Cucumber: How To Grow - Fruit of the Month

Cucumber stats/requirements at a glance

Ease of Raising:	2/5       - Weekly check-up
Water:	4/5       - Daily
Sun:	5/5       - Full sun, no shade
Training:	2-4/5    – Moderate (on trellis)
Fertilise/Feeding:	3/5       – Moderate (monthly)
Time to Harvest:	3/5       – Moderate (2-3 months from seed)
Frost Hardiness:	1/4       – Very Tender (cannot take light frost)
Uses	Culinary, Pollinator attractor
Most Problematic Nemesis:	Powdery Mildew
Container Plant:	Can be, but preferably train up a trellis

Poisonous cucumber
Cucumis trigonus

Quick intro

Cucumbers are not a particularly important food crop, but they do bring some interest to food dishes and provide refreshing taste to summer salads. Cucumbers can be eaten raw and sliced into salads, pureed into soups or chopped and cooked into Indian-style vegetable dishes. Additionally, young parts of the plant (leaves, shoots, seeds and roots) are also consumed as food. Cucumber do very well in hot climates, with plenty of water for fruit set, and new cultivars are highly productive and only require one or two plants to provide enough for a family.

History

The present day cucumber is thought to have its origins on the foothills of the Himalayas from the wild Cucumis hardwickii. The plant has been cultivated in India for 3000 years, from Cucumis hystrix, and was introduced to ancient Egypt, Greece and Rome. Several varieties of cucumbers can be found worldwide today with three main varieties; slicing, pickling and burpless cucumbers.

Science Stuff

Cucumbers (including gherkins and melons) belong to the same family as the squash and pumpkins, the Cucurbitaceae, but cucumbers belong to a different genus, namely Cucumis. The most widely cultivated species of cucumber is Cucumis sativus. Several wild cucumbers are also available, but are not commercially grown, specifically the native African cucumbers. Here is a quick run-down of each;

Cucumis sativus – three main varieties. Slicing cucumbers are eaten raw and unripe (green). These are mainly used in salads and cooked dishes. Pickling cucumbers are pickled for flavour and are shorter and thicker than slicing cucumbers. Burpless cucumbers are sweet, nearly seedless and have a thinner skin. This makes them more popular for raw consumption, but need to be grown in a greenhouse to prevent pollination by insects.

Cucumbers, slicing, pickling and burpless
Cucumis sativus
Muu-karhu, Gruepig, Ariya shookh
Wikipedia

Cucumis metuliferus – the African horned cucumber. This is a round variety with large spines. It is eaten when fully ripe (bright yellow-orange) and is supposed to have notes of banana, melon and citrus – but I highly disagree (see later for more details J).

African horned cucumber
Cucumis metuliferus
Forest & Kin Starr
Wikipedia

Cucumis hirsutus & Cucumis quintanilhae - two African varieties, but largely undescribed.

Cucumis hemifructus – another African species, known as the ‘Aardvark cucumber’. It is also known as the Kiwano, melano, African horned melon, horny cucumber, hedged gourd or English tomato (who knows what’s on with the last name). This is a round variety with large spines. The fruits can be eaten young, mature green or when fully ripe (bright yellow-orange). It is used mainly in desserts and is supposed to have notes of banana, melon and citrus – but I highly disagree (see later for more details J). It originated in Africa, the Kalahari desert. It was introduced to Australia, where it became a weed, and is now cultivated in California and New Zealand.

Aardvark mother & baby
Orycteropus afer
Scotto Bear
Wikipedia

Cucumis melo – that’s the melon. Not fond of melons, but I imagine the growth requirements are largely the same as cucumbers.

Melon
Cucumis melo
Seth Vidal
Wikipedia

Cucumis anguria – the burr gherkin. A West African species that cannot be interbred with the commercial gherkin, but it can be eaten and pickled.

Burr gherkin
Cucumis anguria
Eugenio Hansen
Wikipedia

Cucumis myriocarpus – the paddy melon, a mostly inedible species from Spain.

Paddy melon
Cucumis  myriocarpus
Golden-elm
Wikipedia

Cucumis zeyheri – an African species, very bitter and inedible. Also known as the wild cucumber or bitterappel (again Afrikaans for “bitter apple”).

