Cues from a specialist herbivore increase tolerance to defoliation in tomato

1. Recent studies have shown that herbivore cues trigger rapid shifts in primary metabolism and resource allocation within a plant. This has been suggested to be an induced mechanism of tolerance to defoliation but there is little evidence supporting this. Here, we investigated, using a cultivar of tomato (Solanum lycopersicum), whether prior herbivore damage confers plants an advantage in terms of increased growth and initial flower production following defoliation. 2. Plants were mechanically wounded and treated with either regurgitant of the specialist Manduca sexta, deionized water or received no damage for five consecutive days. Chlorophyll content, plant growth and biomass allocation were measured during the 5-day damage period. After the damage treatments, all leaves were removed to simulate defoliation in the three treatment groups, and regrowth capacity was followed until flowering. The number of regrown leaves, the initial number of flowers and biomass production and allocation were quantified at harvest. 3. During the 5-day damage period, plants treated with M. sexta regurgitant grew less in height than undamaged plants (but had thicker stems). Chlorophyll content also decreased sharply in these plants. However, regurgitant-treated plants recovered more quickly from the defoliation treatment, producing more new leaves compared with undamaged and mechanically damaged treatments. 4. Our results support the hypothesis that induced changes in resource allocation in response to specialist herbivores results in increased regrowth ability and may be adaptive in the event of severe defoliation. Future studies on wild plants could help inform the evolutionary significance of this response.