PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Citrus gall wasp
An example of a gall wasp
Scientific name
A native wasp (Bruchophagus fellis, Eurytomidae,
Order Hymenoptera) infests citrus in Queensland,
NSW, Victoria and South Australia. Another gall
wasp (Eurytoma sp.) has recently been found to
also attack some citrus.
Host range
Citrus. Citrus gall wasp is native to coastal NSW
and Qld where it develops in the native finger lime
(Microcitrus australiasica). All citrus can be
attacked, but there are differences in susceptibility.
Description & damage
Damage is caused by the larvae.
Adult wasps are black, about 3 mm long, they
are smaller than the length of a match. Larvae,
when fully grown are white, about 3 mm long,
legless, tapering towards each end of the body.
Stems. Injury is caused by the female wasps
depositing eggs within the stem and subsequent
feeding and development of wasp larvae which
causes extensive galling. The galls may be up to
25 cm long and 3 cm thick containing hundreds of
larvae. Old galls are covered with the small
emergence holes of the adult. Twigs. In spring
heavily flecked young twigs indicate that citrus
gall wasps are laying large numbers of eggs in the
current spring growth. Twigs may die and be
replaced by weaker growth.
Leaf midribs, petioles & fruit stems.
Although stems are most frequently attacked,
these parts may also be infested.
General. Damage is very serious in nursery
stock as the main stem may be attacked. Heavy
galling weakens older trees and may reduce
fruiting. Fungal diseases, eg melanose, may
invade dead tissues and cause further damage.
Diagnostics.
Galls are quite distinctive (Fig. 91 below).
Do not confuse male citrus gall wasps (black
on top and brown underneath) with parasitic
native female Magastigmus wasps which are
honey coloured, and about the same size.
Lucid key What Wasp is That?
www.cbit.uq.edu.au/software/whatwasp/
Pest cycle
There is a complete metamorphosis (egg,
larva (4 stages), pupa and adult) with 1 generation
each year. Adult wasps emerge from tiny exit holes
on galls in spring, mate and females immediately lay
eggs, after which they live only about a week.
Young twigs only a few weeks old are selected for
egg laying usually on the same tree. Each female
deposits more than 100 eggs between bark and
wood. Larvae hatch from eggs and feed within plant
tissues during summer, autumn and winter to early
spring when they pupate in the galls.
Fig. 91. Citrus gall wasp
(Bruchophagus fellis). PhotoNSW
Dept of Industry and Investment (E.H.Zeck).
1. Eggs (x 24)
2. Larvae
3. Pupa
4. Adult wasp
5. Emergence holes of adults
(all enlarged x 12)
6. Galled lemon twig showing
exit holes of adult wasps
7. Gall cut open to show cells
in which wasp develops
8. Adult wasps laying eggs
(all actual size)
Insects and allied pests - Hymenoptera (ants, bees, sawflies, wasps) 121