Herbivore induced plant volatile specificity and its affect on host plant selection by an herbivorous two-spotted spider mite

Background/Question/Methods

When plants are damaged by arthropod herbivores they release a suite of volatile organic compounds (VOCs), referred to as herbivore induced plant volatiles (HIPVS).  Numerous studies have found that predators and parasitoids are generally attracted to HIPVs both in the lab and field.  However, there is no general consensus about whether or not herbivores are or should be attracted to or repelled by HIPVs.  In a previous study, I found that herbivorous two-spotted spider mites (Tetranychus urticae) are attracted to HIPVs from conspecific feeding damage on cotton (Gossypium hirsutum).  After establishing this preference, I investigate to what extent herbivores are able to access and use specific information in plant volatiles related to host quality. Differences in HIPVs may allow herbivores to differentiate between good and bad host-plants by providing information about patch and host-plant quality. I tested spider mite preference for plant volatiles from all paired combinations of fertilized and unfertilized cotton plants with and without spider mite feeding damage in a y-tube olfactometer.  I also collected and analyzed cotton volatiles in order to correlate differences in preference to differences in volatile blends between treatments. 

Results/Conclusions

I found that spider mites prefer the volatiles from fertilized plants to unfertilized plants when both plants are undamaged.  Spider mites also preferred fertilized plants with spider mite damage over unfertilized plants without damage.  However when both fertilized and unfertilized plants received spider mite damage, spider mites exhibited no preference.  Surprisingly, spider mites preferred fertilized undamaged plants to unfertilized damaged plants.  These results indicate a trade-off between a known preference for conspecific damage and plant quality.  Spider mites prefer higher quality plants even when presented with conspecific damage, which may be attractive for a number of different reasons.  Differences in volatile blends between treatments show how fertilization affects HIPV blends and how spider mites are able to assess information about plant nutritional quality in order to make decisions prior to sampling.