Wasps: Biological Control - Garden Critter of the Month

Wasps at a glance

Occupation:	Predator
Value to Gardener:	5/5 - Pest Controller and Pollinator
Danger to Humans:	4/5 – They can sting when provoked
Availability:	5/5 – They’ll arrive or you can buy some

Quick Intro

The wasp is likely an under appreciated garden helper. They are one of a few insects that duel as a predator and a pollinator. If left unthreatened they will be valuable additions to any garden.

Wasp morphology
WikipedianProlific, Wikipedia

Science Stuff

Wasps belong to the order Hymenoptera, which includes bees and ants. The main difference between a Hymenoptera (Bees, wasps and ants) and Diptera (Flies and mosquitoes) is the narrow waist for the Hymenoptera and small spoon-shaped halters are present in Diptera.

Wasps have biting mouthparts and an ovipositor (egg-laying organ). The ovipositor can be modified to sawing, boring, piercing or stinging. There are many different types of wasps, either specialising in a prey-item (spiders and caterpillars) or by biology (larvae deposited in plant leaves, creating galls or cuckoo wasps that lay their eggs in the nests of other Hymenoptera). Here is a quick list of a few major wasp families:

Ichneumonidae (For lack of common name, I’ll make it Drilling Wasps): These wasps have slender bodies and females have a long ovipositor modified to bore holes into plant stems to reach the larvae upon which they parasitise. Eggs are deposited into the larvae of moths, butterflies, flies, other Hymenoptera and lacewings.

Ichneumonidae
Dolichomitus imperator
Oviposition 

Gall wasps: These are wasps that deposit their eggs in plant material, causing localised swelling of the plant material and forms galls. These wasps are considered pests in agriculture. Families include; Eucharitidae and Pteromalidae.

Pompilidae (Spider-hunting wasps): These wasps vary in size, depending on the prey items size. They are often black with bright orange and red markings. Spiders are caught, returned to the nest where larvae are deposited in the paralysed spider.

Pompilidae
Spider-hunting wasps
Sphictostethus nitidus 

Vespidae (Paper wasps): These are the most common wasps and will be the main family discussed in this article. All species build papery multi-celled nests of chewed wood pulp and saliva. They are highly social and will defend their nests aggressively.

Vespula germanica
Vespidae
Paper wasp 

Eumenidae (Potter wasps): These are solitary wasps that excavate burrows or use mud to make nests. They deposit their eggs in the nest before introducing paralysed caterpillars.

Eumenidae
Potter wasp

Sphecidae (Mud daubers): This is a large family of solitary wasps. They also create burrows or mud nests. Adults feed on pollen and larvae are fed with insects. Females can sting, but are seldom aggressive. They can be used as biological control agents in agriculture, depending on their prey preferences.

Ammophila sabulosa
Sphecidae
Mud daubers 

One specific mud dauber that is regular visitors to my garden is the Flowerpot wasp, Pseudoplisus natalensis. I recognise them by their ‘white socks’. Females dig holes in the loose soil of the flower pots and bring leaf hopper (Ptyelus grossus) nymphs to the nest. They are fascinating to watch, they will fling out dirt from their burrow, leave and a few minutes later return with a paralysed leaf hopper to be store in the dungeon J. Which is great, because not only are the leaf hoppers a pest, but they have a nasty bite to them when they sit on you!

Habitat

Wasps, especially, paper wasps have diverse habitats and are found just about everywhere. Once a colony has been established, fertilised females can overwinter and new colonies are founded in spring, resulting in a continuous wasp presence.

Paper Wasp
Belonogaster dubia

They just have a habit of making nests at inconvenient locations, under door frames, in keyholes. Simply remove the nest at night (this prevents harm to both humans and wasps, but be careful – my mom is fearless when it comes to this J, she has forcefully relocated many colonies without a single sting J and no harm to the wasps either) and they will relocate to somewhere else, without losing your garden helper or being stung in the process.

Diet

Adult paper wasps feed on pollen and make great pollinators, since they are larger than bees and distribute more pollen to other flowers. Mine like the raspberry's flowers and since they’ve been pollinating it; the raspberry has given full fruits (all of the multiple flowers are pollinated and all set to fruit).

Adult paper wasps feed their young on chewed caterpillars. This season (summer 2012-2013) I have had a major caterpillar invasion of epic proportions! I have had about a 40% loss in tomatoes, all due to caterpillar feeding. The worst part is that they will not eat one whole tomato until it is completely consumed; they eat one or two holes in each tomato. This makes the tomato rot and fall from the plant. Others have gotten into some leafy vegetables as well, but luckily my trusty army of 1 persistent female wasp made off with all of them (in one day!) before too many vegetables were lost. (The caterpillar were mostly moth species, especially Chrysodeixis acuta, Silver U or Tomato semi-loopers, I’ll do a full pest profile on these soon J).

Paper Wasps Hunting
Belonogaster dubia

Silver U, Tomato semi-looper
Chrysodeixis acuta

Wasp SOS

Twisted-wing parasites: Is a highly specialised group of insects that resemble beetles. They belong to the order Strepsiptera and are parasites that live within other insects, mostly Hymenoptera and Hemiptera (True Bugs – stink bugs and the like). Stylopid females penetrate the host cuticle, they become sessile and remain in the body of the host and can be seen protruding from the abdomen. After insemination of females by flying males, stylopid larvae consume their mother (hemocelous viviparity). The larvae are mobile, they seek out and infect new hosts, where they moult into legless maggots that remain within the host, feeding of nutrients in the blood. Along with abdominal deformities, the parasites cause the host to become sterile and cause behavioural changes of the host. Infected wasps do not perform social colony tasks, instead they leave the colony and gather in clusters at suitable mating sites for the parasite. Female parasites of the Xenos vesparum species do not exhaust their host's reserves and may overwinter with their wasp host, whereas males exhaust their host’s reserves and the wasp dies at the end of the summer season.

Twisted-wing parasite
Strepsiptera, Halictophagida
Halvard, Wikipedia

Wasps – last thoughts

Even though they can be the stuff of nightmares, this season has made me realise how under appreciated they really are (even more than mantids J) and that can be excellent pollinators and great biological pest control.

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