''Nematus spiraeae'' is a species of

sawfly Sawflies are the insects of the suborder Symphyta within the order Hymenoptera, alongside ants, bees, and wasps. The common name comes from the saw-like appearance of the ovipositor, which the females use to cut into the plants where they lay ...

in the family

Tenthredinidae Tenthredinidae is the largest family of sawflies, with well over 7,500 species worldwide, divided into 430 genera. Larvae are herbivores and typically feed on the foliage of trees and shrubs, with occasional exceptions that are leaf miners, stem ...

, known as the aruncus sawfly and sometimes the spiraea sawfly. It is native to central and northern Europe and was first recorded in Britain in 1924. Its larvae feed on the leaves of goat's beard (''Aruncus dioicus'').

Description

The adult aruncus sawfly is between long. The antennae, head and thorax are brownish-black and the abdomen yellowish-brown, the underside being paler than the upper side. The wings are membranous with brown veins and the tegulae are pale-coloured. Larvae grow to long; they are a translucent green and have short, pale hairs growing from low warts. The head is greenish-brown to brown. Eggs are capsule-shaped, white and about long.

Life cycle

Aruncus sawflies are all females, breeding by

parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...

. The adults emerge in late spring and

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

s are laid on the underside of the leaves of goat's beard (''Aruncus dioicus'') shortly afterwards. Eggs hatch a week later, releasing gregarious larvae, which consume leaf tissue between the main veins.

Metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

occurs after four or five weeks in the soil, each pupa protected by silken cocoons. Adults emerge in late July and August producing a second generation of larvae, and occasionally a third generation. Those larvae descend to the ground late in the year, overwinter as pre-pupae, and pupate in the spring.

Damage and control

In heavy infestations, leaves may be skeletonized except for their main veins, and the plants may become completely defoliated. The larvae can be picked off by hand, or in heavier infestations, chemical pesticides can be used. Organic products such as

pyrethrum ''Pyrethrum'' was a genus of several Old World plants now classified as ''Chrysanthemum'' or ''Tanacetum'' which are cultivated as ornamentals for their showy flower heads. Pyrethrum continues to be used as a common name for plants formerly inclu ...

will control small larvae but more powerful synthetic insecticides are needed when the larvae are large.

References

External links

* {{Taxonbar, from=Q14582391 Tenthredinidae Agricultural pest insects Insects described in 1883 Taxa named by Ernst Gustav Zaddach Hymenoptera of Europe