title: Seasonal adaptations to day length in ecotypes of Diorhabda spp. (Coleoptera: Chrysomelidae) inform selection of agents against saltcedars (Tamarix spp.).
abstract: Seasonal adaptations to daylength often limit the effective range of insects used in biological control of weeds. The leaf beetle Diorhabda carinulata (Desbrochers) was introduced into North America from Fukang, China (latitude 44° N) to control saltcedars (Tamarix spp.), but failed  to establish south of 38° N latitude because of a mismatched critical daylength response for diapause induction. The daylength response caused beetles to enter diapause too early in the season to survive the duration of winter at southern latitudes. Using climate chambers, we characterized  the critical daylength response for diapause induction (CDL) in three ecotypes of Diorhabda beetles originating from 36, 38, and 43° N latitudes in Eurasia. In a field experiment, the timing of reproductive diapause and voltinism were compared among ecotypes by rearing the insects on plants  in the field. CDL declined with latitude of origin among Diorhabda ecotypes. Moreover, CDL in southern (<39° N latitude) ecotypes was shortened by more than an hour when the insects were reared under a fluctuating 35-15°C thermoperiod than at a constant 25°C. In the northern  (>42° N latitude) ecotypes, however, CDL was relatively insensitive to temperature. The southern ecotypes produced up to four generations when reared on plants in the field at sites south of 38° N, whereas northern ecotypes produced only one or two generations. The study reveals  latitudinal variation in how Diorhabda ecotypes respond to daylength for diapause induction and how these responses affect insect voltinism across the introduced range.
authors.affiliation: Marine Science Institute, University of California at Santa Barbara, CA 93106-6150, USA. Peter.Dalin@ekol.slu.se
authors.forename: Peter
authors.initials: P
authors.lastname: Dalin
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Bean
authors.forename: Tom L
authors.initials: TL
authors.lastname: Dudley
authors.forename: Vanessa A
authors.initials: VA
authors.lastname: Carney
authors.forename: Debra
authors.initials: D
authors.lastname: Eberts
authors.forename: Kevin T
authors.initials: KT
authors.lastname: Gardner
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Hebertson
authors.forename: Erin N
authors.initials: EN
authors.lastname: Jones
authors.forename: David J
authors.initials: DJ
authors.lastname: Kazmer
authors.forename: G J
authors.initials: GJ
authors.lastname: Michels
authors.forename: Scott A
authors.initials: SA
authors.lastname: O'Meara
authors.forename: David C
authors.initials: DC
authors.lastname: Thompson
mesh_terms: D000818:Animals; D061046:Biological Control Agents; D001517:Coleoptera / Q000254:growth & development / Q000502:physiology*; D060146:Ecotype; D005260:Female; D007814:Larva / Q000254:growth & development / Q000502:physiology; D017440:Photoperiod; D011679:Pupa / Q000254:growth & development / Q000502:physiology; D012098:Reproduction; D012621:Seasons; D032363:Tamaricaceae; D013696:Temperature; D014481:United States
chemical_list: D061046:Biological Control Agents