INTERESTING INSECTS

By N A Martin (2016)

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.

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.

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.

Feeding

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.

Adult female Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZZ]

Underside of an adult female Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZY]

Adult male Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae), note the yellow on the head and pronotum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZW]

Underside of an adult male Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae), note the yellow on the head and pronotum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZV]

Side view of an adult female Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZB]

A young larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZK]

Two larvae of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DYU]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZ7]

Young larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) feeding on a mealybug (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZ9]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZ2]

Underside of larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZ1]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DYT]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZC]

Prepupal larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZ4]

Prepupal larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZF]

Pupa of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DYZ]

Pupa of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZU]

Pupa of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZH]

Adult Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) emerging from pupa. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZS]

Pupal skin of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2E00]

Method of rearing Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) on flax leaves. The clips prevent the leaves rolling and hiding or crushing the ladybird larvae and pupae. The white arrow points to a ladybird larva. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZX]

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.

Adult female Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) on leaf of toetoe, Austroderia splendens, with Balanococcus danthoniae (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZ5]

Adult male Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) on leaf of New Zealand flax, Phormium tenax, with Balanococcus diminutus (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZA]

Adult female Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZP]

Underside of an adult female Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZN]

Adult male Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae), note the yellow on the head and pronotum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZW]

Underside of an adult male Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae), note the yellow on the head and pronotum. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZV]

Adult male yellow shouldered ladybird, Apolinus lividigaster (Coleoptera: Coccinellidae), front view showing yellow head. Creator: Tim Holmes. © Plant & Food Research. [Image: 2E1D]

Side view of an adult male yellow shouldered ladybird, Apolinus lividigaster (Coleoptera: Coccinellidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2E1C]

Young larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) feeding on a mealybug (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZ8]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZC]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DYX]

Underside of larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DYW]

Prepupal larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) in mealybug colony. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DYV]

Prepupal larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZF]

Side view of a pupa of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DYY]

Pupa of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZG]

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.

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) in a colony of Balanococcus danthoniae (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DYS]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) feeding on a mealybug, Balanococcus danthoniae (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZ3]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) in a colony of mealybugs (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZE]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) in a colony of long-tailed mealybug, Pseudococcus longispinus (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZI]

Larva of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) feeding on a long-tailed mealybug, Pseudococcus longispinus (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZM]

Pupa of Diomus mealybug ladybird, Diomus sp. nr subclarus (Blackburn, 1895) (Coleoptera: Coccinellidae) in colony of mealybugs (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2DZT]

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.