Results
There was no difference in the fecundity of the parental and hybridA. itadori populations (F3, 20 = 1.03, P =
0.3988). The 25 females released within each cage (replicate) of the
Kyushu parent laid 292 ± 57 (mean ± SE), the Hokkaido parent 447 ± 70,
the FemKYU hybrid 396 ± 66, and the FemHOK hybrid 378 ± 65 eggs on
average across the three knotweed species offered. The different psyllid
populations tended to lay similar number of eggs (F3,20= 1.02, p = 0.4052) on the three knotweed species (F2,40= 2.56, p = 0.0902) except for the Hokkaido population (psyllid
population*plant species: F6,40 = 2.79, p = 0.0233)
(Fig. 1). Hokkaido females laid significantly more eggs on Bohemian
knotweeds (206.4 ± 38.7) than on Japanese knotweeds (74.9 ± 23.3) while
the Kyushu parent and the hybrids did not discriminate among knotweed
species.
There were significant differences in development success of nymphs from
the four psyllid populations on the three knotweed species (psyllid
population*plant species interaction: χ = 833.87, df = 6, p <
0.001) (Fig. 2). The FemHOK hybrid was the only psyllid population that
had similar developmental success on all three knotweed species. The
Hokkaido and Kyushu parent had the highest survival on their optimal
hosts of giant and Japanese knotweeds respectively, while the FemKYU
hybrid performed best on Bohemian knotweed.
In the cross where the female is from the Hokkaido population and the
male is from Kyushu (FemHOK) hybridization significantly increased
survival on Bohemian (36%) and Japanese knotweeds (45%) compared to
the Hokkaido parent (< 7%). However, hybridization also led
to lower development success on giant knotweeds (37%) compared to the
maternal parent (63%). For the other type of cross where the female was
from Kyushu (FemKYU) there was some decline in survival on Bohemian
knotweeds (52%) compared to the maternal parent (63%) and a larger
reduction on Japanese knotweed (21%) compared to the Kyushu parent
(61%). On giant knotweed both reciprocal crosses had similar
performance as the Kyushu parent (Fig. 2).