Seasonal adaptations to day length in ecotypes of Diorhabda spp. (Coleoptera: Chrysomelidae) inform selection of agents against saltcedars (Tamarix spp.)

Authors: DALIN, PETER - University Of California; BEAN, DANIEL - Colorado Department Of Agriculture; DUDLEY, TOM - University Of California; CARNEY, VANESSA - Texas A&M University; EBERTS, DEBRA - Bureau Of Reclamation; GARDNER, KEVIN - New Mexico State University; JONES, ERIN - Texas A&M University; Kazmer, David; MICHELS JR, G - Texas A&M University; O'MEARA, SCOTT - Us Bureau Of Reclamation

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2010
Publication Date: 10/1/2010
Citation: Dalin, P., Bean, D.W., Dudley, T., Carney, V.A., Eberts, D., Gardner, K.T., Jones, E.M., Kazmer, D.J., Michels Jr, G.J., O'Meara, S.A. 2010. Seasonal adaptations to day length in ecotypes of Diorhabda spp. (Coleoptera: Chrysomelidae) inform selection of agents against saltcedars (Tamarix spp.). Ecological Entomology. 39(5): 1666-1675.

Interpretive Summary: 1. Seasonal adaptations to day length often limit the effective range of biocontrol insects. The leaf beetle Diorhabda carinulata was introduced into North America from Fukang, China (latitude 44°N) for the biocontrol of saltcedars (Tamarix spp.), but failed to establish below 38° latitude because of a mismatched critical day length response for diapause induction which caused beetles to enter diapause too early in the season to survive the winter at southern latitudes. 2. Using climate chambers, we characterized the critical day length response for diapause induction (CDL) in three ecotypes of Diorhabda beetles originating from 36°, 38° and 43° latitudes in Eurasia. In a field experiment, the timing of reproductive diapause and voltinism was compared among ecotypes by rearing the insects on plants in the field. 3. CDL declined with latitude of origin among Diorhabda ecotypes. Moreover, CDL in southern (<40° latitude) ecotypes was shortened by more than an hour when the insects were reared under a fluctuating 35-15°C thermoperiod than at constant 25°C. In the northern (>40° latitude) ecotypes, however, CDL was relatively insensitive to temperature. 4. The southern ecotypes produced up to four generations when reared on plants in the field at sites below 38°, whereas northern ecotypes produced only one or two generations. 5. The study reveals latitudinal variation in how Diorhabda ecotypes respond to day length for diapause induction and how these responses affect insect voltinism across the introduced range.

Technical Abstract: 1. Seasonal adaptations to day length often limit the effective range of biocontrol insects. The leaf beetle Diorhabda carinulata was introduced into North America from Fukang, China (latitude 44°N) for the biocontrol of saltcedars (Tamarix spp.), but failed to establish below 38° latitude because of a mismatched critical day length response for diapause induction which caused beetles to enter diapause too early in the season to survive the winter at southern latitudes. 2. Using climate chambers, we characterized the critical day length response for diapause induction (CDL) in three ecotypes of Diorhabda beetles originating from 36°, 38° and 43° latitudes in Eurasia. In a field experiment, the timing of reproductive diapause and voltinism was compared among ecotypes by rearing the insects on plants in the field. 3. CDL declined with latitude of origin among Diorhabda ecotypes. Moreover, CDL in southern (<40° latitude) ecotypes was shortened by more than an hour when the insects were reared under a fluctuating 35-15°C thermoperiod than at constant 25°C. In the northern (>40° latitude) ecotypes, however, CDL was relatively insensitive to temperature. 4. The southern ecotypes produced up to four generations when reared on plants in the field at sites below 38°, whereas northern ecotypes produced only one or two generations. 5. The study reveals latitudinal variation in how Diorhabda ecotypes respond to day length for diapause induction and how these responses affect insect voltinism across the introduced range.