Agriculture Reference
In-Depth Information
entirely black.
Larva
up to 18 mm long;
body
green, speckled with black;
head
yellowish-green
to greyish-green.
avidly on ripening or over-ripe apples, grapes,
pears, plums and other fruits, especially those
previously damaged by birds or other agents;
wasps thereby become a nuisance. The presence
of such insects in fruit plantations at harvest is
also a potential hazard to fruit pickers, even
when the insects are foraging only on fallen
fruits. Wasps are sometimes also a problem in
flower borders and nurseries, where they may
remove tissue from the stems of woody plants
such as garden dahlia; injured plants often then
collapse. This plant material, in common with
that removed from wooden posts, shed walls,
etc., is used in nest construction. Although much
maligned, wasps are also beneficial insects, as
they prey during the spring and summer on
harmful caterpillars and other pests that are then
fed to their developing brood.
Family FORMICIDAE (ants)
Lasius
spp.
In the tropics and subtropics, ants are of consid-
erable economic importance and various species
cause considerable damage to cultivated plants.
Ants are far less significant in temperate regions,
although
Lasius fidiginosus
(Latreille) and mem-
bers of the genus
Camponotus
Mayr are consid-
ered forestry pests in continental Europe.
In Britain, ants (especially the yellow meadow
ant,
L. flavus
(F.)) sometimes damage potato tu-
bers, causing a noticeable pitting of the surface;
the pits sometimes coalesce to become distinc-
tive surface depressions. Such attacks occur
mainly in gardens and allotments, and are most
often noticed in July and August. Under dry
spring conditions, ants will also cause slight dam-
age to ornamental trees and shrubs (and also to
fruit trees, especially apple); they either bite into
the soft, young tissue of the buds and unfurling
leaves or sever the stamens of open blossoms in
their attempts to reach the nectaries and imbibe
nectar. Most frequently, however, worker ants
ascend trees and shrubs to collect honeydew ex-
creted by aphids and other pests; such ants will
'defend' aphid colonies from attacks by natural
enemies. Subterranean activities by ants are, oc-
casionally, a problem to horticulturists, as the
insects accidentally disturb seeds, seedlings and
older plants; invasion of stored compost by ants
is also an unwelcome inconvenience.
BIOLOGY
Vespid wasps are social insects, with three dis-
tinct castes: queens, workers and males. Young,
fertilized queens overwinter and eventually
emerge in the spring. Each soon begins to search
for a suitable nesting site, such as a hollow tree
or a dry, underground cavity in the soil. A
wasp's nest is formed from grey (as in
Vespula
germanica),
brown or yellow (as in
V. vulgaris),
masticated wood pulp and contains numerous
papery cells in each of which an egg is laid and a
larva reared. As the season progresses, new cells
are constructed and further eggs are deposited.
The colony increases rapidly in size, especially
after the first young adult worker wasps have
emerged and aid the mother queen in the task of
tending the brood. Workers also eventually take
over all foraging duties; this allows the queen to
remain within the comparative safety of the nest.
Although adult wasps feed mainly on sugary sub-
stances, their larvae are fed mainly on dead in-
sects. A successful colony may contain several
thousand individuals and, at the height of its de-
velopment, the nest will have reached the size of
a football. At this stage, males and new queens
are reared. These young queens, usually having
mated in the field with males from other colo-
nies, soon hibernate. As autumn approaches,
wasp colonies gradually decline and the ageing
Family VESPIDAE (wasps)
Vespula germanica
(F.)
German wasp
Vespula vulgaris
(L.)
Common wasp
Wasps are generally abundant, well-known in-
sects and are often regarded as pests. They feed
