DISTRIBUTION AND PARASITIZATION OF COCOONS OF THE DOUGLAS-FIR TUSSOCK MOTH, HEMEROCAMPA PSEUDOTSUGATA (LEPIDOPTERA: LYMANTRIIDAE), IN AN ISOLATED INFESTATION

Abstract

Douglas-fir tussock moth cocoons were collected and their distribution recorded by crown level on white fir, Abies concolor, in northeastern California. Nine trees were sampled in two defoliation classes, light (20–30% defoliated) and moderate to heavy (50–80% defoliated). Cocoons were more abundant in the lower crown levels as defoliation became greater. The proportion of female cocoons increased toward the lower levels of the crown. An overall sex ratio of 1.2♂:1.0♀ was recorded. Significantly more male cocoons were parasitized than female. A list of the natural enemies of the tussock moth from the study area is given.

Pest Management of Douglas-Fir Tussock Moth (Lepidoptera: Lymantriidae): A Sequential Sampling Method to Determine Egg Mass Density

“…Condrashoff and Grant (1962) and Mason (1970) found the same trend with egg masses associated with nil or trace amounts of defoliation and that this trend reversed when defoliation became heavy. Condrashoff and Grant (1962) also found the same trends with female cocoons but Luck andDahlsten (1967, 1980) and Dahlsten et al (1970) reported that egg masses and female cocoons were concentrated in the lower crowns even when no or trace amounts of defoliation prevailed and this concentration increased with heavier defoliation. The vertical trend in egg-mass distribution was not consistent from plot to plot when egg-mass density was expressed on a per-branch basis (Table I); there were highly significant crowns x plots and crowns x trees (within plots) interactions.…”

“…Also, situations were encountered where there was an apparent collapse in the viability of the population during the pupal stage and, although many cocoons were found, the proportion bearing egg masses was quite low. An additional complication in sampling cocoons is the differential mortality and distribution between the sexes (Condrashoff and Grant 1962;Dahlsten et al 1970;Luck and Dahlsten 1980). Cocoons were, therefore, dropped from the proposed detection system.…”

EFFECTS OF RESIDUES OF CHITIN-SYNTHESIS INHIBITORS ON EGG HATCH AND SUBSEQUENT LARVAL ENTRY OF THE CODLING MOTH, CYDIA POMONELLA (LEPIDOPTERA: OLETHREUTIDAE)

“…These were 4.0, 8.2, 8.7 and 4.9 for the upper, middle and lower crown, and lowest whorl, respectively (Table I). Condrashoff and Grant (1962) also found the same trends with female cocoons but Luck andDahlsten (1967, 1980) and Dahlsten et al (1970) reported that egg masses and female cocoons were concentrated in the lower crowns even when no or trace amounts of defoliation prevailed and this concentration increased with heavier defoliation. When branch surface area was taken into consideration, the average densities were 6.5, 5.9, 3.9 and 1.7 egg masses per m2 for the upper, middle and lower crown and lowest whorl respectively, indicating a reverse trend.…”

“…An additional complication in sampling cocoons is the differential mortality and distribution between the sexes (Condrashoff and Grant 1962;Dahlsten et al 1970;Luck and Dahlsten 1980). However, no means for distinguishing between cocoons of previous and current generations was found.…”

COMPARISON OF ARTIFICIAL PUPATION SHELTERS AND OTHER MONITORING METHODS FOR ENDEMIC POPULATIONS OF DOUGLAS-FIR TUSSOCK MOTH, ORGYIA PSEUDOTSUGATA (MCDUNNOUGH) (LEPIDOPTERA: LYMANTRIIDAE)

“…Cocoons were collected in fall after adult emergence, whereas egg masses were left in the shelters and collected the following spring, to allow egg parasitization to occur in the field. Cocoon sex and parasitization were determined in the laboratory (methods described in Dahlsten et al 1970).…”