464, −75.761, reared from L. latifolius seeds from garden, 18.VIII.2021, M.H.S. Light, 1 ex.; Gatineau, 45.71, −75.7672, reared from L. sylvestris seeds of a roadside patch, 15.VIII.2021, M.H.S. Light, 5 ex.; Gatineau, 45.4551, −75.7612, reared from L. sylvestris seeds, 15.VIII.2021, M.H.S. Light, 8 ex.; Gatineau, 45.464, −75.761, infesting L. latifolius seeds; Gatineau QC, eggs on pod 25.VI.2021, eggs hatch 6.VII, beetles hatch 18.VIII.2021, M.H.S. Light, 8 ex.; Gatineau, 45.464, −75.761, Dead Bruchus affinis from two seeds in a sealed commercial package of 25 L. latifolius seeds, 18.21.III.2021, M.H.S. Light, 2 ex.; Farm Point, 45.6092, −75.8975, 23.VI.2021, ex. roadside Lathyrus flowers, H. Douglas, 6 ex.; Laval, Boisé Papineau (Près St. Martin) sur marguerite, 45.60229, −73.68096, 19.VI.2013, S. Dumont, 1 ex.; Laval, Boisé Papineau, 45.60704, −73.68082, battage spirée en fleurs, 21.V.2014, S. Dumont, 1 ex.; Laval, Boisé Papineau, 45.603, −73.681, sur Lathyrus, 29.VII.2014, S. Dumont, 3 ex.; Laval, Contrecoeur, Camp des Grèves 45.979, −73.182, sur Lathyrus, 7.VIII.2009, S. Dumont, 3 ex.; Laval, Berge Olivier-Charbonneau 45.698, −73.529, sur L. latifolius, 21.VII.2021, S. Dumont, 22 ex.; Montréal, Anjou, près Parc Roger Rousseau 45.617, −73.545, sur L. latifolius, 22.VII.2021, S. Dumont, 20 ex.; Notre-Dame-de-l’île-Perrot (Vaudreuil), 4.VII.2007, Battage Lathyrus sp., Pierre de Tonnancour, 2 ex.; Notre-Dame-de-l’île-Perrot (Vaudreuil), 20.V.2011, Battage Caragana sp., Pierre de Tonnancour, 1 ex.; Notre-Dame-de-l’île-Perrot (Vaudreuil), 14.VI.2011, Battage Cirsium arvense, Pierre de Tonnancour, 1 ex.; Notre-Dame-de-l’île-Perrot (Vaudreuil), 20.V.2011, Battage Rubus odoratus, Pierre de Tonnancour, 1 ex.; Notre-Dame-de-l’île-Perrot (Vaudreuil), 31.VIII.2011, Battage Lathyrus latifolius, Pierre de Tonnancour, 1 ex.; Notre-Dame-de-l’île-Perrot (45.3775, −73.9431), 7.VI.2019, fauchage, champ humide, Pierre de Tonnancour, 1 ex. Ontario: Ottawa, Hurdman Bridge, 45.418, −75.664, 3.VII.2021, ex. Lathyrus flowers, 8 ex., H. Douglas (field photographs: https://www.inaturalist.org/observations/85903171. An additional female Bruchus specimen from near Québec City, seen only in internet photographs also has pronotal morphology matching B. affinis (https://www.inaturalist.org/observations/38795458), suggesting that B. affinis may also be established in that region.

We present evidence of 79 specimens from multiple sites in three provinces, separated by over 3500 km over 14 years, and rearing evidence of successful reproduction in nature. Together, these lead us to conclude that multiple populations of B. affinis are established in Canada.

Bruchus affinis can be distinguished from other North American Bruchus by the following combination of characters (adapted from key by Kingsolver 2004 using Borowiec 1988): antennae with three or four basal antennomeres red-brown; pronotum with lateral spines situated before pronotal midlength in anterodorsal view (Fig. 1D); male mid tibiae with two spines on ventral surface near apex (Fig. 2A); hind legs with femoral spine (Fig. 2B) extending apicad (not protruding ventrad beyond basal part of ventral surface, like Kingsolver 2004 fig. 257), mucro twice longer than lateral denticle (Fig. 2B); protibiae with some red-brown colouration on basal half, mesotibiae black (Fig. 1B). The broadly obtuse apex of the aedeagus is also unique among North American species (Fig. 2D). For rapid assessments, no other species has lateral spines situated on the anterior half of the pronotum and all black mesotibiae.