As you can see, most of the other cucumber species are bitter and inedible. This is due to a compound found in cucumbers, known as cucurbitacins. The cucurbitacins are cytotoxic (causes death to cells) and are often poisonous to livestock, we (humans) perceive this as a bitter taste. Cucurbitacins are species related, where Cucurbitacin C is found in Cucumis sativus, and Cucurbitacin A in other species of Cucumis. 

The burpless cucumbers are parthenocarpic, meaning that they can produce fruits without pollination/fertilisation. This prevents the production of Cucurbitacins that results in bitter tasting fruits and hence they are grown in greenhouses to prevent pollination. The varieties of slicing cucumber that I have (and the African horned cucumbers) do not produce fruits without pollination. Thus I will be discussing cucumber pollination hereafter.

Growing Cucumbers

Cucumbers are grown outdoors in regions with warm climates.  In temperate or colder regions, cucumbers are grown indoors under glass- or greenhouses (and thus it would be better to get the burpless varieties, since pollinators are not available).

Cucumber plant
Cucumis sativus

Cucumber seeds are sown directly into the ground, or can be started indoors and moved out to the garden once the plant has 3-4 leaves and the threat of frost is over. Seeds should be sown in soil that has reached at least 16^oC (60^oF), this means well into spring or started indoors under a cloche (this can be an overturned transparent plastic bowl or bottle).

There are two main ways to grow cucumbers:

1 cucumber) Over the soil. This is where the cucumber vine is left to trail over the ground. Problem with this is that fruits either rot on the wet ground or they become hard and yellow on the side that is in contact with the ground. This can be prevented by placing straw or plastic underneath developing fruit.

2 cucumber) Trellis. Many different trellises have been fashioned for cucumbers both in pots and directly in the garden. I have my trellis propped diagonally against the wall with enough space between the wall and the trellis for the cucumber vine to grow and bear fruits. This negates the soil contact issue and also saves soil space for some other vegetables!

The cucumbers will start to produce 1-2 months after sowing. Many standard cultivars are very prolific and two plants produce about 6 cucumbers (a good 30-25cm) every two weeks. You can also stagger the crop, by planting the second set cucumber(s) one month after the first or after the first set has started to flower.

I do not limit the amount of cucumbers on a plant, since they have such a quick turnaround time for fruit set and increased soil fertilisation (every two weeks) during fruiting should help it along. Pinch out the growing tip (with your fingernails or cutters), two leaves after the first fruit – this will encourage a more bushy nature with more fruiting side-shoots.

The first flowers produced are males, after which female flowers emerge (small cucumber behind the flower). If you have a lack of pollination (our bees only have eyes for the basil flowers! L) – then the flowers need to be pollinated by hand. The female flowers are easily pollinated by using a soft paint brush, scoop out some pollen (yellow dust) from the male anthers and deposit on the female stigma. The male anthers have a single yellow structure, whereas the female sigma is a light yellow three-lobed structure, see Squash for more details on hand pollination. For burpless varieties, remove the males, since the females develop fruit without pollination.

Cucumber flower
The one on the left is not pollinated and died.
Cucumis sativus

The fruits will hang from the trellis as they swell, you can support them with thick twine tied around the stems several times- this prevents stem breakage.

Cucumber fruit
Cucumis sativus

Other Cucumber Tips

Cucumbers, as with squash and pumpkins, are susceptible to powdery mildew. Efforts are being made to breed more resistant varieties. Prevention of powdery mildew is to keep the leaves dry, so water at plant stems, and you can also spray some of my organic control as prevention.

Powdery Mildew

Harvesting & Storing

Cucumbers can be harvested when small (10cm) or fully swollen (30cm). Some cucumbers have spines, but these are easily removed by scraping with a butter knife. Cucumbers do not keep well after harvest. The shelf life can be extended by refrigeration (in a plastic bag with a few drops of water to prevent shrivelling), will keep for about a week.

Seed Collection & Storage

Cucumber seeds are harvested from botanically ripe fruits. This is the same for squash. Botanically ripe cucumbers are yellow and mushy, bitter and inedible! The seeds are extracted and the pulp washed from the seeds. You can also ferment the seeds, but all I manage to get is germination and not fermentation – so pick mushy fruits that have already done that for you J. The seeds can be stored in labelled glass jars for up to 5 years.

My Cucumbers

I have the Starke Ayers Ashley variety – produces thick, up to 30cm cucumbers and is very prolific. Some spines are present.

