Diomus sp. nr subclarus (Blackburn, 1895)
Diomus mealybug ladybird
Species in the genus Diomus are difficult to identify. At present it is believed that this species may be Diomus subclarus (Blackburn, 1895), but until it can be properly confirmed the name is in doubt.
Biostatus and distribution
This adventive ladybird was first found about 2005 by Stephen Thorpe in Devonport, Auckland. It has been found feeding on endemic and adventive species of mealybugs.
Conservation status: This adventive ladybird is established in Auckland and feeds on adventive and endemic species of mealybugs.
Life stages and annual cycle
There are no detailed observations on the annual cycle of this ladybird in New Zealand. There are probably two or three generations in summer in Auckland. They probably overwinter as adults.
The adults are small, about 2.5 millimetres long and 1.5 mm wide. The female head, prothorax (first part of the middle body) and elytra (wing covers) and the underside of the body are black and covered in short pale setae (hairs). The bases of the legs are dark, but the tibia and tarsi (feet) are brown as are the antennae. The adult male has yellow on the front lateral corners of the pronotum and on the head, the area between the eyes is yellow. Under the elytra are a pair of wings used for flying. The small head has a pair of compound eyes.
Eggs are probably laid in or near colonies of mealybugs. A larva hatches from each egg. The three pairs of legs are used for walking. As the larva grows, it moults (changes skin). There are four larval instars (stages). The young larvae are yellow-brown. In older larvae the dark gut can be seen. In the last instar, there are white areas laterally on the margins of all segments and a line of white intersegmental areas on either side of the midline. These white areas produce abundant white wax on the mature larva. The wax is usually present on the larval skin at the base of the pupa. The pupa is pale tan and covered with short hairs that often have droplets at their tip. When adults hatch from pupae they remain partly in the pupal skin while the cuticle hardens and their full colour develops. The length of time of each life stage depends on temperature, being shorter at higher temperatures.
Walking and flying
Both adult and larval stages of this ladybird have three pairs of legs that can be used for walking. Adults have wings and can fly.
The adult and larval ladybirds eat mealybugs. The jaws are the primarily structures used for holding and chewing the prey. Legs do not appear to be used for holding food.
There are several species of ladybirds in New Zealand that have small black adults. They require expert knowledge for correct identification. The adult male Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) has distinctive yellow marks on its head and pronotum (segment behind the head) that are similar to those on the male yellow shouldered ladybird, Apolinus lividigaster. The yellow shouldered ladybird is larger, 3-4 mm long compared to male Diomus mealybug ladybird (2.2-2.5 mm long). Yellow shouldered ladybirds are only associated with aphids, while Diomus mealybug ladybirds are only associated with mealybugs.
The larvae of the Diomus mealybug ladybird are unlike any species currently known in New Zealand, especially those associated with mealybugs. However, there are several species of ladybirds with similar looking pupae.
No natural enemies of Diomus mealybug ladybirds are known in New Zealand. They are probably preyed upon by birds, spiders and predatory insects.
Adults and larvae of Diomus mealybug ladybird feed on mealybugs (Hemiptera: Pseudococcidae) that live on toetoe, Austroderia splendens, New Zealand flax, Phormium tenax and Hibiscus sp.
|Scientific Name||Common Name||Classification||Reliability Index||Biostatus|
|Balanococcus danthoniae (Morrison, 1925)||Hemiptera: Pseudococcidae||10||endemic|
|Balanococcus diminutus (Leonardi, 1918)||New Zealand flax mealybug||Hemiptera: Pseudococcidae||10||endemic|
|Paracoccus glaucus (Maskell, 1879)||Long egg-sac mealybug||Hemiptera: Pseudococcidae||10||endemic|
|Pseudococcus longispinus (Targioni Tozzetti, 1867)||Long-tailed mealybug||Hemiptera: Pseudococcidae||10||adventive|
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).
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.
Alan Flynn for identification of the ladybird.
Stephen Thorpe for information about the ladybird.
1 November 2018. NA Martin. Changed symbol used for apostrophes.