INTERESTING INSECTS

By N A Martin (2019)

Loew's ladybird, Dusky lady beetle, Loew's Scymnus Lady Beetle

This adventive ladybird comes from North and Central America and was first found in New Zealand in 1941 in Auckland. This small two toned ladybird present in the North Island of New Zealand.

Conservation status: This ladybird is present in Northern New Zealand and may contribute to the biological control of some species of mealybugs and other insects.

The adult ladybirds are small, about 2.0-2.2 millimetres long. The head, prothorax (first part of the middle body) and elytra (wing covers) are covered in short fine hairs. These upper surfaces are coloured black with a medium brown on the head, front lateral sides of the prothorax and the hind lateral sides of the elytra. On the elytra the brown colour may extend to the front margin of the elytra or stop halfway. The legs and antennae are pale brown. Under the elytra is a pair of wings used for flying. Like most insects, this ladybird has three pairs of legs. The small head has a pair of compound eyes and two short antennae.

Female ladybirds lay eggs probably near infestations of prey. A larva hatches from each egg. The three pairs of grey legs are used for walking. They don’t appear to be used for holding prey. As the larva grows, it moults (changes skin). There are four larval instars (stages). Older larvae are grey and coated with white flocculent wax and looks like a woolly mealybug, one group of their prey. When the fourth larval instar is fully grown, it attaches itself to a sheltered place on a plant and moults into a pupa. Adults hatch from pupae and mate. The length of time of each life stage depends on temperature, being shorter at higher temperatures.

Annual cycle

There have not been any detailed observations of the annual cycle of this ladybird in New Zealand. Adults and larvae have been found with prey in late spring, and adults have been found with prey in summer. Like other ladybirds, the adults may overwinter and become active in the spring. There are likely to be several generations per year.

Walking and flying

Both adult and larval stages of Loew’s 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, aphids and probably other insects. The jaws are the primarily structures used for holding and chewing the prey. Legs do not appear to be used for holding food.

Adult Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312U]

Adult Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312N]

Adult Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312M]

Adult Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312Q]

Adult Loew's ladybird, Scymnus loewi, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 2CDE]

Side view of adult Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312T]

Three larvae of Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312R]

Side view of a larva of Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312V]

Adult Loew’s ladybirds can be recognized by their small size, covering with fine short hairs and black and brown colouration. The amount of brown is variable, but the head, front and lateral edges of the pronotum (first part of the middle body) are brown. Also the posterior (hind) lateral sides of the elytra (wing covers) are also brown. On some beetles, the brown on the elytra extends as far forward as the anterior (front) margin of the elytra, whereas on others it stops halfway. The adults are similar in size and appearance to the Dusky lady beetles, Nephus binaevatus, which are black with a pair of red spots towards the tip of the elytra. The adult mealybug ladybird, Cryptolaemus montrouzieri, are larger and quite different. The main part of the elytra is black, but the elytra tips, head and pronotum are brown.

The larvae of Loew’s ladybirds look like mealybugs being covered in white flocculent wax. They are very mobile and the head and legs can be seen on their underside. Larvae of Dusky lady beetles, Nephus binaevatus, are similar in appearance and size.

The larvae of the mealybug ladybird, Cryptolaemus montrouzieri are also coated in white wax. They grow larger and the underlying body colour is dark.

Adult Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312M]

Adult Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312N]

Larva of Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 312S]

Two larvae of Loew's ladybird, Scymnus loewii, (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 2CDF]

Adult Dusky lady beetle, Nephus binaevatus (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2LRM]

Adult Dusky lady beetle, Nephus binaevatus (Coleoptera: Coccinellidae) with what may be two eggs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2LS0]

Four larvae of Dusky lady beetles, Nephus binaevatus (Coleoptera: Coccinellidae) in a colony of New Zealand flax mealybug, Balanococcus diminutus (Hemiptera: Pseudococcidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2LS1]

Larva of Dusky lady beetle, Nephus binaevatus (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2LRL]

Underside of a larva of Dusky lady beetle, Nephus binaevatus (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2LS3]

Larva of Dusky lady beetle, Nephus binaevatus (Coleoptera: Coccinellidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2LRN]

Adult mealybug ladybird, Cryptolaemus montrouzieri (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 2863]

Top side of a fully grown larva of mealybug ladybird, Cryptolaemus montrouzieri (Coleoptera: Coccinellidae). © Plant & Food Research. [Image: 2CE4]

No natural enemies of the Loew’s ladybird are known in New Zealand. They are probably preyed upon by birds, spiders and predatory insects.

In New Zealand Loew’s ladybirds have been found feeding on mealybugs and aphids. The names of the aphid species have not been recorded. They may feed on other insects.

Adult female Long-tailed mealybug, Pseudococcus longispinus (Hemiptera: Pseudococcidae) on a leaf of Queensland kauri, Agathis robusta (Araucariaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 300D]

Part of a colony of Long-tailed mealybugs, Pseudococcus longispinus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 300A]

Part of a colony of Long-tailed mealybugs, Pseudococcus longispinus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3008]

Colony of Long-tailed mealybugs, Pseudococcus longispinus (Hemiptera: Pseudococcidae) on a leaf of New Zealand flax, Phormium tenax (Hemerocallidaceae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 300E]

Adult Loew’s ladybird, Scymnus loewii, (Coleoptera: Coccinellidae) on a leaf with aphids (Hemiptera). © Plant & Food Research. [Image: 312P]

Biological control of pests

Biological control of whitefly and other herbivorous pests can reduce the impact of the pests and the need to use insecticides. The Loew’s ladybird may contribute to the control of mealybugs in the home garden and commercial crops. If pesticides are needed to control other pests, it is advisable to use chemicals that will have minimal harmful effects on the ladybirds or to use them at a time when the ladybirds are not present.

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).

Charles JG 1989. Pseudococcidae, mealybugs (Homoptera). In: Cameron PJ, Hill RL, Bain J, Thomas WP ed. A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874 to 1987. Wallingford, Oxfordshire, UK, CAB International. Pp. 223-236.

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.