Scale-eating ladybird - Rhyzobius fagus
By N A Martin (2016)
Scymnus fagus Broun, 1880,
Rhyzobius erythrogaster Lea, 1929,
Rhyzobius kingensis Lea, 1908,
Rhyzobius nigrovatus Bielawski, 1973,
Rhyzobius satelles Blackburn, 1892
Three Australian species, Rhyzobius erythrogaster Lea, 1929, Rhyzobius kingensis Lea, 1908, Rhyzobius satelles Blackburn, 1892 and one from New Caledonia, Rhyzobius nigrovatus Bielawski, 1973 have been synominised with Rhyzobius fagus (Broun, 1880) (Tomaszewska, W. 2010. Rhyzobius Stephens, 1829 (Coleoptera: Coccinellidae), a revision of the world species. Fauna Mundi Warszawa, Museum and Institute of Zoology, Polish Academy of Sciences 2: 475 pp.).
Biostatus and Distribution
Until recently the Scale-eating ladybird, Rhyzobius fagus was believed to be found only in New Zealand, but a recent taxonomic revision means that the species is also present in Australia and New Caledonia and is therefore native to New Zealand. In Auckland the ladybird is often seen feeding on Flocculent flax scale, Poliaspis floccosa Henderson, 2011 (Hemiptera: Diaspididae) and recently found feeding on a species of felted scale insect (Eriococcidae). It also feeds on pest scales in the armoured scale family, Diaspididae. The ladybird can be found in orchards, parks, gardens and native habitats.
Conservation status: This ladybird is widespread
Life Stages and Annual Cycle
The adult ladybirds are small, about 2.5 millimetres long. The head, prothorax (first part of the middle body) and elytra (wing covers) are black, and covered in short pale setae (hairs). The legs are black, except the tarsi (feet) which are brown like the antennae and mouthparts. The underside of the abdomen is brown, though the underside of the thorax is either brown or black. Under the elytra is a pair of wings used for flying. The small head has a pair of compound eyes and two short antennae.
Female ladybirds lay eggs probably near colonies of scale insects. A larva hatches from each egg. The three pairs of legs are used for walking. They do not appear to be used for holding prey. As the larva grows, it moults (changes skin). There are four larval instars (stages). The last instar has areas of black and pale brown. The thorax is pale with dark central areas of the mesonotum and metanotum (body segments with the 2nd and 3rd pairs of legs), while the first four abdominal segments are pale centrally and the remaining abdominal segments are pale laterally. The tubercles bearing setae are pale brown or grey. The larva has long lateral seta and produces wax at the base of the setae on the tubercles. The small head is dark brown.
When the fourth larval instar is fully grown, it attaches itself to a sheltered place on the plant and produces more white wax before it moults into a pupa. The pale, tan pupa is covered with short setae and fewer longer hairs bearing droplets. The moulted larval skin remains at the base of the pupal abdomen. Adults hatch from pupae and mate. The length of time of each life stage depends on temperature, being shorter at higher temperatures.
Preliminary observations on this ladybird’s annual cycle in Auckland indicates that there is a generation from December - February and another from March to May or November. There could be two to four generations a year in Auckland. The ladybird probably overwinters as adults.
Walking and flying
Both adult and larval stages of this ladybird have three pairs of legs that are used for walking. The larva also uses the tip of its abdomen to hold onto the plant surface. Adults have wings and can fly.
The adult and larval ladybirds eat scale insects in two families, armoured scale (Diaspididae) and felted scale (Eriococcidae). The jaws are the primarily structures used for holding and chewing the prey. Legs do not appear to be used for holding food. The ladybirds feed on the ‘naked’ scale insects and can chew through the covering of armoured scales and the felted scales.
Larvae of Scale-eating ladybird, Rhyzobius fagus (Coleoptera: Coccinellidae) in a colony of flocculent flax scale, Poliaspis floccosa (Hemiptera: Diaspididae); note the recently moulted larva (top left) with the pale head and pronotum, and its nearby moulted skin. Image: Tim Holmes © Plant & Food Research
There are several small black Rhyzobius species in New Zealand and expert knowledge is required to name them. However, small black ladybird adults on New Zealand flax leaves that are infested with flocculent flax scale, Poliaspis floccosa (Hemiptera: Diaspididae), are likely to be the Scale-eating ladybird, Rhyzobius fagus, because it is the only species of black ladybird known to feed on this scale insect.
The appearance of larvae and pupae of only a few of the Rhyzobius species in New Zealand are known. Although the larvae and pupae of this Scale-eating ladybird appear to be distinctive, it is not known if they can be reliably distinguished from those stages of all other Rhyzobius species. Adults need to be reared and the adults identified.
The last instar (stage) larva has areas of black and pale brown. The thorax is pale with dark central areas of the mesonotum and metanotum (body segments with the 2nd and 3rd pairs of legs), while the first four abdominal segments are pale centrally and the remaining abdominal segments are pale laterally. The tubercles bearing setae are pale brown or grey. The larva has long lateral seta and produces wax at the base of the setae on the tubercles. The pupa is pale tan and covered with short setae and fewer longer hairs bearing droplets. It is similar to the pupa of other ladybirds.
