Mixed significance of plant vigor: two species of galling Pontania in a hybridizing willow complex

• Published in: Oikos
• Main Author: Kokkonen, Katri
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2000
• Subjects: Subarctic
• Online Access: http://dx.doi.org/10.1034/j.1600-0706.2000.900110.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1034%2Fj.1600-0706.2000.900110.x; https://onlinelibrary.wiley.com/doi/pdf/10.1034/j.1600-0706.2000.900110.x

Distributions of leaf galls and offspring performance of two Pontania sawfly species were explored in individual willows of the subarctic Salix caprea – starkeana hybrid complex. The more common sawfly, an undescribed species near the dolichura group (P1), had the highest gall numbers in trees with long shoots both in S. caprea and hybrids. While numbers were high on vigorously growing hybrids, offspring of P1 were aborted significantly more often on hybrids than on pure hosts. Further, non‐aborted galls were smaller on hybrids. Fast shoot growth may be important for P1 sawflies, because females oviposit early in summer and larvae develop rapidly compared with the other species, Pontania pedunculi (P2). Distributions of P2 galls were related to tree height and not to shoot length in both parental and hybrid groups of willows. Like P1, also P2 offspring were frequently aborted on hybrids, but not significantly more often than on pure hosts, and P2 galls were equally large among the host groups. Survival of both species was related to abortion rates, while larvae were parasitized equally in all host groups. This study demonstrates that the significance of plant vigor may vary even for closely related galling sawflies exploiting the same hosts, or for the same species on different host plants. Vigorous growth may mislead gallers to oviposit on suboptimal plants.