Brown scale insect

A garden ant stimulated this scale insect to produce honeydew with her antenae. Some these scale insects, Parthenolecanium corni, are growing on a grapevine branch, just under strips of bark. They are about 5 mm, dark and shiny, with ridges across. When young, they are tiny and mobile and are called crawlers, and live under leaves. When they are ready to moult into the immobile scale stage they move into branches. Scale insects, as aphids, suck the sap of plants, and excrete a sugar rich liquid call honeydew, which ants like.

 These scale insects can become a pest of various fruit trees. The scale insect has natural enemies, though. Parasitoid wasps inject their eggs into the scale insect, and the larvae will emerge though holes in the scale, instead of the crawlers. A parasitised scale insect after the wasps emergence is shown below.

26/12/2011

Horse chestnut scale insect

From April to July, tree trunks and branches in our street become mottled with Horse Chestnut scale insects. The bright white, powdery substance under the 'scale' is the ovisac, loaded with thousands of eggs. The scale is the dead body of the female, which has invested her effort into the production of the ovisac, after months of feeding on tree sap, and whose function is now protect the ovisac. The Horse Chestnut scale insect, Pulvinaria regalis, is an invasive species from Asia found in the early 60s and described from specimens in Paris in 1968. It is a generalist species, found mainly in urban environments and feeds on a diverse array of deciduous trees, and has a liking for Sycamore and Maples, Lime and Bay leaf tree.
  Scale insects do not look much like insects, do they? What we called scale insects are adult females, with flattened shiny bodies hiding tiny legs underneath, and piercing mouth parts like a shieldbug (scale insctsct are homopterans). Pulvinaria regalis has some mobility before egg laying. Both the first nymph instar (called crawlers) and adult males look more like a typical insect.
 Horse Chestnut scale insects hatch in summer and move onto the underside of leaves, where they feed.  Then, before leaf fall, they move back to the tree trunks and branches. In spring, mature males and females appear. Mature males are winged but do not feed, so they spend their short lives looking for females and mating. Females crawl to leaves, mate and start feeding on the tree sap and when fully mature and ready to lay, they move onto tree trunks to lay their ovisac. Although they can appear in such large numbers, they do not obviously cause much harm to mature trees, although saplings or weak trees may suffer from loss of sap. Scale insects, in particular eggs and nymphs, are the main food source for some ladybird species such as Exochomus quadripustulatus, the Pine Ladybird, no wonder they are also common on our street.

More information
GB non native fact sheets

Pine ladybirds waking up

 We spotted lots of Pine Ladybirds, Exochomus quadripustulatus, in our street today. They were crawling on tree trunks on the sunny side of the street, a couple of pairs mating, some still in a little group overwintering together and others just stretching their legs. They used to live mostly near pine trees, willows and sallows, but pine trees are very scarce in our area and I haven't seen any in our street. I assume in our street they feed mainly on scale insects, in particular the Chestnut Scale insect, Pulvinaria regalis, which feeds on trees, including Lime and Sycamore, producing occasionally heavy infestations. Some colour forms of the Harlequin can be similar to the Pine Ladybird, but there are always white marks on the Harlequin pronotum, while the Pine ladybird is all black, with 2 or 4 red spots, the frontal ones with a characteristic comma shape. Pine ladybirds are also smaller, 3-4 mm, and have a rim in their elythra reminiscent of a bowler hat as you can see in the photo below.