– – – – – – – –
BY SUSIE FORK

October 2002: The California Oakmoth (Phryganidia californica, Family: Dioptidae) is a native moth of coastal California and the Sierra Nevada foothills. The tannish brown adults (body length 14–20mm) are commonly seen in the late afternoons from spring through fall as they hover around Coastal Live Oak and other oaks in the genus Quercus that serve as host plant for the larvae. In the Monterey Bay area, these moths are on the wing from approximately June through November. Females lay whitish eggs in clusters on twigs and leaves; the eggs turn reddish or brownish as hatching approaches. Young larvae skeletonize the leaf surface, while mature larvae consume entire portions of the leaf. The mature larvae are 20–30mm long and are olive green with black and yellow longitudinal lines along the back and sides and have a reddish head. The pupae are white or yellow with black markings and are found hanging from bark, leaves, and branches.

Mature oak moth larvae are about an inch long.

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).

An adult oak moth has one mission: make more oak moths.

Predators of the California Oakmoth include birds, spiders, true bugs, lacewing larvae, and ground beetles. These moths are also parasitized by several small wasps and are susceptible to certain insect-specific fungal infections. So, although the oak moths can periodically wreak havoc on certain trees, oaks and oak moths have been coevolving for a long time and can be viewed as one of the many conspicuous insects of the Reserve.