Seasonal synchrony of life cycles between the exotic predator, Pseudoscymnus tsugae (Coleoptera: Coccinellidae) and its prey, the hemlock woolly adelgid Adelges tsugae (Homoptera:Adelgidae)

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1 The seasonal synchrony between the exotic predator, Pseudoscymnus tsugae and its prey, the hemlock woolly adelgid, Adelges tsugae, was investigated in field cages and in the forest in Connecticut, U.S.A. from 1997–1999.

2 In early spring, egg to adult development took 45 d at 18.7 °C, 39.7 d at 20.2 °C and 31.5 d at 22.7 °C. Earliest emerging F1 adults mated and oviposited in the same year. whereas F1 and F2 females emerging later in the summer mated and reserved most of their egg complement for the following year.

3 A second generation of P. tsugae is possible in Connecticut but may be delayed by cool mid-spring temperatures. Individuals of three generations of P. tsugae, including overwintering survivors, may coexist in July and August and adults can be found year-round with A. tsugae in infested hemlock forests.

4 A linear regression model for development from egg to adult under field temperatures gave good agreement with results from constant temperature findings. The model predicted a lower development threshold of 9.5 °C and a sum of effective temperatures of 405 day °C. Development time of P. tsugae is shorter relative to its prey A. tsugae and generation time ratios of predator to prey was 0.16–0.5, with an advantage conferred on the coccinellid.

5 Overwintering ability and behaviour were determined in 1998–1999 and adults remained on infested hemlock branches throughout a mild winter, becoming reproductively active in mid-April. Peak oviposition period extended from April to July, in synchrony with peak oviposition and developing stages of two generations of A. tsugae.

Keywords: Adelges tsugae; Coccinellidae; Pseudoscymnus tsugae; Tsuga spp; field development; overwintering; oviposition; synchrony

Document Type: Research Article

Affiliations: Connecticut Agricultural Experiment Station, Valley Laboratory, PO Box 248, Windsor, CT 06095, U.S.A.

Publication date: November 1, 2000

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