African horned cucumber – I decided to try this. The plants grow very well –trailing all over the place, but they are slow to produce fruits. The fruits are horrible – very bitter – I was not impressed especially after being lied to about how nice they are! They do have a large ornamental value, for those interested in some strange looking plants, but as an edible crop - no.

African Horned Cucumber
Cucumis metuliferus

Bitterappel – We have a bushveld next to our house on the same property. We find all kinds of interesting things in there. This year, for the first time that I noticed, we came across some wild cucumbers. I first had them wrongly identified as there is loads of confusion on the internet about the African cucumbers. So I thought I till give it a try (this was before sampling the African horned cucumber) and it is so horrible that the bitterness will even stick to water K!!! K Eish! After that unpleasant experience, I had tons of suspicion about the African one – so did not have such a humongous bite of that! The other problem is that they smell so wonderful, much like a banana melon, but Egh! So, I think it is safe to say that these wild cucumbers are likely Cucumis zeyheri and that I won’t be planting any African cucumbers again.

Wild cucumber
Cucumis sp.
(likely Cucumis zeyheri, Bitterappel)

On that note, I think it was a bunch of people who have the genetic defect for tasting bitterness that wrote the descriptions! Yes, about 70% of the population can taste bitterness, whereas the other 30% have a mutation in the gene and they cannot taste bitterness – and will likely have more appreciation for ‘other’ flavours of bitter cucumbers! J Apparently there are non-bitter cultivars … so maybe I got cheated instead!

Last note, I had some lemon cucumber seeds, but got confused about whether I planted them or not. Thought that some of the African ones were lemons until they started fruiting – oh the horror! J Anyways – will try the lemons again next season and report back.

So stick to Cucumis savitus!


- Update 13 Nov 2013 - 

I have finally gotten some lemon cucumbers growing!!! BUT they aren't all good to eat, some of them are bitter! Not as much as the African ones, but there are one or two that come out bitter. Besides I don't taste the difference between them and normal cucumbers (maybe a bit sweeter?) - so I decided to stick to my Ashley! J

Lemon Cucumber
Cucumis sativus

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Please share with fellow gardening enthusiasts via the various sharing buttons at the end of posts/pages! Else you can vote for posts through the Google reactions bar at the end of articles. To stay up to date I have provided several reader and social networking platforms with which to subscribe: Twitter, Pinterest, RSS Feed Reader or Email/Follow directly using the Blog Followers widget on the left hand side toolbar. Thank you for reading and please feel free to ask if questions arise - I appreciate comments and ideas too! 😆

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DIY Bird Deterrent (Part 1)

During the summer growing season we have had some problems with Black-eyed Bulbuls that help themselves to our tomatoes, raspberries and figs. The nasty little buggers always managed to get to the fruits just when they’ve ripened – the cats aren't doing their jobs of scaring the birds away J!

 

Black-Eyed Bulbul - what naughty little birds!
Pycnonotus tricolor
Snowmanradio, Derek Keats
Wikipedia

So with some old CDs and a bit of creative savvy I made a few bird deterrents. Initially I wanted to purchase one of those reflective bird pyramids, but after seeing the price and surviving a minor heart attack – I decided to create my own based on the same principle.

So birds' visual colour - and light spectrums are different to humans. Humans can see in the 400-750nm wavelength range (the visual light range, indicated on the figure below). Our range has a normalised bell curve (the purple curve on the left side of the figure below) and our optimum colour range peaks at 555nm (which is green). Whereas birds have three optimum range peaks, one at green (508m), blue (445nm) and red (565nm). This makes birds more sensitive to these colours, red being the most prominent. By incorporating red and reflective surfaces into your bird deterrent devices will make your garden a literal eye-sore to birds and they will avoid landing close by.

Bird vision: as compared to human vision.

Top: Electromagnetic spectrum of light (note circle indicates the visible light spectrum); Inductive load & N174, Wikipedia.

Left: Human visual spectrum, with normalised curve superimposed, same axes lables as on right; Vanessaezekowits& BenRG, Wikipedia. 

Right: Bird visual spectrum, L. Shaymal, Wikipedia.

