Native mealybug ladybird - Rhyzobius sp. 1
By N A Martin (2016)
The Native mealybug ladybird, Rhyzobius sp. 1 was first recognised as a distinct species in a 1990 publication by Dr. Willy Kuschel about his survey of beetles in Lynfield, Auckland. The ladybird is awaiting scientific description and naming.
Biostatus and Distribution
This small unnamed endemic ladybird has only been found in regenerating coastal native forest by the Manukau Harbour and Auckland’s West Coast. It feeds on mealybugs, notably the long-fringed Astelia mealybug, Rastrococcus asteliae (Maskell, 1884) (Hemiptera: Pseudococcidae), an endemic species and has been found on found on Astelia banksii, one the of the mealybugs host plants.
Conservation status: The status of this uncommon ladybird is unknown.
Life Stages and Annual Cycle
The adult ladybirds are small, about 2 millimetres long. The head, prothorax (first part of the middle body) and elytra (wing covers) are yellow-brown with two pairs of dark patches on the elytra. The body and elytra are covered by short pale setae (hairs). The legs and underside of the body are yellow-brown. Under the elytra is a pair of wings used for flying. The small head has a pair of compound eyes, two short antennae and two palps.
Female ladybirds lay eggs, probably in colonies of mealybugs. A larva hatches from each egg. There are three pairs of legs that are used for walking. As the larva grows, it moults (changes skin). There are four larval instars (stages). The larvae look a little like mealybugs, a yellow body covered in areas of white wax with what appears to be short wax setae on the tubercles. The small head is pale brown.
When the fourth larval instar is fully grown, it attaches itself to a sheltered place on the plant and moults into a pupa. The bright yellow pupa is covered with short setae. The moulted larval skin remains at the base of the pupal abdomen. When the adult hatches from pupae it is bright yellow. It stays in the split pupal skin for several days and darkens in colour and most develop the dark patches on the elytra. 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 are at least two generations per year, October to December, January to April. There could be up 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 can be used for walking. Adults have wings and can fly.
The adult and larval ladybirds eat long-fringed Astelia mealybugs, Rastrococcus asteliae (Maskell, 1884) (Hemiptera: Pseudococcidae) and other species of mealybugs. The jaws are the primarily structures used for holding and chewing the prey. Legs do not appear to be used for holding food.
Although there are several small Rhyzobius species in New Zealand, the adult Native mealybug ladybird, Rhyzobius sp. 1 (Kuschel 1990), is distinctively coloured, which enables it to be identified. The body is relatively long and narrow. The head, prothorax (first part of the middle body) and elytra (wing covers) are yellow-brown and most have two pairs of dark patches on the elytra. The body and elytra are covered by short pale setae (hairs). The legs and underside of the body are yellow-brown.
The appearance of larvae and pupae of only a few of the Rhyzobius species in New Zealand are known. Those of the Native mealybug ladybird are distinctive and may enable identification of the species. The larvae look a little like mealybugs having a yellow body covered with white wax. The pupa is bright yellow and covered with short setae.
No natural enemies of the Native mealybug ladybird are known in New Zealand. They are probably preyed upon by birds, spiders and predatory insects.
Adults and larvae of Native mealybug ladybird feed on mealybugs. Larvae were first found feeding on the long-fringed Astelia mealybug, Rastrococcus asteliae (Maskell, 1884) (Hemiptera: Pseudococcidae). The ladybird has since been found on leaves of kawakawa, Piper excelsum feeding on long egg-sac mealybugs, Paracoccus glaucus (Maskell, 1879).
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).
Kuschel G. 1990. Beetles in a suburban environment: A New Zealand case study. DSIR Plant Protection Report. No. 3: 1-118.
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.