Trupanea vicina (Wulp) (Diptera: Tephritidae), a new pest of marigold production on California’s central coast: Field life history, colony development and pesticide efficacy trials

Trupanea vicina (Wulp), a California native tephritid fruit fly, has recently become a seed-feeding pest of commercial marigold production in Santa Barbara County. This rare, nonfrugivorous species was known only from a few species of Asteraceae in the subtribe Pectidinae in southern California desert regions. In commercial settings on the central coast, seed production was reduced 50% in the last two years. Studies were initiated in 2009 to test the efficacy of low-risk pesticides and determine feeding damage, life history and host plant associations. A continuously breeding colony was established for T. vicina, a first for this fly genus. Pesticide trials with dinotefuran, imidacloprid, cyfluthrin, spinosad, and spirotetramal showed populations were significantly reduced in laboratory settings. Pesticides with systemic activity had the highest efficacy. Field samples taken in fall 2009 had up to 61% of flower heads with eggs in them. There were as many as 36 eggs in a single flower head. At least 1 larva was present in 78% of the flower heads and up to 11 larvae in a single flower head. The highest observed feeding damage was 44 seeds per flower head with flowers averaging 47.7 ± 13.9 (n=113; range=76/14) seeds per head. A single generation took approximately 4 weeks under laboratory conditions. Adults were reared from feral plants collected in early December; additionally, over 1,600 adults were reared from volunteer plants collected from fallow fields in mid-April. Four species of Asteraceae were collected from weedy and natural areas surrounding marigold production fields and placed into rearing cages; no T.vicina were reared from these samples.