Tolerance response of E. annuus against the attack of
girdling beetle P. rufiventris
We characterized the life history of E. annuus with and without
the attack of P. rufiventris (Fig. 1). Overwintered E.
annuus began to bolt in April and produced flowers in May. The seeds
germinated and overwintered at the rosette stage. P. rufiventrislaid an egg inside the stem of E. annuus after girdling the stem
from April to May. Girdling behavior killed the upper part, stimulating
axillary bud emergence. Seed production in girdled E. annuus was
therefore delayed compared with that in non-girdled E. annuusplants.
To assess the fitness loss caused by girdling beetles, we measured the
number of flowers in experimentally girdled and non-girdled E.
annuus plants with and without larval attack. Three weeks after
girdling and egg inoculation, girdled E. annuus produced
significantly fewer flowers than the non-girdled E. annuus (Fig.
2a). Flower production was not affected by larval feeding inside the
stems.
We then measured the long-term effects of girdling on E. annuusgrowth and reproduction of naturally girdled E. annuus in the
field. Two weeks after girdling, girdled E. annuus plants had
higher chlorophyll content than non-girdled plants (Fig. 2b).
Subsequently, the axillary bud emergence was boosted in girdled E.
annuus, and the number of branches exceeded that in non-girdledE. annuus 4 weeks after girdling (Fig. 2c). The extra branches of
girdled E. annuus persisted throughout the flowering season ofE. annuus . The higher number of axillary branches in girdledE. annuus led to flower production restoration. Initially,
girdled E. annuus plants produced significantly fewer flowers
than non-girdled plants. However, the difference diminished over time
and lost significance seven weeks after girdling (Fig. 2d).
Consequently, the difference in the number of flowers in girdled and
non-girdled E. annuus was not significant by 12 weeks after
girdling when the flowering season of E. annuus was complete.
Because seed number per flower is proportional to flower size inE. annuus , we further compared flower sizes. The flower size of
girdled and non-girdled E. annuus did not differ significantly
(Fig. 2e). Thus, we concluded that the loss of shoot apical meristems in
girdled E. annuus restores reproductive production by boosting
growth at the end of the life cycle.