No natural enemies of the Scale-eating ladybird, Rhyzobius fagus, are known in New Zealand. They are probably preyed upon by birds, spiders and predatory insects.
A mite that is a parasite of scale insects, Hemisarcoptes coccophagus (Acari: Hemisarcoptidae), has a juvenile stage, deutonymph, that may temporarily attach itself to adult ladybirds that feed on armoured scale insects (Hemiptera: Diaspididae). The mite uses the ladybird to take it to other colonies of scale insects. Deutonymphs of this mite are carried by adult Scale-eating ladybird, Rhyzobius fagus. This behaviour is called phoresy and is generally harmless to the ‘host’ insect.
Adults and larvae of Scale-eating ladybird, Rhyzobius fagus, feed armoured scale insects (Hemiptera: Diaspididae) and felted scale insects (Hemiptera: Eriococcidae). Armoured scale insects are easily recognisable because their soft bodies are covered in a hard waxy covering that is secreted by the insect. Most adult female felted scale insect, and the prepupal male felted scale insect cover themselves with a distinctive felted material.
Adults and larvae of the ladybird are commonly seen on flax leaves feeding on the flocculent flax scale, Poliaspis floccosa Henderson, 2011, where they compete with the Flax scale-eating caterpillar, Batrachedra arenosella (Walker, 1864) (Lepidoptera: Batrachedridae). A ladybird larva that looked like that of the Scale-eating ladybird was seen in a colony of another Poliaspis species and another was seen feeding on the native fern scale, Fusilaspis phymatodidis (Maskell, 1880). The ladybird has also been found to prey on species that are pests of crops, e.g. Greedy scale, Hemiberlesia rapax, and Lantania scale, Hemiberlesia lataniae, that are found in kiwifruit orchards on vines and shelter trees.
Ladybird larvae have also been found and reared on one species of felted scale, Eriococcus fulgitectus Hoy, 1962, living on leaves of a small tree of Ngaio, Myoporum laetum G.Forst. (Scrophulariaceae).
|Scientific Name||Common Name||Classification||Reliability Index||Biostatus|
|Eriococcus fulgitectus Hoy, 1962||Hemiptera: Eriococcidae||9||endemic|
|Fusilaspis phymatodidis (Maskell, 1880)||Fern scale||Hemiptera: Diaspididae||9||endemic|
|Hemiberlesia lataniae (Signoret, 1869)||Latania scale||Hemiptera: Diaspididae||9||adventive|
|Hemiberlesia rapax (Comstock, 1881)||Greedy scale||Hemiptera: Diaspididae||8||adventive|
|Poliaspis floccosa Henderson, 2011||Flocculent flax scale||Hemiptera: Diaspididae||10||endemic|
Diverse habits of ‘ladybirds’
Not all ladybirds eat insects; some feed on mites. Other species eat plant leaves and are pests especially in some tropical countries, whereas other ladybirds feed on fungi. One of these, Illeis galbula (Mulsant, 1850), from Australia, feeds on powdery mildew fungi. In New Zealand, it is common on pumpkins and other cucurbits, plants that are commonly infected by powdery mildews. A plant feeding ladybird, hadda beetle (Epilachna vigintioctopunctata (Fabricius, 1775)) recently established in Auckland feeds on plants in the Solanaceae (potato family).
Biological control of pests
Biological control of scale insects and other herbivorous pests can reduce the impact of the pests on crops and reduce the need to use insecticides. The Scale-eating ladybird, Rhyzobius fagus is a predator of some species of armoured scale insects, (Hemiptera: Diaspididae) that are pests of Kiwifruit and the shelter trees that surround the orchards. The adult ladybirds may also carry a parasitic mite, Hemisarcoptes coccophagus (Acari: Hemisarcoptidae), to new colonies of the scale insects. If pesticides are needed to control other pests, it is advisable to use chemicals that will have minimal harmful effects on the ladybirds or to use them at a time when the ladybirds are not present.
Hill G, Charles JG, Lupton TS, Logan DP, Allan DJ. 2007. Releases from 1994-1997 and rediscovery of the parasitic mite Hemisarcoptes coccophagus Meyer (Acari: Hemisarcoptidae) in Gisborne and Bay of Plenty. New Zealand Entomologist. 30: 63-70
Hill MG, Allan DJ, Henderson RC, Charles JG. 1993. Introduction of armoured scale predators and establishment of the predatory mite Hemisarcoptes coccophagus (Acari: Hemisarcoptidae) on lantania scale, Hemiberesia lataniae (Homoptera: Diaspididae) in kiwifruit shelter trees in New Zealand. Bulletin of Entomological Research. 83: 369-376
Tomaszewska, W. 2010. Rhyzobius Stephens, 1829 (Coleoptera: Coccinellidae), a revision of the world species. Fauna Mundi Warszawa, Museum and Institute of Zoology, Polish Academy of Sciences 2: 475 pp.
Allan Flynn for identification of the ladybird.
Garry Hill for useful comments on the manuscript.
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs