IngentaConnect Seasonal Timing of Diapause Induction Limits the Effective Range ...

Authors: Bean, Daniel W.¹; Dudley, Tom L.; Keller, Julie C.

Source: Environmental Entomology, Volume 36, Number 1, February 2007 , pp. 15-25(11)

Publisher: Entomological Society of America

Abstract:

The leaf beetle Diorhabda elongata Brullé subspecies deserticola Chen, collected in northwestern China, has been released in the western United States to control tamarisk (Tamarix spp.). While beetle establishment and saltcedar defoliation have been noted at northern study sites, this species has not established at latitudes south of the 38th parallel. Critical daylength for diapause induction was measured in the laboratory and ranged between 14 h 50 min to 15 h 08 min, depending on temperature, and adults were shown to cease reproduction and enter diapause at daylengths of 14 h 30 min or less. Critical daylength in the field was measured at ≈14 h 39 min and occurred 13 d before 50% of the population reached diapause. South of 36°20′ N, the longest days of the year are shorter than 14 h 39 min, making the beetles univoltine in the southern United States. North of 36°20′ N, a window of reproductive activity opens 13 d after the critical daylength is reached in the spring and closes 13 d after it is passed in the summer, allowing at least a partial second summer generation. It is predicted that south of the 38th parallel, premature diapause will increase mortality and disrupt synchrony between the life cycle of the beetle and host plant availability. This could hinder establishment and help explain the failure of this population south of the 38th parallel, providing a rationale for testing other populations of D. elongata in the southern range of Tamarix in North America.

Keywords: Diorhabda elongata; photoperiod; thermoperiod; tamarisk; biocontrol

Document Type: Research article

Affiliations: 1: Department of Plant Sciences, One Shields Ave., University of California, Davis, CA 95616, USA; USDA-ARS, Exotic and Invasive Weeds Unit, 800 Buchanan St., Albany, CA 94710, USA

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Seasonal Timing of Diapause Induction Limits the Effective Range of Diorhabda elongata deserticola (Coleoptera: Chrysomelidae) as a Biological Control Agent for Tamarisk (Tamarix spp.)