New Zealand distribution and seasonal incidence of the nematode,Sphaerularia bombiDufour, a parasite of bumble bees

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Abstract
In New Zealand the nematode Sphaerularia bombi Dufour is currently confined to an area of about 30–40 km around Christchurch, where bumble bees were originally released. The spread of this nematode has been much slower than that of its bumble bee hosts during the 100 years since their introduction. Levels of apparent parasitism of up to 56% in B. terrestris (L.) and 7% in B. hortorum (L.) were detected. The incidence of S. bombi queens foraging in spring rises sharply as healthy queens become unavailable when they start their nests. Estimated mortality levels caused by S. bombi are between 3–10% in both B. terrestris and B. hortorum. These levels are lower than in Europe. Infected B. terrestris averaged 5.0 nematode uteri per host and B. hortorum 1.7 uteri per host, which is similar to records from Europe. The status of S. bombi as a parasite of Vespula queens remains uncertain.