It was initially unknown whether the infestation of the index plant could represent the first establishment of a new population of B. affinis in Canada. Alternatively, we thought this infestation could have spread from a pre-existing adventive population. Later we found nearby patches of B. affinis-infested L. sylvestris. Finding these specimens as well as others from elsewhere in Canada (many collected before 2020) is consistent with spread of a pre-established adventive population rather than establishment of a new adventive population in the garden of the index plant resulting from planting infested seeds there.

Our finding of B. affinis specimens within seeds of L. latifolius that were commercially imported from Europe suggests that import of infested seed is a likely pathway for the introduction of this species to Canada. The discovery of B. affinis in Québec, Ontario, and British Columbia over only 15 years is consistent with multiple introductions over several years since our earliest specimen collection date in 2007. This is also consistent with movement of infested seed rather than haphazard introduction of adults (e.g. live beetles accidentally trapped in shipping containers). This evidence indicates that B. affinis was present in Canada for 15 or more years.

Bruchus affinis is known to infest seed pods of L. grandiflorus, Sibth. & Smith, L. latifolius, L. sylvestris, and L. tuberosus L. (Kergoat et al. 2007), all introduced species to North America, and Vicia sp. (Fabres et al. 1986). Knowledge that B. affinis harms only seeds indicates that it will not harm the ability of these plants to grow or perform ornamental and erosion control functions. The moderate observed impact of Bruchus predation on their seeds may somewhat reduce these plants’ ability to propagate. USA and Canada are also home to 29 named native Lathyrus species (USDA, 2022) plus other native Fabaceae. It remains unknown whether B. affinis can harm the reproductive outputs of these native species.

Bruchus affinis is also known to use Vicia faba as host in Europe (Segers et al. 2021), where it appears to act as a minor pest. In Europe, several species of Bruchus infest fava beans in the field. Of these, B. rufimanus is the most destructive (Segers et al. 2021). Bruchus rufimanus is listed as present in Canadian provinces producing fava beans (Bousquet et al. 2013); however, we were unable to find evidence that it causes economic damage to Canadian fava bean crops (e.g. Agrinova 2017). Together, these two findings may suggest that B. affinis is unlikely to cause substantial harm to fava beans in Canada.

This new North American record, added to the species counts by Douglas et al. (2021), indicate that Canada and the USA are together known to host 69–79 species of adventive Chrysomelidae, including 16–18 Bruchinae. Of these, 52–60 adventive Chrysomelidae are known from Canada, and 56–66 are known from the USA.

Flowering of both Lathyrus species began the week of June 15, 2021. The first L. latifolius pods developed by June 23 with the first eggs appearing on pods June 25: hatching began July 6. Mature, undehisced pods were collected from August 2 to August 12. Twenty-one B. affinis emerged from the 76 seeds (22 pods) on August 18–26 only: there were no further emergences. Seed infestation rate was 27.6%, averaging about one B. affinis larva per pod. Of the 21 tagged pods, 20 contained eggs (range 1–8 eggs per pod; median 3 eggs per pod). Overall, beetle reproduction on L. latifolius commenced as soon as flowers developed. Development of the new beetle generation was complete by the end of August, with about one quarter of seeds killed by beetles.

