Female Cocoons Research Articles

Season and Intensity of Water Stress: Host-Plant Effects on Larval Survival and Fecundity of Neodiprion gillettei (Hymenoptera: Diprionidae)

A 2 (season of stress) x 3 (stress level) x 6 (host genotype) factorial design experiment was used to examine the influence of host plant stress on larval feeding performance. Total instar survival and female cocoon mass of a pine sawfly, Neodiprion gillettei (Rohwer), were measured under greenhouse conditions in response to feeding on ponderosa pine, Pinus ponderosa Douglas ex Law., seedlings subjected to water stress treatments during either the early-season root growth or early-season shoot growth period. Performance of N. gillettei depended on the growth period in which seedlings were stressed. Performance decreased when larvae fed on seedlings that were subjected to moderate and high stress intensities during the shoot growth period compared with stress treatments during the root growth period. In addition, the potential fecundity of N. gillettei varied among open-pollinated families of ponderosa pine in response to feeding on seedlings that were either moderately or highly stressed during the shoot growth period. Potential fecundity increased in response to larvae feeding on open-pollinated families having a low fine root :current-year foliage ratio compared with families having a high fine root :current-year foliage ratio. This may indicate that differential response for both herbivore and host to water stress is caused in part by a genetic component in the host. Furthermore, the interactions among timing of stress, level of stress and host genotype, shown in this study to influence sawflv performance, demonstrate how different combinations of these factors may result in opposing conclusions concerning the effects of host plant stress on herbivore performance.

Differentiation of Male, Female and Dead Silkworms While in the Cocoon by near Infrared Spectroscopy

The feasibility of using a non-destructive method to differentiate male (M), female (F) and dead (D) worm cocoons of silkworms has been studied with near infrared (NIR) spectroscopy over the region 680–1235 nm on a sample set of 205 fresh cocoons. On the basis of the spectral data of the first and second derivatives, characteristic vectors were extracted by multiple linear regression and a Bayes critical function was established. This function was used to test 375 samples and the success rate was 95.7%. This method of sex judging is thus preferable to the conventional use of the weight and size of a cocoon which achieved a success rate of only 82.9% on the same samples. Experiments showed that the differences between NIR spectra of M and F cocoons mainly result from the property of silkworm cocoons rather than their incunabulum.

The success of pine sawflies in relation to 3-carene and nutrient content of Scots pine foliage

Three species of sawflies ( Gilpinia pallida, Neodiprion sertifer and Diprion pini) were reared on 15 different Scots pine clones, which divided into three groups according to their needle Δ-3-carene contents. Foliar 3-carene content poorly explained the variation in sawfly performance; it only correlated significantly with female cocoon weight of D. pini. Needle moisture, N, Ca, Al and Na concentrations were the best indicators of sawfly success. The negative correlation of N with performance differed from earlier findings. However, because of interaction with other factors, it was difficult to assess a definite effect of any single nutrient.

ESTIMATION OF HEMLOCK SAWFLY (HYMENOPTERA: DIPRIONIDAE) FECUNDITY

AbstractMean fecundity of hemlock sawfly females emerging from cocoons collected on heavily defoliated western hemlock trees was significantly less than fecundity of females collected from lightly defoliated trees. Fecundity was highly correlated with female cocoon diameter and female forewing length, but was most highly correlated with both variables combined. Time-saving double sampling techniques are discussed for determining mean fecundities of new samples when mean cocoon diameter and forewing length are known.

Fecundity and Parthenogenesis of the Yellowheaded Spruce Sawfly, Pikonema alaskensis1

Fecundity of the yellowheaded spruce sawfly, Pikonema alaskensis (Rohwer) was studied in the greenhouse and the field using a bag cage tied over branches of white spruce trees, Picea glauca (Moench) Voss. Dissections of 279, 3–5-day-old females revealed a mean potential fecundity of 83.3 mature eggs. Females caged in the field laid 91.9% of their eggs, but females in the greenhouse laid only 61.7%. Longevity of females was 4–7 days, with 1 ♀ living 18 days. Parthenogenetic eggs developed into males. Peak oviposition in the field occurred when 80% of the new shoots were just barely retaining the bud cap. Female cocoons are significantly wider and longer than ♂ cocoons.

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

AbstractDouglas-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.

SENSORY STIMULI INVOLVED IN THE LOCATION AND SELECTION OF SAWFLY COCOONS BY SMALL MAMMALS

The stimuli responsible for the location and selection of healthy vs. parasitized and diseased sawfly prepupae by Peromyscus maniculalus bairdii Hoy and Kenicott, Sorex cinereus cinereus Kerr, and Blarina brevicauda talpoides Gapper were determined in all phases of the search for buried food. Only olfactory stimuli were involved in the digging, removing, and opening phases, while gustatory stimuli played a part in selection in the eating phase. There were innate preferences and a versions to the gustatory stimuli, but not to the olfactory stimuli. It was only with experience that the animals were able to associate odors from cocoons with the taste of the cocoon contents.The selection of healthy male vs. female cocooned prepupae was also studied. In the digging phase all species dug more holes over the larger female cocoons than over the smaller male cocoons. This selection was not affected by experience and was caused by differences in degree and not kind of odor. In the removing and opening phases S. c. cinereus and P. m. bairdii removed and opened more male than female cocoons, while B. b. talpoides removed and opened more female cocoons. This selection was affected by experience and probably resulted from differences in visual or tactile stimuli. The larger the mammal the greater was the selection for female cocoons.