Oak worm outbreak 2007 - 2007/08/30 09:34
Hi All,
In case you were wondering what's up with all those crazy caterpillars dangling from oak trees, getting in your face, covering your shirt, etc., below I've pasted bits and pieces from excerpts found on the web. There is some repeated information, but it's a quick read.
Cheers,
Steve
The California oakworm, Phryganidia californica, is one of many species of caterpillar that feed on oaks in California. Damage is most common on coast live oak, Quercus agrifolia, in the San Francisco Bay Area and Monterey Bay region with outbreaks occurring at about 8- to 10-year intervals; however, outbreaks can occur in many parts of the state.
IDENTIFICATION
The adult is a uniformly tan to gray moth distinguished by its prominent wing veins. Unlike females, males have feathery antennae. The female lays tiny round eggs in groups of about two or three dozen on twigs or leaves. The eggs are white but develop red centers that become pinkish to brownish gray before hatching.
The young larvae are yellowish green with dark stripes on their sides and have large brown heads. Mature larvae are variable in color, but commonly dark with prominent lengthwise yellow or olive stripes. Larvae range in size from 1/10 inch long when newly hatched to about 1 inch when fully grown. Pupae are white or yellow with black markings, 1/2 inch long, and are found suspended from limbs or leaves, on the bark, or on objects near trees.
The California oakworm excretes droppings (frass) that fall to the ground beneath the tree. As larvae grow, fecal pellets increase in size. Greater numbers of pellets are produced with an increase in the number of larvae or an increase in temperature, which ca
Young larvae skeletonize the leaf surface, while older larvae chew all the way through the leaf. Defoliation on live oaks may become extensive in May or June and again in July through September. Healthy trees can tolerate some damage; by comparison, trees under stress from drought or other factors may decline if defoliated.uses caterpillars to feed faster.
Mature worm larvae are found on the Central Coast from May to June and adults emerge June to July. The worms quickly go to work feeding on oak trees. They have a hefty appetite for leaves, and in no time a healthy oak tree can be left practically naked.
The worms don’t kill trees, but defoliation can leave them looking sickly.
Lack of rain in the winter and spring created ideal conditions for an eruption in the oakworm population, experts say.
Cold, damp weather tends to kill the female moth eggs, which are laid on the underside of leaves and later hatch into the worm.
The oakworm is not to be confused with the light brown apple moth, a noted pest in Santa Cruz County that destroys young seedlings, spoils the appearance of ornamental plants and damages fruit.
Normally, this area sees two life cycles of oakworms, but the warm dry weather has spawned a recent third generation, which is extremely rare, according to arborists.
The larva, or caterpillar, is responsible for the damage to oak trees. The young oakworm caterpillar is hairless and yellowish-green with dark stripes and has a head that appears too big for its body. Mature caterpillars are mostly black with prominent stripes. With warming temperatures and the new flush of leaves in spring, the tiny caterpillars begin feeding in earnest on the new foliage. You may see hundreds eating leaves, hanging on fine silk threads from oak trees, moving on the ground, even on your house. After about 6 weeks, the caterpillars become adults, a brown moth. The adults do not eat but live only to mate and lay eggs. This whole process, egg to adult, occurs two or three times per year. Depending on the duration of warm weather, oakworms can be active from early spring to late fall.
The life-cycle of the oak moth includes two and occasionally three generations per year. In most of California there are usually two broods per year -- a long-lived winter generation and a short-lived summer cycle. The first set of eggs hatch in late fall, and the small caterpillars overwinter on the undersides of oak leaves. Mature larvae are found from May to June, and adults emerge June to July. The eggs of summer adults hatch soon after, and the cycle is completed with the emergence of adults in early fall.??Periodic outbreaks occur approximately every 5 – 10 years, and in the most extreme cases lead to severe oak defoliation of some trees. During these outbreaks caterpillars are often seen suspended from cobwebby strands (perhaps using the silk as a lifeline or to anchor to twigs while consuming the underlying leaf platform). Healthy oaks appear to recover from these periodic defoliation events, but oaks that are simultaneously subjected to other stresses of drought, soil compaction, fungal infections (e.g. Sudden Oak Death Syndrome), and bacterial infections may be more seriously affected by oak moth defoliation. Biochemical and physiological defenses of oaks help to resist insect attack. This resistance, however, may vary between individuals of the same species and might explain why neighboring trees exhibit widely varying amounts of defoliation. Other potential factors which may indirectly affect susceptibility include the age and condition of an oak (whether it is diseased or drought-stressed) as well as human impacts (e.g. pruning, damage to roots associated with construction or vehicle traffic, altered drainage patterns, and so on).
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