Recently, Master Gardener Susan M. was toiling away at the demonstration garden on San Juan Island, when she spied what she described as “a little larva/worm that looked like a wire worm”:
I was picking strawberries & one of them had been eaten away by the creatures.
There were several (3-4?); the planter is located next to a columnar apple tree
and a pear espalier tree.
Let’s see…Strawberries…next to an apple…and a pear…Ah-HA!
Susan, them ain’t no run-of-the-mill caterpillars. What you found there are the larvae of:
Light Brown Apple Moth
And it’s no wonder that even we experienced Master Gardeners scratch our heads upon seeing them: Light Brown Apple Moth (Epiphyas postvittana) is a recent arrival to our shores, having first been detected in Alameda County, California in 2006. Originally from Australia, LBAM is also known to be established in New Zealand, New Caledonia, the U.K. and Ireland, and has been reported in Hawaii. Prior to its discovery in California, LBAM had never been detected in the continental U.S.; since then it has spread steadily throughout the Golden State, and continues north- and eastward, in what the California Department of Food and Agriculture called “a new record for the Americas.”
(Eek, right? Hang on, we’re just getting started.)Life Cycle
These moths reproduce with admirable regularity. In their native Australia, they will typically produce three generations per year, with larvae overwintering; in temperate, laid-back, “anything goes” California, it’s been found that up to five generations per year are possible.
Females deposit egg masses containing 20–50 eggs on smooth surfaces of host plants, including leaves, stems, and fruit; in her lifetime, one female LBAM could lay over 400 eggs. The flat, oval eggs can be pale yellow to white and translucent, overlapping (or imbricate) like a mass of shingles or fish scales. They can take 5 to 30 days to hatch, depending on temperature.
Newly hatched larvae have dark heads and pale bodies, hence the resemblance to wire worms, and feed on the undersides of foliage. The mature caterpillar is 10-20mm long, yellowish-green, and a leaf-roller — creating a little nest by folding leaves together with webbing, sometimes attached to fruit (for convenience, maybe?).
The larva will pupate in its webby rolled leaf nest. The adult will emerge in 10-21 days and — surprise, surprise — mate almost immediately; with a life span of no more than three weeks and the weight of all those future generations on its shoulders, it’s no wonder.
LBAM apparently has no winter resting stage (diapause), but cold temperatures slow larval development. The larvae overwinter by feeding on herbaceous plants, buds of deciduous trees or shrubs, mummified fruit and other plant material, and can survive for up to 2 months in the winter without feeding at all.
And there’s more…
Nom Nom Nom!
The USDA has compiled a list of LBAM host plants that contains well over 1,000 — yes, one thousand — plant species, and includes hundreds of fruits and vegetables, meaning this little pest could potentially make a lot of trouble for farmers and food growers.
It’s also no surprise that Susan found them on the strawberries, near the pear and apple trees: LBAM’s culinary favorites tend to be berries and tree fruits. They are rather the little gourmands, however, and will also take to almond, avocado, oak, willow, walnut, poplar, cottonwood, Monterey pine and eucalyptus trees, as well as corn, pepper, tomato, pumpkin, beans, cabbage, carrot, alfalfa, rose, camellia, pittosporum, jasmine, chrysanthemum, clover, lupine and plantain.
Jeez, if only we could get our kids and spouses to eat this well.
How Can I Tell If I’ve Got ‘Em?
Like caterpillars in general, LBAM larvae will feed on foliage, but they really like the fruit and vegetable crops on our rather extensive list. Look for evidence of chewing on leaves, fruits and veggies; spongy or cork-like tissue on damaged surfaces of crops; or “halo” scars around fruit stems. Young larvae may also enter pome and stone fruits through the calyx. On conifers, look for needle tying, chewed buds and evidence of boring on stems; damage to terminal buds on seedlings and saplings can cause multiple or crooked leaders.
Gah! So What Can We Do?
While large-scale agriculture has found success in controlling LBAM through the use of pheromone traps and the managed release of LBAM parasites, these tactics aren’t exactly available to the home gardener. However, all is not lost: Bacillus thuringiensis (B.t.) has also been effectively used against these invaders, and is commercially available for home gardeners. (B.t. is a naturally occurring biological pesticide and is generally considered safe for other organisms.) Apply B.t. to the foliage once the larvae are actively feeding; the caterpillars will sicken, stop eating, and die within days. (By the way, WSU advises homeowners to consult a professional for treatment of trees or shrubs above 10 feet tall.)
And of course, you are often your own best pest control — so hand-harvest those caterpillars, squish those egg masses, clean out those rolled leaves, and swat those moths! LBAM? NIMBY!
For more information on this new exotic invasive pest, visit our sources: the University of California Dept. of Agriculture and Natural Resources; UCANR Bug Squad; California Dept. of Food and Agriculture; USDA Animal and Plant Health; and the WSU Tree Fruit Research and Extension Center.
And if you’re a San Juan County gardener in need of help with a plant or insect identification and diagnosis, contact us.
Egg mass photo courtesy USDA
All other photos courtesy University of California Dept. of Agriculture and Natural Resources