So I took some old scratched up CDs, glued some red and mirror mosaic pieces onto them and voila! It works really well… given the sun is shining J. A lot less expensive than the bird pyramids! Hung one close by the chicken coop to scare off would-be pigeon scavengers that eat all the chicken pellets – don’t worry; it is hung at pigeon-eye level, not chicken eye-level, so the chickens are unaffected J. The CDs swing around when the wind blows, which scatters light across the garden and helps to fend off fruit thieves.

DIY Bird deterrents, front (left) and back (right) hung from tomato stakes. Now the tomatoes and chicken pellets can be spared!

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Please share with fellow gardening enthusiasts via the various sharing buttons at the end of posts/pages! Else you can vote for posts through the Google reactions bar at the end of articles. To stay up to date I have provided several reader and social networking platforms with which to subscribe: Twitter, Pinterest, RSS Feed Reader or Email/Follow directly using the Blog Followers widget on the left hand side toolbar. Thank you for reading and please feel free to ask if questions arise - I appreciate comments and ideas too! 😆

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Leafhoppers - Garden Pest of the Month

Leafhoppers at a glance

Type of Damage	Pierce-sucking
Plant Symptoms	Browning & curling of leaf edges
Favourite Plant	Tomatoes & Potatoes
Control	Biological (predators: spiders & mantids)

Quick Intro

These jumping insects are common in the garden, especially around the Acacia trees in our garden. Not only do they attack plants, but they lower the plants’ condition that allows secondary attack by other pests and diseases. They are easy to spot on plants, but be careful as they can bite you too!

Science Stuff

Leafhoppers belong to the insect Order of Homoptera, which means that their wings are completely membranous (unlike Hemiptera insects where half of the wing is sclerotized or hardened. They are a major plant-feeding group causing direct damage to plants as well as spreading plant pathogens (disease). They produce ‘honeydew’, a sugary excretion which ants collect as food.

Leafhoppers belong to the Cicadellidae family (cousins of the cicadas J) and contain many species, often brightly coloured. Their wings are held roof-like over the body and their hind legs have a single row of spines. They are excellent jumpers, which make them hard to catch, so leaf it to the ambush predators J.

Habitat & Feeding

They are highly host specific, meaning that they feed exclusively on one host and will adapt accordingly. A white patch occurs on plant leaves after feeding, due to the destruction of chlorophyll (green pigment) in that area. In high numbers the leaves start to brown and curl back onto themselves. A characteristic v-shaped browning of the leaf tips is a symptom known as ‘hopperburn’. In South Africa we have 350 known species and 20 000 species worldwide.

Hopperburn on tomato

Diseases

Leafhoppers transmit viral diseases (maize streak virus), fungal and bacterial diseases.

Potato Leafhopper (PLH)

I will be focusing on one specific leafhopper common in vegetable gardens or agricultural lands. (It was quite the mission to identify the leafhoppers in my garden, as my trusty insect book let me down and only had 7 species. So this meant going through zillions of pictures on Google to find one with a scientific or common name.)

There are several species of potato leafhoppers, but the one in my garden is Empoasca fabae. It feeds on many cultivated crops including eggplants, strawberries, potatoes and tomatoes. They prefer to attack my potatoes and tomatoes (likely due to both plants belonging to the same family, Solanaceae). They are bright lime green with white eyes – apparently there are six white dots on the back of the head that can be seen with magnification, as if I can get close enough for that before they jump! J Their nymphs look similar, but are smaller with no wings.

Potato LeafHopper Adult
Empoasca fabae

They arrive during spring time and can have several generations per season. Depending on your local climate, the adults either overwinter or migrate to warmer areas.

Potato leafhopper nymph
Empoasca fabae

I have another leafhopper species in my garden, but I can’t identify it, I find many similar looking species, but not this exact one. I have noticed that these are larger than the PLH and their bite is more painful! J

Leafhopper
Unidentified species

 Control

Leafhoppers are tricky to control. Physical removal of infected plants can be effective, but seeing as they will simply jump off or migrate into the garden, physical control is likely only effective short term.

Chemical control: Is the most effective. But the problem with chemical control (even home remedies) is that these insects are too ‘high’ up the evolutionary complexity scale and their pesticides will likely harm other higher insects as well. There are some insecticidal soaps available.

Biological control: This will be the mantids and spiders, wasps prefer caterpillars. I had a huge lack of mantids this season as none of last seasons’ females laid eggs in my garden (should likely go do some hunting for egg cases next season J). So I had a bit more of a problem with leafhoppers this season, but the spiders and wasps managed to move into the gap left by the mantids and kept most of them under control. (Also had more stink bugs in the garden as well, mantids also ate those last year, check my Mantid post.)

