Karo felted scale ladybird - Rhyzobius acceptus
By N A Martin (2016)
Biostatus and Distribution
Karo felted scale ladybird is an endemic species. It is associated with native forest, but little is known about its distribution and habits. It has only been found feeding on one insect, a species of felted scale (Hemiptera: Erriococcidae) that lives on karo, Pittosporum crassifloium (Pittosporaceae).
Conservation status: Little is known about this ladybird.
Life Stages and Annual Cycle
The adult ladybirds are small, about 2.5 millimetres long. The head is black and covered with short fine hairs (setae). The prothorax (first part of the middle body) and elytra (wing covers) are black and white, and covered in short setae (hairs). There is a small pale area on the front lateral corner of the pronotum and large pale areas on the elytra. The legs are pale with a darker area at the base. The antennae are brown and clubbed. The underside of the abdomen is brown, varying from dark to medium. Under the elytra is a pair of wings used for flying. The small head has a pair of compound eyes and two short antennae that are clubbed and a pair of palps with broad ends.
Female ladybirds lay eggs probably near colonies of karo felted 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). In the last instar the background colour is dark grey with prominent areas of white. The centre of the mesothorax and metathorax (2nd & 3rd thoracic segments) have a central white area. The lateral areas of these segments and the abdominal segments are as white as the centre of the first, sixth and seventh abdominal segments. The pronotum (1st thoracic segment) is pale at front and the head is mottled pale and dark. Younger larvae are a paler grey, but show the beginnings of the darker and paler areas.
When the fourth larval instar is fully grown, it attaches itself to a sheltered place on the plant and produces white wax on the pale areas before it moults into a pupa. The pale, tan pupa is covered with short setae. 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. The may be earlier and later generations. 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 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 the felted scales.
There are several small black Rhyzobius species in New Zealand that have pale markings. The pale markings on this species appear to be sufficiently distinctive to enable identification by non-experts.
The appearance of larvae and pupae of are known for only a few of the Rhyzobius species in New Zealand. Although the larvae and pupae of this karo 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. Larvae need to be reared to adults and the adults identified.
The last instar (stage) larva has areas of black and white. The lateral areas of the 2nd and 3rd thoracic segments and the abdominal segments are pale, while there are strong white areas on the two thoracic segments and on abdominal segments 1, 6 & 7. At the prepupal stage these pale areas produce much white wax. The pupa is pale to dark tan and covered with short setae. The moulted larval skin at the base of the pupa has much white wax. The general appearance is similar to the pupa of other ladybirds.
No natural enemies of the Karo felted scale ladybird, Rhyzobius acceptus, are known in New Zealand. They are probably preyed upon by birds, spiders and predatory insects.
Adults and larvae of the karo felted scale ladybird, Rhyzobius acceptus, have only been found feeding on felted scale (Hemiptera: Eriococcidae) on karo, Pittosporum crassifloium (Pittosporaceae). Only one species of felted scale, Eriococcus pallidus, has been recorded from the tree, though E. pallidus, has been found living on many other species of tree.
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).
Alan Flynn for identification of the ladybird.
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.