INSECTS AROUND YOUR PROPERTY: FRIENDS AND FOES

Pam Pittaway PhD, Chrysalis Landscape Consultants

31 Douglas McInnes Drive, Laidley, Qld 4341

, on the net -

Some insect background:

Insects are animals without backbones, whose bodies are divided into three sections (head, thorax and abdomen), with six legs, with or without wings. They share may attributes with other classes of jointed leg animals in the phylum arthropoda (crustaceans, spiders, scorpions, millipedes, centipedes, mites and ticks).


An insect embryo showing the development from the ancestral arthropod type. It has legs (appendages) on every segment (A), to the modern insect (B). Modern insects have lost the legs on the abdomen, retain 6 legs on the thorax, and the legs on the head have become external mouthparts.

Diagram is from Figure 4.7, Entomology and Pest management 2nd Edition by L.A. Pedigo (1996 Prentice-Hall)

WHY ARE ARTHROPODS IMPORTANT?

By sheer numbers, insects are the most common organisms on earth. Estimates of 40 million insects for each acre of land have been speculated. Arthropods generally are important in food webs, and in nutrient recycling in the litter layer of all ecosystems. Without them important processes such as pollination, wood and organic matter decay would occur more slowly or not at all, and many bird, reptile, amphibian and mammalian species would starve.

On the down side, a single female insect can lay as many as 80 eggs per generation. If natural enemies are limiting, and if large expanses of uniform food plants or animal hosts are available, insects can build up to large numbers very quickly, doing a lot of damage by simply eating!

Maintaining a biologically diverse farm or garden, with abundant organic mulch and shelter trees and shrubs to harbour natural enemies such as spiders, other insect predators, birds, frogs and lizards will keep the survival rate of those 80 eggs per female to only one or two.

However if preferred plants (crops and ornamentals) are being attacked and if you want to target the pest species, you will need a ‘searching image’ of what the likely attacker is. This is vital if you wish to maintain good biological control on your property and not annihilate every insect by spraying chemicals.

HOW INSECTS ARE IDENTIFIED

Insects are classified into 24 winged orders, and 5 wingless orders. For example, order Lepidoptera is the moths and butterflies, order Coleoptera consists of the beetles, and flies are in the order Diptera. The characteristics of each order depend on the degree of change between immature and adult, the relative proportions and shape of the three body sections (head/thorax/abdomen), the presence/absence and type of wings, and type of mouthparts. For example all beetles have grubs as the immature phase, have a very broad connection between the thorax and the abdomen, have the first pair of wings modified as wing covers, and have chewing mouthparts. The immature stages of all bugs (Order Hemiptera) look more like the adult (nymph), have two pairs of wings, with a very broad connection between the head and thorax, and piercing and sucking mouthparts. Wasps, bees and ants (order Hymenoptera) have a maggot type of immature, with the adult having a very obvious constriction between the thorax and abdomen (‘wasp-waisted’), two pairs of wings, and mouthparts typically chewing and lapping. Members of the Hymenoptera are particularly important natural enemies as many of the females have an extension to their reproductive organs (ovipositor), enabling them to inject eggs into the eggs or larvae of other insects. By knowing the general characteristics of the different insect orders, it is possible to match the damage caused to a preferred plant, to a likely culprit!


Diagram of the chewing mouthparts of a grasshopper (Order Orthoptera) and a beetle (Order Coleoptera), and piercing-sucking mouthparts of a cicada (Order Hemiptera). Dotted line is where the head joins the thorax. Drawing is from figure 2.6 Entomology and Pest Management 2nd Edition by L.A. Pedigo (1996 Prentice-Hall).

MATCHING PLANT DAMAGE TO THE INSECT CULPRIT

Consider insect mouthparts to be like the attachments that can be added to a bobcat (skid-steel loader). The imprint in the soil, the type and size of cut, will match the type and size of the attachment. The same applies to insects and the damage they cause. If the insect is large enough, the use of a small hand lens or magnifying glass will prove what type of mouthparts it posses. However, be aware that grubs changing to beetles may also change what they feed on (Order Coleoptera), and caterpillars with chewing mouthparts change to butterflies or moths (Order Lepidoptera) with sponging mouthparts - most definitely changing what they feed on in the process! Therefore, to match the damage to the culprit, you do need to know the basic characteristics of the most common insect orders. The book A Field Guide to Insects in Australia by P. Zborowski and R. Storey (1995, Reed New Holland, Sydney) is very helpful.

Consider the tunneling damage to a leaf. The culprit must be small enough to be able to move inside the leaf, and must have chewing mouthparts to produce the tunnel. Hence, the culprit must be a larval form, either turning into a fly or a moth or butterfly (most beetle larvae are much larger). Large chunks missing from a leaf must come from a proportionally large insect, either an immature or an adult, with chewing mouthparts. The searching image could include adult or nymphal grasshoppers (Order Orthoptera), adult or larval beetles, or larval moths or butterflies.

Have you ever seen hypodermic spotting on leaves, sometimes associated with dimpling around the pinprick? This type of damage may not seem very serious at first glance (unless you’re selling flowers), but the culprit causing the damage can spread viruses and other specialist types of plant diseases via the ‘sharing of syringes’ between plants! The culprit in this case may be the very small thrips (Order Thysanoptera), or aphids or leafhoppers or whiteflies (Order Hemiptera). All bugs in the order Hemiptera have piercing-sucking mouthparts, which they carry pulled close to the underside of their body when in flight (see the cicada in the second figure).

RECOGNISING THE BENEFICIALS IN THE GARDEN (the friends):

(Here, I would suggest that you search the ‘Web’ (the world-wide not spiders’!!) for images and further information. Of course, there are also many publications available and “good-bug” suppliers will often provide illustrated catalogues.)