Preventative tips

Healthy plants should be able to resist most of the damage caused by leafhoppers and should produce well.

Apparently you should avoid over-fertilisation of your plants as this will increase the leafhopper populations in your garden.

They lay their eggs on plant stems. Each female can lay 2-3 every day for up to 50 days. These eggs hatch in 7-10 days. So the removal of spent or dead plants will likely decrease the amount of suitable egg laying places. That includes regular weeding! J

If you are close to alfalfa fields you may have more problems with PLH, especially when the alfalfa is harvested and the insects need a new food source.

Something cool

A sister family, Membracidae, the Treehoppers have a fascinating evolutionary phenomenon. They have a large pronotum, a part of the prothorax, known as a helmet. The helmet usually resembles thorns and aid camouflage. But, some species have developed very ornate helmets. Some scientists speculate that these resemble aggressive ants or animal droppings.

Learhopper morphology
Original picture: Eupteryx aurata, Sarefo, Wikipedia

Prud’homme and colleagues (2011), investigated the strange helmets of the treehoppers. They found that the helmets are actually appendages that resemble a modified wing. There is a set of genes (known as a gene family), the Hox gene family, present in all animals and is responsible for the correct development of limbs/wings during the formation of the embryo. The helmets of the treehoppers were speculated to have ‘escaped’ the constraints of the Hox gene and where able to develop into diverse appendages. This was due to the fact that, wings have a restricted shape due to their function in flight, whereas the appendages can take on a number of different shapes to facilitate camouflage. In the 250 million years of insect evolution, this is a rare and unusual case – but if there is one thing that biology and especially genetics has thought me , is that just about anything is possible, since nature does not abide by the supposed rules that humans have J. So I just thought I would share this interesting evolutionary bit with you – I hope I didn’t over-science it J.

Reference:Prud’homme B. et. al. (2011) Bodyplan innovation in treehoppers through the evolution of an extra wing-like appendage. Nature: 473 83-86.

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Please share with fellow gardening enthusiasts via the various sharing buttons at the end of posts/pages! Else you can vote for posts through the Google reactions bar at the end of articles. To stay up to date I have provided several reader and social networking platforms with which to subscribe: Twitter, Pinterest, RSS Feed Reader or Email/Follow directly using the Blog Followers widget on the left hand side toolbar. Thank you for reading and please feel free to ask if questions arise - I appreciate comments and ideas too! 😆

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Sweet Potato: How To Grow - Vegetable of the Month

Sweet Potato stats/requirements at a glance

Ease of Raising:	5/5 - Very easy
Water:	2-4/5 – Twice a week to daily
Sun:	4/5 - Full sun, will tolerate shade
Training:	1/5 – None, except for unwanted runners
Fertilise/Feeding:	3/5 – Moderate (monthly)
Time to Harvest:	4/5 – Moderate (3-4 months as leaves die, but well worth the wait)
Frost Hardiness:	4/4 – Very tender (can’t take light frost)
Uses	Culinary
Most Problematic Nemesis:	Nothing too serious
Container Plant:	No – produces tubers away from main base

Ipomoea purga
Köhler's Medizinal-Pflanzen in naturgetreuen
Abbildungen mit kurz erläuterndem Texte
1887)
Kurt Stubers Online Library

Quick intro

There isn’t much mention of sweet potatoes in most gardening books, yet it is extremely easy to grow and the harvest is bountiful. These tubers can be eaten baked, boiled or candied – even alcohol can be made from sweet potatoes. Young shoots and leaves are sometimes eaten as greens or given to livestock. Given enough space, sweet potatoes grow vigorously and produce a lot of tubers, but they may take over the garden if not kept in check!

History

It is generally assumed that the sweet potato has its origins in tropical America, specifically from wild Mexican Ipomoea trifida. It may have been cultivated since 8000BC in Mexico, Central and South America, and the West Indies. Columbus returned from his first voyage to the New World to Spain with the sweet potato. Thereafter the Spaniards and Portuguese transported it to Asia and Africa, and by some way it was transported to Polynesia and New Zealand as well. Lately, it is an important root crop in Asia and Africa, but is also cultivated in the Americas and Europe.

