Biology Reference
In-Depth Information
321
Cionus hortulanus
(Fourcroy) (
321
)
Mullein weevil
This locally common weevil also infests cultivated
mullein (
Verbascum
) but has a more restricted host
range than the previous species, being found most often
on dark mullein (
V. nigrum
). Adults of both species of
Cionus
are similar in appearance but
C. hortulanus
is
slightly smaller (3.5-4.0 mm long) and paler in colour,
the elytra appearing mainly yellowish grey or greenish
grey, interrupted by two black patches and a distinct
pattern of small black markings.
Cryptorhynchus lapathi
(Linnaeus) (
322-323
)
syn.
Cryptorhynchidius lapathi
(Linnaeus)
Osier weevil
A locally important pest of poplar (
Populus
), notably
hybrid black poplar (
P. serotina
), and willow (
Salix
);
also associated with alder (
Alnus
) and, less frequently,
birch (
Betula
). Often damaging in nursery beds,
including basket-willow beds. Widely distributed in
Europe, including the Czech Republic, England, France,
Germany, Hungary, Italy, the Netherlands, Poland,
Spain, Wales and Yugoslavia; introduced into North
America.
321
Mullein weevil (
Cionus hortulanus
).
322
DESCRIPTION
Adult:
8-9 mm long; robust; mainly black, interspersed
with white or yellowish-white scales, particularly
towards the base and at the apex of the elytra.
Egg:
1 mm long; creamy white.
Larva:
up to 10 mm
long; creamy white, with a brown head.
322
Osier weevil (
Cryptorhynchus lapathi
).
323
LIFE HISTORY
In subtropical areas and southern Europe, this insect has
a one-year lifecycle. In most parts of Europe, however,
development usually extends over two years. Adults
emerge in the spring, from May onwards. They usually
remain hidden beneath host plants during the day and
become active in the evening, crawling up the stems to
feed on the young shoots. They are very sluggish,
dropping to the ground if disturbed; although fully
winged, they rarely, if ever, fly. Adults continue to feed
throughout the summer and autumn, mated females
eventually laying eggs singly in the rods and stools of
host plants. Surface wounds, leaf scars and lenticels are
often chosen as oviposition sites, the females boring out
a cavity before depositing a single egg a few millimetres
beneath the surface. Eggs hatch in about three weeks.
Irrespective of when eggs are laid, the larvae feed only
briefly during the first season; they then enter diapause,
still in their first instar, to resume activity in the
following spring. The larvae feed within the host tissue
for several months, ejecting whitish frass through a hole
323
Osier weevil (
Cryptorhynchus lapathi
) damage to shoot
of
Populus
.
Search WWH ::
Custom Search