On L. sylvestris, 30 B. affinis adults were observed on June 27 on plants at five of eight roadside patches. Few B. affinis were seen after decrease in flower production in mid-July. The first 43 B. affinis individuals reared indoors emerged on August 14. Emergence of B. affinis collected from all eight patches on July 28 (104 pods/606 seeds) occurred mainly during two peak periods with warm weather: August 14–21 (preceded by five days of hot weather, 30–31 °C; indoor 27 °C), 68 beetles; and August 25–26 (daily max. 32.8–32.7 °C; indoor 27 °C; 92 beetles). Of all 215 beetles eclosed in August 2021, 160 were from these two periods. The infestation rate of the 606 seeds was 35% (13.5–73.5% across patches). If a pod had not yet dehisced, emerging beetles chewed exit holes to exit through the pod wall. The sound of chewing was audible outdoors from up to 2 m away. All observed beetles initiated flight immediately after exiting pods outdoors or within rearing containers. Flying behaviour in containers continued for several hours, after which emerging beetles no longer attempted flight. Dehisced or manually opened pods of both species revealed white tissue developing from the inner pod wall beneath egg positions (Fig. 3D). Beetle activity periods and seed infestation rates on L. sylvestris were similar to those on garden grown L. latifolius.

The earliest evidence of parasitism was September 1 when two different hymenopteran larvae were found within B. affinis-infested seeds. Hymenoptera parasitoids of B. affinis first emerged from mature seeds of L. sylvestris (collected September 5, 10, and 11. These were identified as Dinarmus basalis (Rodani, 1877), a cosmopolitan parasitoid of Bruchinae in legume seeds (Schmale et al. 2003) by John Huber and Gary Gibson (CNCI). Bruchus affinis and parasitoid emergence holes from seeds were distinguishable, allowing ML to score beetle and parasitoid infestation rates. Holes made by reared B. affinis were circular, 1.5–2.1 ± 0.02 mm in diameter (n = 63, median: 1.9 mm), while those from parasitoids were smaller and circular: 0.6–1.2 ± 0.02 mm (n = 27, 0.8 mm). The 438 seeds collected for rearing from patch 5 on September 5 resulted in 19 parasitoid emergence holes plus one pre-emergent parasitoid or 8% parasitism of developing B. affinis. Bruchus affinis was confirmed as host of the parasitoid by examination of the host remains by ML. In most cases, the remains of the beetle, including elytra and mandibles, could be used to confirm that a pupa (Fig. 4) was host to the parasitoid. Fig. 5A shows a parasitoid larva was feeding on a teneral beetle when a field-collected seed was opened on October 26. Here, the parasitoid may have continued feeding later into the autumn because of warmer indoor rearing conditions.

Figure 4. 

Bruchus affinis pupal stages in seeds of L. sylvestris from Québec, Canada. Scale bars: 2 mm.

Figure 5. 

A Bruchus affinis, parasitized by Hymenoptera larvae in seed of L. sylvestris B maturing pods of L. sylvestris with hatched and unhatched eggs C dehisced pod of L. latifolius D dehisced pod of L. sylvestris showing B. affinis exit holes in pod wall and seed. Scale bars: 2 mm (A); 25 mm (B); 50 mm (C); 20 mm (D).

Onset of host flowering was about two weeks earlier in Québec (mid-June) than reported from France (early July) (Bashar et al. 1987). Fabres et al. (1986) reported that adult B. affinis in France lived about 11 months after emergence including a nine-month reproductive diapause reporting that first pods appropriate to oviposition were present in mid-July with a maximum number of available pods for oviposition present in mid-August. We found that eggs were laid at our study site slightly earlier (about June 25). The period of sexual reproduction of B. affinis was short. We observed few B. affinis on Lathyrus plants after mid-July.

In summary, we report the following from North America (Québec): infestation of L. latifolius and L. sylvestris (Fabaceae) by Bruchus affinis; rearing of B. affinis from both hosts; oviposition in 2021 beginning late June, to adult emergence beginning mid August; observation of B. affinis adults chewing holes to exit undehisced pods of L. sylvestris; parasitization of B. affinis by Dinarmus basalis in Québec. We also found that the seed emergence hole diameter of B. affinis was consistently larger than that of parasitoid emergence holes, such that we could reliably distinguish between exit hole types. We quantified B. affinis seed infestation rates of L. latifolius (17–28%), and of L. sylvestris (13.5–73.5%) for 2021.