Is the response of insect herbivores to elevated CO 2 and temperature universally predictable for different host tree species? Andrew Gherlenda Dr. Tony Haigh, Dr. Ben Moore, Dr. Scott Johnson, Dr. Markus Riegler

Impacts on insect herbivores Altered leaf chemistry at elevated CO 2 and temperature Species-specific responses to climate change Eucalypt foliage relatively nutrient poor Reduced foliar quality may; – Decrease survival, pupal weight – Increase developmental time Ainsworth & Rogers, 2007, GCB, Stiling & Cornelissen, 2007, GCB, Robinson et al., 2012, New Phytol

Immune response Encapsulation and melanisation via phenoloxidase (PO) cascade main defence against parasitoids and entomopathogens Activating an immune response is energetically expensive Smilanich et al., 2009, Ecology, Freitak et al., 2003, P Roy Soc Lond B Bio

Objectives Determine the effects of elevated CO 2, temperature and their interactions on herbivore performance Assess if insect response to eCO 2 and eT are consistent between different host plant species Assess whether the immune response of larvae was altered as a result of elevated CO 2 and temperature

Insect and host species Eucalyptus tereticornis Eucalyptus robusta Atlas of living Australia 2013 Paropsis atomaria (Coleoptera: Chrysomelidae) CAB International, 2005

Method Four CO 2 x temperature combinations – CO 2, 400 vs. 640 ppm – Temperature, 26:18 °C vs. 30:22 °C (15:9 hours) Larvae were placed onto trees (n=10) in a split brood design Expanding leaves analysed for foliar chemistry

Leaf quality decreases at eCO 2 E. robustaE. tereticornis CO 2 TemperatureInteractionCO 2 TemperatureInteraction Nitrogen n.s Phosphorous n.s C:N n.s TNC n.s

Survival increases at eCO 2 on E. robusta P = P = CO 2 P = CO 2 P = 0.023

Longer developmental time at eCO 2 P = CO 2 P <0.001 Temp P <0.001 CO 2 P <0.001 Temp P = 0.003

Decreased pupal weight at eCO 2 CO 2 P <0.001 CO 2 P = 0.003

Reduced insect performance Response fairly predictable across different hosts – Survival may improve on some host species at eCO 2 eCO 2 is main factor in reduced insect performance mediated by leaf chemistry – Temperature had limited effect – Compensatory feeding did not overcome reduced leaf quality

Immune response (defence) Eucalyptus tereticornis only Implanted with a nylon filament (2 mm long 0.25 mm diameter) Assay of: – Phenoloxidase (PO) activity – Haemolymph protein content – Encapsulation response (darkening of nylon filament)

Reduced E. tereticornis foliar traits CO 2 P <0.001 CO 2 P = Temp P = 0.002

Immune traits PO activity Haemolymph protein Encapsulation response CO 2 Temperaturen.s

Immune traits P = 0.018P = P = 0.030

Reduced defence at eCO 2 Insect herbivores may be more susceptible to attack at eCO 2 as a result of decreased PO activity – Encapsulation response may mediate this PO activity indirectly affected by foliar chemistry

Responses predictable? Elevated CO 2 reduces the growth and defence of larval insect herbivores mediated by reductions in plant nutrition – Reduced abundance in future?? In general, the response of herbivores to climate change is similar on different hosts – Localised benefits may occur Hamilton et al., 2012, Acta Oecol, Stiling et al., 1999, Ecol Appl

Acknowledgments Goran Lopaticki Aidan Hall James Ryalls Riegler’s lab group Hawkesbury Institute for the Environment CSIRO tree seed centre