Roots 'n' Shoots: Caterpillars - Garden Pest of the Month

Saturday, 26 April 2014

Caterpillars - Garden Pest of the Month

Caterpillars at a glance

Type of Damage
Chewing
Plant Symptoms
Holes in fruits, missing leaves, eaten leaves, ‘felled’ seedlings
Favourite Plant
Most food crops, especially tomatoes, fruit trees, grapes, citrus, sweet potato, Solanum family
Control
Biological (predators: wasps, mantids, assassin bugs & chickens), else physical removal


Caterpillar morphology
Quick Intro

Caterpillars are regarded as one of the most destructive insect pests that can devastate a food crop overnight! Some are specialists only feeding on certain host plants whereas other are generalists and will feed on anything green. Here I discuss some of the caterpillars that have cause havoc in my garden and listed a few similar species to be on the lookout for.

Science Stuff

Caterpillars are the larval or immature stages of moths and butterflies; these belong to the Lepidoptera order of insects. Sometimes caterpillars are referred to as worms, but they are not true worms (Annelida), such as earthworms.

Caterpillar is a derivative from the Latin words cattus (cat) and pilosus (hairy), which basically translates to hairy cat J. Many caterpillars are indeed hairy, which irritate the skin or mucous membranes of would-be predators. Some are even toxic as they sequester poisons in their bodies from compounds in their host plants. Toxic caterpillars display their toxicity through bright colouration, whereas other relies on camouflage for protection.

Alice and the Caterpillar

Interesting morphological characteristics: the last few segments on the caterpillar’s body have fleshy sucker-like legs, known as prolegs, with which they cling to substrates. They have silk glands, which are modified salivary glands mainly used to produce silk for pupation and cocoon construction.

Habitat & Feeding

Adults (butterflies and moths) are generally nectar feeding, whereas larvae are herbivorous and some species are insectivorous or detrivores.

The main objectives of caterpillars are to feed and grow. They are gregarious and feed in groups to ensure safety. Caterpillars feed on the underside of leaves, so be sure to check there when you are on the hunt. Caterpillars moult several times throughout their life as they grow (4-5 times). Plump caterpillars spin cocoons (silk) or pupate in chrysalis (non-silk). Here they undergo metamorphosis into their final butterfly or moth stage.

Caterpillars occupy a wide variety of environments and many have cosmopolitan distribution, which means you are likely not going to get away from them…

Diseases

Generally caterpillars don’t transmit plant diseases, but secondary bacterial, fungal or virus infections can set into affected sites which, have been eaten or stung (fruits and leaves). Holes eaten in fruits can become homes for other insects as well!


Citrus Swallowtail Butterfly, Papilio demodocus

Caterpillars of this family have large, striking butterflies of the Papilionidae family more commonly known as the Swallowtails. They have several district immature stages with different appearances, but all feed on citrus or members of the Rutaceae plant family (lemons, oranges and rue include a few).

Early stage caterpillars are black and spiny with white or orange patterns, this gives them a bird-dropping characteristic. Larger caterpillars lose these markings and become green with the classic swallowtail morphology; large eyespots on the head and thick fleshy body. All stages have a specialised scent gland (technical term, osmeterium) which is concealed behind the head and used as a defence mechanism. When disturbed they whip it out and try to stink you away! They pupate in chrysalis suspended by silk threads.

I had several infestations, they seem to come in waves, over the course of summer. They feed on any Rutaceae plant member, since I found them on my lemons, limes and curry plant!

Citrus swallowtail caterpillar two immatures,
Papillio demodocus

Citrus swallowtail caterpillar,
Papillio demodocus

Citrus swallowtail caterpillar osmeterium,
Papillio demodocus
Citrus swallowtail butterfly,
Papillio demodocus

Citrus swallowtail butterfly,
Papillio demodocus

Similar species in South Africa:
Mocker swallowtail (Papilio dardanus), Green-banded swallowtail (Papilio nireus).

Other similar species:
Citrus butterflies (Papilio anactus, Papilio eageus)


Green-striped Hawkmoth (Grapevines), Theretra jugurtha

Hawk or sphinx moths are very easy to spot with their streamlined bodes and large googly eyes. They are members of the Sphingidae family and the adults are active at dusk and feed on nectar. Larvae are hairless, bright green with a distinctive tail hook and pronounced eyespots. They pupate in the soil or under leaf litter in chrysalis.

Hawk moth caterpillars are fruit lovers, feeding either on fruiting bushes, vines or trees. They are often pests in orchard with damage to grapevines being severe. I also had huge infestations of these guys that came at my grapevine in waves! I only have one grapevine, so it goes to show how well the adults can sniff out grapevines on which to lay eggs. Be vigilant for these caterpillars if you have grapevines because they can destroy a plant within a few days before you even notice it (especially when you have had a lot of hail and you assume chewed leaves to be hail damaged leaves J).


