Could hybridization increase establishment success of the biological
control agent Aphalara itadori (Hemiptera: Aphalaridae) against invasive
knotweeds?
Abstract
Intraspecific hybridization between distinct populations could increase
fitness and adaptive potential of biological control agents that often
have low genetic diversity and can be inbred due to long-term laboratory
rearing often at small population sizes. Hybridization can also alter
host preference and performance when the parental insect populations are
adapted to different host plants. We investigated the effects of
hybridization between two populations (Northern and Southern) of the
psyllid, Aphalara itadori, that have different fitness on three invasive
knotweed species (Japanese, giant, and Bohemian). Fecundity, host
choice, and developmental success of second-generation reciprocal
hybrids and the parental psyllid populations were compared on the three
knotweed species in multiple choice tests. Hybridization did not
increase fecundity. All three knotweed species were accepted for
oviposition without preference by the Southern and the two hybrid
psyllid populations. The northern psyllid population laid the most eggs
on Bohemian knotweeds but those were maladaptive choices since almost
all eggs failed to develop. Developmental success of the parental
psyllid populations was highest on the knotweed species they were
originally collected from, on Japanese knotweed of the Southern psyllids
and on giant knotweed of the Northern psyllids. Hybrids had intermediate
or higher survival on given knotweed hosts compared to their parents.
These results can inform release tactics of A. itadori in different
regions especially where there appears to be climatic and/or host
mismatches such as in Michigan. In southern Michigan, based on climate
the Northern psyllid population should be released. However, the most
common knotweed species in the region are Bohemian and Japanese
knotweeds that do not support development of the Northern psyllids. In
this case, hybrids that may carry cold adaptations of the Northern
psyllids but have better developmental success on the prevailing
knotweed species may be considered for release to increase establishment
success.