Roots 'n' Shoots: April 2013

Saturday, 27 April 2013

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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Friday, 26 April 2013

Updates

Hey hey

Just a quick pop-in to let you know that I have done major updates to all posts and the blog in general.

Pages:

I have removed the pages which do not get lots of hits and replaced them with more useful ones, such as the
Index & Info page, which tells you whats happening around the blog and provides more convenient links to article series (using the Archive tab on the right is very tedious).

I moved the titles around under Edibles to make for easier reading.

I have added Garden Guidelines, which I will update with new tips applicable to all types of fruits and vegetables.

Under Pest Control I have added a recipe for the control of red spider mites! This page is constantly being updated, so remember to pop in!

Soil page has had a major re-vamp - I updated the titles for easier reading and redid all the pictures to high quality textures. This is a popular reference page it seems for the pictures and it appears that the new pictures are greatly appreciated J

Lastly the Reference page is also updated with books that I purchase and a quick review of each.

Posts:

I have updated the Potato post with mention of red potato cultivars that are less palatable to those irritating maize beetles.
The Sweet Pepper post has been updated to include the small cultivar, which copes better with the African sun.

Also for all my posts I have added some vintage botanical illustrations. I got most these from Vintage Printable - beetroot, oregano and eggplant from Kurt Stubers Online Library (see tabs on the right for links to other free resources). They are really lovely, especially the Squash and Tomato prints - for any of you who appreciate botanical prints like me J

I have added morphology pictures to the garden critter posts: Praying Mantis and Parktown Prawn AKA King Crickets.

I have removed the Non-Celebrity Insects post as no one reads it, but I have broken it up into individual profiles, so their easier to read and find (this will be the Praying Mantis, Parktown Prawn and Wasps posts so far- there is a lot still to cover) J

I am in the process of writing a new post under the new section of Diseases, Disorders and Pests (Index and Info) so be on the lookout! J


Oh! A warm welcome to the newest follower! I hope you enjoy the articles. J


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