|
Summary
This insect causes highly visible damage in the native range.
Females girdle stems, ring-barking them, and ovipositing eggs
upstream of the girdle. The immediate result of girdling is
pruning resulting in a reduction in the total photosynthetic
area of the tree (Ueckert et al. 1971) and a loss of stored
carbohydrates (stored in small stems). Outbreaks of O.
rhodosticta in the native range is localised but damage
levels can be very high. Preliminary work suggests a high
incidence of parasitic wasps may hold populations in check
(Ueckert et al. 1971).
This insect proved very difficult to culture in the laboratory
and unexplained adult mortalities prevented detailed testing
of adult feeding host specificity. However, very preliminary
data suggested it might not be sufficiently host-specific
to release in Australia.
Taxonomy and origin
The new-world genus, Oncideres, contains more than
70 species, mainly of tropical and subtropical distribution
(Dillon & Dillon 1945, in Rice 1986). Only four species
occur north of Mexico (Linsley & Chemask 1984, in Rice
1986). O. rhodisticta has been recorded from Mexico,
and south-western USA (Linsley 1940), namely Arizona and Texas
(including the following vegetation zones: Edwards Plateau,
High Plains, Rolling Plains, and Trans-Pecos) (Ward et al.
1977, and refs therein).
Three Oncideres species (O. cingulata, O.
germari, and O. pustulata) have been recorded from
Prosopis glandulosa, and have been commonly confused
in the literature (Ward et al. 1977).
Adult O. rhodosticta are 1.5-2cm long, charcoal black
in colour, with a transverse grey band across the elytra.
Each elytron is dotted with about 35-40 small patches of orange
pubescence.
Lifecycle
In the native range adults emerge from galleries in girdled
branches of P. glandulosa from late August/early September
(depending on locality) to late November (Polk and Ueckert
1973). They feed upon tender bark around the buds, thorns
and small limbs (Polk and Ueckert 1973) for several days prior
to mating and subsequent girdling. In field cages most adults
died in 20-30 days, although a few lived more than 45 days
(Polk and Ueckert). Adults mate and lay eggs before killing
frosts occur (Ueckert et al. 1971)
Both sexes behave similarly when disturbed, dropping from
the mesquite tree to the ground, where they remain motionless.
When captured, they stridulate by rubbing the pronotum over
the ridged mesonotal plate (Polk and Ueckert 1973). Diurnal
and nocturnal mating occurs, even whist females girdle. Males
can mate with more than one female. About 87% of adults attracted
to lights were males (T=1008) (Polk and Ueckert 1973).
Each female girdles about 1 branch, although the number of
branches girdled varied in field cage trials from 0.96/female
(at 50 beetles/tree) to 1.6/female (at 10 beetles/tree) (Polk
and Ueckert 1973). Females girdle stems of ca. 5-20mm in diameter
(measured immediately above the girdle; mean 9mm+/-0.05; 10mm+/-0.06),
chewing through the periderm, nontranslocating phloem, translocating
phloem, cambium, and far enough into the xylem to prevent
upward translocation of water and nutrients. Girdling may
take at least 2 days (Polk and Ueckert 1973). Girdling always
results in death to the portion of the branch above the girdle,
although the leaves may remain on these girdled branches for
some time, apparently because no abscission zone forms (Ueckert
et al. 1971; Polk and Ueckert 1973).
Ovipositing females make an incision in the bark with their
mandibles while facing toward the base of the tree, before
turning around and inserting the egg parallel to the branch
and beneath their abdomen distal to the incision, and sealing
the incision with an amber secretion. Oviposition takes ca.
20-30 minutes for each egg. The distance between eggs varied
with the length and diameter of the branch, but they were
usually at least 40 mm apart on the branch (Polk and Ueckert
1973). The mean number of eggs laid per branch were 8.1 to
8.2 +/- 1.1 (Polk and Ueckert 1973; Ueckert et al.
1971).
97-98% of eggs hatch within 10-14 days, and larvae feed upon
the sapwood, opening the oviposition scar to expel frass after
about 3 months. Each larvae fed, with its venter towards the
bark, on only one side of the branch, severely weakening the
branch at that point. Each larvae consumes about 1.44+/-0.12cc
of wood during development (Polk and Ueckert 1973). The insect
overwinters as larvae (Ueckert et al. 1971), but it
is not known whether they diapause, nor at which instar they
are in.
Larvae "pupate" within larval galleries in late
summer (late August to early September). Pupae lasted ca.
14 days and are very mobile inside the galleries (Polk and
Ueckert 1973).
Parasites (e.g. Chalcedectidae, Pteromalidae, Eupelmidae,
Eurytomidae) and predators (e.g. Cleridae) killed 15-22% of
the larvae, while 34-55% died from undetermined causes. About
31% of all girdled branches were broken off by windstorms
and livestock before adults emerge, resulting in high mortality
of larvae from excessively high temperatures near the ground
(Polk and Ueckert 1973).
Host-specificity
Field data from the native-range suggests it could be specific
to Prosopis glandulosa, although there is an unsubstantiated
report of it damaging Leucaena leucocephala (Felker
et al. 1983). Host-specificity testing was not completed
but suggest adults can feed on a wide range of plant species,
especially in the absence of mesquite. Impact from adult feeding
is, however, likely to be negligible and data on larval host-ranges
will be critical.
Mass-rearing and release
Quarantine testing not completed. An application to release
was not submitted.
Current research
None.
|
