Field and laboratory studies investigated the preimaginal developmental time, adult emergence phenology, mating behavior, and weevil hosts of Necremnus tidius (Walker) (Hymenoptera: Eulophidae), a solitary ectoparasitoid of coleopteran larvae. In addition, changes in parasitism levels of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), by N. tidius were determined during 2003–2005 in commercial fields of canola (Brassica rapa L. and Brassica napus L.) in southern Alberta and Saskatchewan, Canada. Mean ± SE developmental time from egg to adult was 18.3 ± 0.23 d for specimens reared at 21°C and a photoperiod of 12:12 (L:D) h. Emergence began in late July in commercial fields near Lethbridge, AB, and 20 d later 81% of the population had emerged. Emergence was completed by the end of August. Mating was preceded by a complex courtship behavior with the male standing on the dorsum of the mesosoma and gaster of the female, flapping its wings without flight, leaning forward and stroking its antennae over the antennae of the female, leaning back, and repeating the sequence several times. The native weevil Ceutorhynchus neglectus Blatchley was determined to be an alternate host of N. tidius in central and northern Alberta. N. tidius was found in few commercial canola fields in 2003, but in 2004, it occurred over hundreds of thousands of hectares of canola cropland, reaching peak parasitism levels of 45%. In 2005, N. tidius was still common, but parasitism declined relative to that observed in 2004.
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Vol. 100 • No. 6