Flowering currant

Small (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leaves. They excrete sticky honeydew. The diagnostic feature that distinguishes aphids from other small sucking insects is the pair of siphunculi (tubular projections) at the rear of the abdomen together with a tail-like cauda; a single colony usually holds wingless forms (parthenogenetic females) alongside winged migrants that fly onto new plants in summer. In summer aphids reproduce parthenogenetically and viviparously over many generations, so the population builds up explosively; in autumn many species produce a sexual generation that lays overwintering eggs on the host, and host-alternating species move between a winter host (often a tree or shrub) and a summer host (a herbaceous plant). Feeding symptoms include curling, crinkling and distortion of young leaves, stunted growth, yellowing, and the shedding of buds and fruitlets. Abundant honeydew coats the leaves, and the sooty mould fungus that develops on it forms a black film which limits photosynthesis; the honeydew is fed on by ants, which in return defend the colony against predators. Aphids are also important vectors of plant viruses (mosaics among them), transmitting them from plant to plant even during a brief probing puncture.

The larvae strongly resemble the caterpillars of butterflies and moths, but have more pairs of abdominal prolegs (six and more) and single ocelli on the sides of the head, by which they can be told apart. They often feed gregariously, skeletonising the leaves or eating them down to the veins, and can strip a gooseberry or currant bush bare within a few days. The host plants are gooseberry, currant, rose, plum and pine. Symptoms: besides the defoliation of leaves, the larvae of fruit-dwelling species (e.g. on plum) bore into the young fruit set and cause it to drop. Adult sawflies are small (a few millimetres) hymenopterans without a distinct 'wasp waist' — the abdomen is broadly joined to the thorax, which distinguishes them from wasps and bees; the females have a saw-like ovipositor (hence the name 'sawflies'), with which they cut into the tissue of a leaf or fruit set and lay their eggs inside it. The larvae are most often green, matching the colour of the leaf, in some species with dark warts or spots; their prolegs lack the grasping crochets that the caterpillars of moths have, and when disturbed the larvae of many species raise the rear end of the body into a characteristic 'S' shape. The most damaging groups are: the gooseberry sawfly (Nematus ribesii) on gooseberry and currant, stripping the bush from the inside out; the slug sawflies (genus Caliroa) on pear, cherry and plum, whose slimy, slug-like larvae graze away the upper skin of the leaf (windowing), so that the leaf turns brown as if scorched; the fruit sawflies of the genus Hoplocampa on plum and apple, tunnelling galleries into the young fruit set and leaving moist, foul-smelling droppings; and the conifer sawflies (Diprion, Neodiprion) on pine, feeding gregariously on the needles. Life cycle: the adults emerge in spring, the larvae feed for several weeks, after which they descend into the soil or leaf litter, where they pupate in a cocoon and overwinter as a larva (prepupa); depending on the species, 1–3 generations develop in a season.