Looper Caterpillars

This is one of the culprits responsible for the recent damage to my veggies. They are Vegetable or Green Loopers (Chrysodeixis eriosoma)*.  Their “loopy” name is because of the way they move -  they lack legs in the middle of their bodies so when they walk they hunch up in the middle, forming a loop.

When small they are green all over, but develop stripes as they get older, and can grow up to 4cm long. The amount of time they spend as larvae or caterpillar form, varies from 2 to 4 weeks, depending on the temperature, and the quality and quantity of food available.

Vegetable loopers feed on a wide range of plants, and mainly consume the leaves, but they will also attack  fruits, like tomatoes or beans, and flowers.  When small the larvae feed on only one side of the leaf, leaving translucent feeding windows, but as they develop, they chew holes in the leaf, and along the leaf margin, down to the central ribs. 

Control of Green Loopers (Chrysodeixis species)

Commercial crops, especially ones that are not used for their leaves, such as beans or peas, are often not treated as the amount of damage due to defoliation can be tolerated. 

For home gardeners the best method is manual removal of caterpillars, which is easiest when they are active in the cooler parts of the day.  To save your crop, early detection, before they can destroy too many leaves is going to be needed. (although its fine to eat the remainder of the leaves they have chewed holes in).  The removal of cocoons and eggs also helps.

The caterpillars cleverly lie along the veins of leaves and can blend in amazingly well. Look for holes, or the windows that the smaller caterpillars make. Piles of their droppings can be another clue to track them down. They spin loose cocoons on the back of leaves which are easy to remove.

Most general insecticides will kill them, but because they have a lot of natural predators, such as parasitoids, some bugs, spiders, lacewings, ladybird beetles and other predatory beetles, that may also be killed in the process, using them may not reduce the presence of caterpillars in the long run.  Products such as Dipel (Bacillus thuringiensis (Bt)) while being a better choice, because it is more selective to caterpillars, will only work when Vegetable Loopers are small (less than 12mm).

Other Organic Controls

• Keep plants healthy with fertilisers and Seasol (seaweed liquid) - Vigorously growing plants will be better able to compensate for flower and fruit damage, and damaged leaves will be replaced more quickly.  
• On healthy plants caterpillars will need to eat less and move on from the larvae stage more quickly, so the damage is less (but presumably once they become moths they will come back and lay their eggs again more quickly)
• Good plant spacing (between the same species, or others that the loopers prefer) can reduce the transfer of caterpillars (and make spraying easier if necessary).
• Removal of unhealthy or finished plants and leaves to limit transfer of caterpillars.
• Trap crops - sacrificial plants that the loopers prefer.  The caterpillars eat them instead.  They must be removed once infested before caterpillars start to look elsewhere. Gardening Australia have a Fact sheet about these and dead end trap crops here.
• Reduce access by moths so they can't lay eggs in the first place, or by caterpillars, with plant netting or fruit bagging.
• Plant Resistant varieties - different forms, colour, natural chemicals, cell thickness or leaf surface coverings can make a difference to plant susceptibility or how much is consumed if attacked.

Links for more details and further advice about Looper control:

• Gardening Australia Fact sheet: Friends and Foes
• Gardening Australia Fact sheet on Caterpillar Control
• Loopers in field crops - Queensland Department of Agriculture, Fisheries and Forestry
• Ausveg article on Caterpillar Control
• T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network - Chrysodeixis eriosoma (Green garden looper)

Note: No caterpillars were harmed in the taking of these photographs. (However they were humanely squashed soon after)

* I think these are (Chrysodeixis eriosoma), but they might also be Tomato Loopers (Chrysodeixis chalcites). Entymologists, who would be qualified to judge the difference, are unsure whether the two species might actually be allotropic and conspecific - which would mean they have developed differences as a result of having bred in isolation from each other, but they are the same species. 

And now, a vintage technical illustration to end with: