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She might look cute, but the ladybird is one of the insect world’s best killers.

And today, staff at the Royal Botanic Gardens Melbourne Nursery will let the killer ladybird loose in a battle against mealybugs and other minibeasts.

"We’ve been using ladybirds and other good bugs, like green lacewings, as an alternative to chemical sprays for some time now," said David Robbins, Nursery Coordinator.

Mealybugs are a serious pest. They feed by sucking sap. They are difficult to control with pesticides, largely due to their waxy covering and their habit of infesting sheltered plant parts which makes it difficult to spray effectively.

"The Nursery contains some of the Gardens’ most prized specimens, including rare and threatened species, and it is crucial that we protect these in the best way possible. Ladybirds and green lacewings provide the perfect solution," he added.

The Royal Botanic Gardens Melbourne receives the ladybirds from a private company. Once released, they rapidly disperse through the nursery, laying eggs in any mealybug-infested areas they find.

Nursery staff will be joined by students from Narre Warren South P-12 College in their battle against bad bugs.

The mealybug ladybird

Cryptolaemus montroutizieri.

Ladybirds are used by the Royal Botanic Gardens Melbourne as an alternative to chemical sprays to help reduce insect pests.

The ladybird lays up to ten eggs a day directly into the egg masses of common pest insects such as mealybugs. These yellow or orange eggs can be found attached to the underside of leaves, often near the aphids, which will become the baby ladybird’s first snack. One ladybird larva can eat up to 350 aphids during the three weeks it takes to become a pupa.

The ladybird larvae are bizarre looking earwig-like creatures, which are sometimes mistaken for pests themselves. The larva pupates for about 7-10 days, after which the adult appears.

The adult ladybird is about 4 mm long, oval in shape with an orange head and black wing covers. As adults, ladybirds also feed on both eggs and larvae of these pests.

• Such was the voracious appetite of C. montroutiziera, that it and another species of ladybird, Rodolia cardinalis were introduced into California in 1905. The hope was that they would control cottony cushion scale, a common citrus pest.
• Ladybirds were also introduced to Auckland, New Zealand in 1897 and again in the 1920s, and they have since spread successfully to other areas.

They are also exported to Europe to control insects that prey on vegetables grown in glasshouses.