Of the 37 orders of insects and their arthropod cousins, only 9 have a majority of species capable of causing damage to plants. Yet even within these 9 predominantly pest orders, there are examples of beneficial species. For example, beetles (Order Coleoptera) include many potential pest species, but also include the beneficial ladybirds - and many flowers are pollinated by beetles. The potentially damaging bugs (Order Hemiptera) also include the predatory assassin bugs. Beneficial orders range from carnivores preying on other insects (23 orders), and scavengers or microbial feeders (21 orders). Of the carnivores, the wasps (Order Hymenoptera) are very important parasites of eggs and larvae, and preying mantids (Order Mantodea) and spiders are very important predators of nymphs and adult insects.

Even within the aphids, high numbers on some plants can be beneficial. To be able to insert their ‘hypodermics’ into plants to tap into the vascular system, aphids must match the biochemistry of the plant. Therefore, aphids commonly attack only a very narrow range of closely related plant species. Aphids are also very good food for the larvae of the beneficial ladybirds (the mini alligators to be found amongst a mass of aphids). Heavily attacked false cotton plants or milk thistles, can therefore help to build up the population of these desirable species.

Moreover, keep in mind that killing all caterpillars ensures that there will be no butterflies or moths! In a species rich organically managed property, soft-bodied insects such as caterpillars are important food sources for many native animals and birds. Many mud-nest building wasps also add at least one caterpillar per nest to feed their larvae before they emerge as winged adults. However, in the veggie patch where plant diversity is reduced to a few even-aged, mass planted food plants, the legacy of 80-odd eggs per female per mating can be devastating! Get to know the differences between the good, the bad and the down right ugly!!

Try comparing the Brown Bean Bug versus the adult Assassin Bug or the Black Bean Fly versus our Native Wasp.

SELECTING CONTROL METHODS THAT TARGET THE PESTS (the foes):

Physical Control Methods

Physical methods can be as simple as using your fingers to squash pest species, or by placing fine mesh over a preferred tree to exclude insects. Qld DPI has been trialing fine mesh screens to exclude fruitfly. The problem is, the mesh will also exclude beneficial insects responsible for pollinating flowers. Timing the application of the exclusion net is important, because fruit-fly maggots pupate in the soil!

Other physical methods immobilize insects on sticky surfaces, or in films of oil. Some wingless insects can be controlled by placing a protective, impermeable band around the base of a tree, and then adding petroleum jelly – or specialized sticky products such as ‘tangle trap’ to prevent access to the tree canopy. White oil assists in controlling small insects such as scale, mites and aphids, by coating their bodies with oil, immobilizing and suffocating them. White oil is a petroleum-based product, and can burn young leaves or soft foliage. Organic Crop Protectants are a company that specialize in organically certified products, and include a plant-based oil that is less likely to harm plants, in their product range (eco-oil).

Small insects such as whitefly and aphids can also be immobilised by hanging yellow or white strips of adhesive plastic in shade houses or the veggie patch. Insects attracted to yellow or white land on the surface and get stuck. Yellow or white containers filled with water and a few drops of washing-up detergent can also trap insects. The problem is that some beneficial species such as wasps are also attracted to the colour yellow.

Bio-Chemical Control Methods: (Here I exclude any reference to purely chemical insecticides)

Whilst excluding chemical insecticides from this over-view, I do include ALL methods that are neither physical nor predator based – they may be categorised as bio-chemical or simply bio-agents eg BT.

All animals share the same cell type, so any other animals in the garden are potentially at risk when typical chemical insecticides are used. However, there are strategic ways of using these chemicals, to reduce their non-target effects. Eco-Naturalure is a product developed by Oganic Crop Protectants that uses the very specific sex pheromone used by the Qld. fruit-fly to locate a mate. A microbial toxin is added to the bait, to kill any amorous fruit-flies that come in for the kill! Alternatively, the essential oil wild may can be used to attract male fruit-fly into a simple trap, leaving them to drown in the fluid!

Other strategies to reduce non-target damage are to use products that only become effective when the pesticide is eaten by the pest. One such product is the microbial pesticide marketed as Dipel or Thuricide (based on the bacterium Bacillus thuringiensis - BT). Only Lepidopteran caterpillars are affected (larvae of moths & butterflies). The product must be sprayed onto plants when the caterpillars are only small, to ensure they eat a sufficient quantity of it to kill them. Another product is Organic Crop Protectant’s Azamax, based on the plant extract Neem. Azamax has been formulated for applying to leaves, not for use in the soil.

Biological Control Methods

Biological control is the use of natural enemies to feed on all of those insect eggs and larvae, to keep the potential population explosions in check! The best generalist natural enemies are birds, spiders, preying mantids, lizards and wasps. Hover flies, lady birds (NOT the leaf-eating 28-spotted one), assassin bugs and lace-wings are other beneficial species that all should be welcomed by gardeners with open arms!! For commercial growers, companies such as Mundubbera’s Bugs for Bugs mass-rear specific natural enemies such as parasitic wasps and predatory mites, for sale. Mass-releasing such beneficials in commercial orchards or glass-houses is increasingly attractive for producers living the Clean Green image.

As with all growing systems there will be a wide range of strategies that may be used to control pests. The principle of INTEGRATED PEST MANAGEMENT is the corner stone of creating an environmentally sustainable pest control programme.

So, get to know the dynamics of the insects and arthropods in your garden, to enable you to recognise friend from foe!

A word of warning though – do not try to hold an Assassin-bug. You may regret it!

Useful web sites:

The Association of Beneficial Arthropod Producers

Australian Academy of Science

Search for yourself – save time – be specific with your key word – ie. Try “Brown Bean Bug”

Good Luck

Pam

Sheet updated10/20081 of 4