A Survey of Aphid Species and their Associated Natural Enemies in Fraser Valley Hop Fields and an Exploration of Potential Alternative Summer Hosts of the Damson-Hop Aphid, Phorodon humuli (Hemiptera: Aphididae)
Six hop fields, Humulus lupulus (Rosales: Cannabaceae), in the Fraser Valley, British Columbia, were surveyed throughout 2019 to determine the composition of aphid species and their associated natural enemies. The host range of a known aphid pest of hops, the damson-hop aphid, Phorodon humuli (Hemiptera: Aphididae), was also explored in order to further clarify its summer host range and lifecycle. Phorodon humuli collected from Prunus spp. were reared and transferred to potential alternative hosts including Cannabis sativa (Rosales: Cannabaceae) and nettle, Ultica dioic (Rosales: Urticaceae). Phorodon humuli was the dominant aphid species found in all six hop fields in 2019, comprising 99% of all aphids found. Phorodon humuli were found in hop fields from May 24, 2019 through to November 3, 2019. Other aphid species were present in some hopyards early in the season including Aphis fabae (black bean aphid), Macrosiphum euphorbiae (potato aphid) and Brachycaudus helichrysi (leaf-curling plum aphid). Phorodon cannabis (hemp/cannabis/bhang aphid) was not found in any of the six hop fields. Ladybird beetles (Coleoptera: Coccinellidae) were the most abundant predator found on hop leaves, making up 76% of all aphidophagous predators found in the six hop fields. Orius spp. were the most abundant predator found in hop burrs and cones, contributing to 97% of all aphidophagous predators found in the six hop fields. Predator population growth was low compared to aphid population growth. In host-transfer experiments, P. humuli decreased on cannabis and nettle, while increased on hops, indicating that cannabis and nettle are not a preferred summer hosts of P. humuli.