Science Stuff

The Sweet Potato, Ipomoea batatas, belongs to the Convolvulaceae (the morning glory family) and is often confused with yams (Dioscorea spp.) and is not a true potato (Solanum tuberosum). There are ornamental varieties, which are called tuberous morning glories, which to my mind it a better definition for the root crop.

The Golden Morning Glory
Aniseia aurea

There are different varieties of sweet potato, elongated to globular, white, tan, yellow, red, purple skinned and ones with white, yellow or orange flesh.

Ipomoea trifida, and some other wild sweet potato varieties are still bred into the domesticated lineage, as these varieties have high genetic diversity and their tubers contain more starch.

Growing Sweet Potatoes

So the one big thing I read on sweet potatoes is that it does not tolerate frost, considering that it is a subtropical to tropical crop. Therefore it should be grown in regions with five months (or more) worth of growing season. Cold tolerant cultivars have been introduced to the UK, but it still requires the protection and added heat from tunnels, frames or green houses to crop reliably.

Sweet Potato Flower
Ipomoea batatas

It prefers temperature above 24^oC (75^oF), but will tolerate temperature as low as 15^oC. It likes lots of sun and warm nights. Apparently it likes a lot of water and is sensitive to drought, although mine did not have the slightest problem with this – the tomatoes are more thirsty that the sweet potato! Water-logging may cause the tubers to rot, but there is no such threat in SA J

It will appreciate some compost and produce larger crops, but it can cope with poor soils and many farming conditions. The sweet potato requires little weeding, as it is a weed itself, excluding all other weeds (although mine was able to co-habituate with some miss-placed potato plants). Make sure that the soil is loosened up to 25cm for tubers to form properly.

Other sweet potato tips

Make sure to keep an eye on its trailing nature as it will creep into everything and needs to be restricted if grown amongst other vegetables, else you can plop it somewhere in the garden and let it carry on.

Sweet Potato Plant
Ipomoea batatas

The plant does not have problematic pests or diseases, I had a few caterpillars feeding on its foliage, but luckily my wasp army made off with the invasion soon enough J.

Harvesting and Storing

Sweet potatoes are harvested once the leaves start to yellow, usually 4-5 months after planting. Leaving the tubers in the soil after the plant has died ensures that the starch content increases and the tubers become sweeter, but the tubers must be harvested before the first frost.

Sweet Potato Tubers (White)
Ipomoea batatas

Sweet potatoes need proper curing to become sweet and moist. This can be done by storing them in a warm (26^oC, 80^oF) and humid room with good ventilation for 5-10 days. Afterwards the sweet potatoes can be stored at 12-15^oC (55-60^oF). To low temperature causes root to harden, whereas to high and dry conditions cause roots to shrivel. So I suggest storing them in a paper bag to level out the conditions a bit more. Properly cured sweet potatoes can keep for up to 12 months, just check them regularly for any signs of disease or rot.

Propagation

Sweet potatoes do best when grown vegetatively- that being cuttings or ‘slips’. Cuttings of sweet potato vine root easily and rapidly in water. Slips are similar to potato ‘eyes’; half of the tuber can be placed into a cup of water and left in the water until the tuber produces shoots, after which it can be planted into the garden.

I suppose you can get sweet potato plants/cuttings and a nursery, but no such luck here. I let some store-bought sweet potatoes produce slips and planted them in the garden.

As with the potatoes, keep some smaller tubers to produce slips in the next season.

My Sweet Potatoes

So, again, as with the potato – I don’t have a ‘formal’ sweet potato cultivar. I have made slips from white and orange flesh varieties. You will notice that some of your sweet potatoes will grow slower than the others (and they’ll have leaves that curl inwards), these are poor stock and their smaller tubers should rather not be kept as slips for the next season.

Sweet Potato Vine
Ipomoea batatas

A morning glory with identity crisis!

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Please share with fellow gardening enthusiasts via the various sharing buttons at the end of posts/pages! Else you can vote for posts through the Google reactions bar at the end of articles. To stay up to date I have provided several reader and social networking platforms with which to subscribe: Twitter, Pinterest, RSS Feed Reader or Email/Follow directly using the Blog Followers widget on the left hand side toolbar. Thank you for reading and please feel free to ask if questions arise - I appreciate comments and ideas too! 😆

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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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