Nephus binaevatus (Mulsant, 1850)
Dusky lady beetle, Minute ladybird, Signal Ladybeetle
Scymnus (Sidis) binaevatus Mulsant, 1850
Nephus (Sidis) binaevatus (Mulsant, 1850)
Biostatus and distribution
This adventive ladybird was first found in New Zealand in Mount Albert, Auckland in sometime after 2000. It has since been found in Avondale. In Mount Albert it is associated with mealybugs on flax, Phormium plants. It originates in Africa and in 1922 some were released into California to help control mealybugs. It has also been found on the island of St. Helena, South Atlantic Ocean.
Conservation status: This ladybird is only known from a small area of Auckland and is associated with mealybugs on Phormium.
Life stages and annual cycle
Adult Dusky lady beetles are small, about 2 mm long, and black with two red patches near the tip of the elytra (wing covers). The elytra, head and pronotum (first part of the thorax) are covered in short setae (hairs). Under the elytra is a pair of wings used for flying. The underside of the body is mostly dark brown with paler areas. It is also covered in short setae. The three pairs of legs a pale to medium brown as are the pair of short thin antennae. The female lays small eggs by or in colonies of mealybugs. A larva hatches from each egg. It is covered with white flocculent wax and looks like a woolly mealybug. The underlying body colour is orange-brown. The three pairs of legs are used for walking. Legs don't appear to be used for holding prey. The hind end of the larva is used to hold onto the plant surface when it is walking. As the larva grows, it moults (changes skin). There are four larval instars (stages). When the fourth larval instar is fully grown, it attaches itself to a sheltered place on a plant and moults into a pupa. the pupa can wag up and down. Adults hatch from pupae and mate.
In New Zealand, the Dusky lady beetles have been found breeding in summer. There are probably at least two generations per year in Auckland. 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 the mealybug ladybirds have three pairs of legs that can be used for walking. The larva can also hold onto the plant surface with rear end of its abdomen, which acts like a sucker. Adults have wings and can fly.
The adult and larval dusky lady beetles 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 Dusky lady beetles have the typical ladybird shape, but are tiny, about 2 mm long, and black with a pair of red spots towards the tip of the elytra (wing covers). There are other small black ladybirds with red patches on the elytra and one, Loew's ladybird, Scymnus loewi, has larger red patches on the elytra and red areas on the head and pronotum (first part of the thorax).
The larvae look like mealybugs being covered in white flocculent wax. They are very mobile and the head and legs can be seen on their underside. The body of the larva of Dusky lady beetles is orange-brown and is similar to larvae of Loew's ladybird, Scymnus loewi.
The larvae of the mealybug ladybird, Cryptolaemus montrouzieri grow larger and the underlying body colour is dark. The adults are larger and quite different. The main part of the elytra is black, but the elytra tips, head and pronotum are brown.
No natural enemies of this ladybird are known in New Zealand.
In New Zealand the Dusky lady beetle has only been found feeding on New Zealand flax mealybug, Balanococcus diminutus (Hemiptera: Pseudococcidae). This mealybug lives between growing leaves where space is restricted.
In California, it is reported to feed on Citrophilus mealybug, Pseudococcus calceolariae (Maskell, 1879), while in South Africa it feeds on Planococcus ficus (Signoret, 1875), in vineards.
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).
Some kinds of mites (Acari) make use of insects and other animal, such as birds to travel to new food sources. One life stage has special structures that enable them to hold onto the transporting agent. The mites are usually more robust than normal. This method of transport is called phoresy.
Some species of mites have a larval stage adapted for phoresy. An example is the parasitic mite of scale insects, Hemisarcoptes coccophagus (Acari: Hemisarcoptidae), which is carried by ladybirds to new colonies of the scale insects. In New Zealand it is transported by the native, Scale-eating ladybird, Rhyzobius fagus (Broun, 1880).
Other species of mites only produce the phoretic female when food is short. Normally the female is less robust and more suited to rapid breeding. Examples in New Zealand include the fungal feeding mites in the subgenus, Siteroptes (Pediculaster).
The Nikau palm pollen mite, Neocypholaelaps novahollandiae Evans, 1961 (Acari: Mesostigmata: Ameroseiidae) develops phoretic females when flowering is coming to an end. The females are carried to new flowers by both birds and insects that feed on the pollen and nectar.
Adults of Dusky lady beetles, Nephus binaevatus (Coleoptera: Coccinellidae) have been found carrying phoretic mites. Go to 'other images' for pictures.
Moore D. 1988. Agents used for biological control of mealybugs (Pseudococcidae). Biocontrol News & Information 9(4): 209-225.
Walton VM, Pringle KL. 2004. A survey of mealybugs and associated natural enemies in vineyards in the Western Cape Province, South Africa. South African Journal of Enology and Viticulture 25 (1): 23-25.
Alan Flynn, Plant Health & Environment Laboratory, Auckland for identification of the ladybird and helpful comments.
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.
1 November 2018. NA Martin. Changed symbol used for apostrophes.