10 best beneficial insects in NZ gardens

http://nzgardener.co.nz/10-best-beneficial-insects/

1. Steel-blue ladybird larvae
Yes, I know: everybody loves ladybirds. These beetles eradicate aphids on your prized roses and other ornamentals. But they don’t eat as much as you might think. It’s actually their larvae that consume a fair amount of prey when they are in full growth cycle. Think teenagers, fridges, pantries and hollow legs. Although a few ladybird species scoff aphids as their preferred food source, others will grab anything that walks by: psyllids, caterpillars, mites and whitefly. So when it comes to lowering specific pest populations, only those ladybirds that confine themselves to one or two types of prey are reasonably useful. A good example is the steel-blue ladybird (Halmus chalybeus). It feeds on scale insects and loves to cruise the very places where its prey is common: up your citrus trees and on your flax, hydrangeas and rose bushes.

2. Mealybug-munching ladybirds
The so-called mealybug ladybird has a tongue-twister of a scientific name: Cryptolaemus montrouzieri. I think it’s beautiful – it sounds like a song. Anybody with an issue with mealybugs knows how difficult it is to control these woolly sap suckers. Mineral oil sprays need to be applied regularly and even the harshest systemic insecticides are often not enough to eliminate them. Thank goodness, then, for the mealybug ladybird. Its larvae are always on the hunt for a mouthful of cotton wool. Ironically, these ladybird larvae also just happen to look like overgrown mealybugs: yep… a wolf in sheep’s clothing.

3. Harvestmen
I’d like to take a look at the creatures we often call daddy long-legs. Our silly use of vernacular names has led to a confusing situation in which all sorts of unrelated invertebrates are given that label simply because they have one thing in common: long, fragile legs. The harvestman has eight of them and a body that consists of just one discernible segment. This predator, somewhat related to a spider, tends to run around the ground and the lower parts of plants. Anything of suitable size can be prey, from its own siblings to small slugs. Although it is a very general predator – making it a relatively useless predator for specific pest species – it has the ability to survive in unsprayed gardens when there aren’t many pests about. That means that harvestmen are often the first ones on the job when pests wake up and start to multiply in spring. There are 12 species of harvestmen, but Phalangium opilio is the one that appears to be most partial to the eggs of the cabbage white butterfly.

4. Spiders
Ah – arachnids! People often hate them, but I reckon they’re brilliant, especially as they all have clever strategies to capture their prey. Some jump on their quarry; others run them down. Web builders employ the ambush trick, while others encourage moths to visit their web sites by releasing a chemical that smells like irresistible pheromones (sex scents) from a female moth. The poor male moths think they are going in for the kill and end up being the kill instead. There’s a wonderful statistic from the UK that says that all the spiders over there collectively capture and eat an equivalent quantity of insect meat, every year, to the total weight of the human population in that country. They may make you shudder, but please look after your spiders; we need them more than they need us.

5. Predatory mites
These are useful little tyrants to have in any garden. The largest species, and the easiest to spot with an un-aided eye, is the bright crimson whirlygig mite (Anystis baccarum). It runs around like an idiot in a ploy to cover as much ground – or leaf – as possible, to increase the chance of encountering its prey. I’ve seen them carrying away caterpillars four times their own size! Another much smaller, dull-red predator mite can often be found wandering among colonies of spider mites. Just look at your beans, pipfruit, stone fruit or box hedges. This predator (Phytoseiulus persimilis) quietly goes about its business, eating spider mites and their eggs. Phytoseiulus persimilis is so good at its job that it is bred in captivity (by BioForce and Zonda) to help commercial growers keep spider mite infestations down in their crops. It’s a mighty, domesticated control agent.

6. Hoverflies
Hoverflies – those smallish flies that hover dead-still in front of flowers all over your garden – have very clever maggots. Some of our native species lay their eggs amongst aphid colonies and they do that for a good reason: their maggots are carnivores and wreak havoc and carnage in the aphid population.

7. Ground beetles
Stealth and speed, determination and voracious predatory behaviour are some of the traits associated with these black beetles, commonly found in your garden’s litter and mulch layers. Their official scientific family name is Carabidae (carabid beetles) and I suppose they’re in the shape of the archetypal beetle. You can’t miss them. These beetles have sharp mandibles (even as immatures or grubs) that can pick up and hold any type of prey that fits the right dimensions. Their job is to “keep the balance” down in the soil. But some species have a wonderful preference for slugs… and that, surely, is music to many a gardener’s ears!

8. Parasitic flies
Believe it or not, there are parasitic flies buzzing about in your garden. Trigonospila brevifacies is a small (half the size of a common housefly) but beautiful fly that  as introduced to New Zealand from Australia in the 1960s to help control nuisance leafroller caterpillars in orchards. The female fly lays a single egg just behind the leafroller caterpillar’s head. The maggot that hatches immediately burrows into the caterpillar’s body and starts eating its innards. How cool is that? Just like in the film The Mummy, the maggot completes its lifecycle inside its host, before a new parasitic fly emerges through the wasted body.

9. Parasitic wasps
Some parasitoids are host specific and are therefore really good at controlling pests. Two species are very much in demand by commercial growers – Encarsia formosa and Aphidius colemani – and both are commercially available. Encarsia formosa is perhaps the most famous parasitic wasp in the world. It has long been used to control whitefly on greenhouse tomatoes. Aphidius colemani is a small parasitic wasp that lays its eggs inside aphids. To attract these parasitoids, plant wildflowers, especially umbelliferous species such as wild carrot, parsley and Queen Anne’s lace. They provide a smorgasbord of pollen and nectar.

10. Ichneumon wasps
These larger parasitoids are quite visible and elegant to watch as they search your plants for smells and trails of caterpillars and other potential hosts. Their antennae move constantly, sometimes “drumming” on leaves and twigs to pick up chemical cues. Some ichneumonids parasitise caterpillars; others go for the pupae or chrysalids. A particularly beautiful black and white species with orange and black legs, known as Xanthocryptus novozealandicus, sniffs out lemon tree borer grubs inside the twigs, depositing an egg inside the host’s body. Instead of a borer beetle, another ichneumonid wasp will hatch from the internally consumed body.

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