Rhyzobius lophanthae (Blaisdell, 1892)
POLYPHAGA Emery, 1886
CUCUJOIDEA Latreille, 1802
COCCIDULINAE Mulsant, 1846
Rhyzobius Stephens, 1829
Native to Queensland and Southern Australia, this species has been introduced into many countries as a biocontrol agent of various scale pests and is now established in all but the colder northern regions throughout the world. For various reasons it is ideal control agent and once established the species tends to spread rapidly; adults are fecund and long-lived, they do not diapause and, outside of their native range, they generally lack parasites, and under good conditions there are five to seven generations each year. The species seems to be widely established in Europe; in some regions it has been present since the early 20th century e.g. it was first recorded from Sicily in 1908, but many records suggest a much more recent northern expansion e.g. it was first recorded from France in 1975 and from Germany in 1993. The first UK record was from Surrey in 1999 and since that time it has become established and spread throughout Southern England and the Midlands although it remains absent from most of Wales. The species is a natural predator of various scale insects; it has been used specifically to control Oleander Scale (Aspidiotus nerii Bouché, 1833), Tortoise Wax Scale (Ceroplastes japonicus Green, 1921), Circular Scale (Chrysomphalus aonidum (Linnaeus, 1758)), Dictyospermum Scale (C. disctyospermi (Morgan, 1889)) and San José Scale (Quadraspidiotus perniciosus Comstock, 1881) among others on a wide range of commercial fruits etc. worldwide, but more generally it is thought to be able to predate most scale insects. Adults occur year-round, they are able to survive UK winters and remain active in all but the coldest spells; they tend to be most prolific during late summer and autumn but can be beaten from trees and shrubs at any time. The typical habitats are wooded areas of parks and gardens, especially where conifers are present (they seem to like Leyland Cypress and Juniper hedges), but any wooded areas are likely to host them. Both adults and larvae predate scale insects, especially armoured scales (Hemiptera, Diaspididae) although they have also been observed feeding on Mealybugs (Hemiptera, Pesudococcidae) and other soft insects. Little is known of the life cycle in the UK, but more generally mating occurs throughout the warmer months and all stages have been observed to overwinter. Females search out scale insect colonies and lay batches of eggs among them or under scale covers. Freshly emerged larvae crawl under adult scale insects and feed
Rhyzobius lophanthae 1
Rhyzobius lophanthae 2
on any small nymphs present before they have a chance to disperse, they then move between the scales, consuming nymphs and eggs as they go. Fourth (final) stage larvae feed externally, taking eggs and nymphs, and it is this stage that consumes most of the prey. Pupation occurs on the surface of leaves, the oval and orange or pink pupa retaining the shed larval skin on its abdomen. Adults can live for up to a year but the usual length is about 100 days, under good conditions the life cycle lasts between 27 days (at 30°C) and 87 days (at 15°C). Females can produce more than 500 eggs over their lifetime, depending on temperature and nutrition. Because of its value in pest control there is a great deal of information available online, including pictures of early stages, and cultures of adults are available for purchase from several sites.
1.7-2.9 mm. Broadly-oval and very convex, dorsal surface with fine and moderately long pubescence throughout, body bicoloured; forebody, underside and appendages reddish (pronotum sometimes partly darkened), elytra dark grey or black, often with a faint metallic sheen. Distinguished from our other pubescent species by the overall colour, coarsely-faceted eyes and long antennae which reach back to the pronotal base. Our other ‘dark’ Rhyzobius, R. forestieri, has the body entirely dark and is always unmetallic. Head flat between convex and very prominent eyes, anterior margin of labrum evenly curved, antennae with a long and slender four-segmented club. Pronotum transverse, lateral margins more strongly curved from the middle to rounded anterior angles, posterior angles slightly obtuse and basal margin produced towards the centre, surface finely punctured throughout. Elytra broadly-oval, convex and evenly curved from rounded shoulders to a continuous apical margin, surface randomly punctured throughout, a little more strongly so than the head and pronotum.