Green  striped Hawkmoth large caterpillar on grape vine,
Theretra jugurtha


Green striped Hawkmoth large caterpillar,
mature ready to pupate,
Theretra jugurtha
Green  striped Hawkmoth,
Theretra jugurtha
Green  striped Hawkmoth,
Theretra jugurtha

Similar species in South Africa:
Cape Hawk/Grapevine Hawkmoth (Theretra capensis)

Other similar species:
Vine hawkmoth/silver-striped hawkmoth (Hippotion celerio)

Vine hawkmoth Hippotion celerio


Tomato semi-looper, Chrysodeixis acuta

Owlet moths from the Noctuidae (Agrotidae) family are highly destructive as adults and larvae. Night-flying adults pierce the skin of fruits which likely succumb to rot. Larvae are highly destructive, feeding on leaves and green fruits causing them to drop or rot or become hosts to other insects! Some species pupate in the soil (chrysalis) whilst others pupate in cocoons spun inside curled up leaves.

Spider has taken residence
in damaged tomato fruits

These are the biggest bane of my tomatoes, eaten leaves and green fruits. They caused about 30% loss in my tomato fruits last year (summer 2013) due to fruit drop or rot. I patrol the tomatoes in summer and check the underside of leaves and between developing fruits, pick of any culprits and feed them to the chickens (- at least I get my tomatoes back in the form of eggs J).


Silver U, Tomato semi-looper caterpillar,
Chrysodeixis acuta

Silver U, Tomato semi-looper pupae and moths,
Chrysodeixis acuta

Similar species in South Africa:
Golden Plusia (Trichopulsia orichalcea), Tomato/Cotton Leaf Moth (Spodoptera littoralis), African army worm (Spodoptera exempta)

Other similar species:
Green looper (Chrysodeixis eriosoma), Cabbage looper (Trichopulsia ni)


Cutworm (Any food crop seedling)

Cutworms are larvae from large groups of moths, Owlets (Noctuidae), who burrow in the soil and sever you seedlings at ground level. Morning reveals their night-time activity by a plot with ‘felled’ seedlings. They are very destructive and wasteful, cutting down an entire stand of seedlings overnight. There are several ways to stem their destruction through adding collars (cardboard) around your plants, starting your plants in pots and potting them out once they are large enough. Otherwise try potash, I think the tiny sharp particles aren’t fun to burrow through see more on my Pest control page. Starvation is another remedy, by leaving plot bare and removing weeds.

Cutworm, Noctuidae species
C-shape


Cutworm damage - a bit too late to put the collar on...


Cutworm collar


 Control

Birds are the main predator of caterpillars, seeing that most wild (black-eyed bulbuls, flycatchers) and domesticated birds (chickens) will do away at your vegetables as well – geese or ducks are more suited to insect pest control as their damage to food crops are minimal.

On the insect side, caterpillars are a favourite of parasitic wasps, but these are more suited to use in green houses (see Wasps post). Otherwise try to design your Insectary to attract paper wasps and mantids to clean out your caterpillar problems.

Biological caterpillar control

Chemical control likely would result in poisoning of other ‘higher’ insects, such as bees, spiders, mantids and wasps. Even organic solutions might affect other insects as well. Therefore, after biological control, I recommend removing them physically by hand and feeding them to the chickens (or put them out for the other birds J).

Preventative tips

The most successful way of limiting caterpillars is by reducing their host plant or making their host plant harder to find. Reduce large stands of one crop type (monocultures) and inter-plant your crops. This was very successful with my tomatoes, which I have had a reduction in crop loss by inter-planting the tomatoes and planting them far apart (limits walkover of caterpillars from one plant to the other).

Holes in tomato,
caterpillar damage by Tomato semi-looper

The best way to ID the caterpillar plaqueing your crops is to grab a few and 'incubate' them. Put them in a container with holes, feed them leaves and let it pupate. Photograph and take notes of the adult. The adult is the main ID stage for caterpillars. Most of the caterpillar here, I incubate in order to ID.

Green  striped Hawkmoth large caterpillar ,
infestation incubation,
Theretra jugurtha


Something cool: Earthwatch Institute

The Earthwatch Institute is a non-profit organisation that promotes research in the nature environment. They allow member of the public (volunteers) to join researchers on field expeditions when they collect samples and field data. You can join a research group by booking online at their website. Expeditions last several days to weeks and members of the public pay for their participation. Money raised through these expeditions is used for further research purposes.

Earthwatch
They have several projects, including ones for documenting caterpillars. They collect data on the biology and numbers of caterpillars in order to study their interaction with other insects, especially their parasitic wasps. The change in global weather pattern influence the rate of caterpillar developments, which in turn shortens the window for the parasitic wasps to locate, lay and develop in the caterpillar themselves. Researchers are interested in studying these dynamics, one such project, includes documenting the caterpillars of Costa Rica, more information on their website: EarthwatchInstitute.


"GRRR!"

Green  striped Hawkmoth large caterpillar on grape vine,
Theretra jugurtha


Related Posts/Pages



Recommended Books for pest control: Natural Pest and Disease Control 




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