Biology and host preference of Selitrichodes neseri: A potential biological control agent of the Eucalyptus gall wasp,Leptocybe invasa

Selitrichodes neseri (Hymenoptera: Eulophidae) is a parasitoid of the invasive gall-forming wasp Leptocybe invasa (Hymenoptera: Eulophidae), which has caused serious damage to Eucalyptus plantations in many parts of the world. S. neseri is a recently discovered parasitoid considered to be a potentially important biological control agent of L. invasa. The aim of this study was to provide the first basic data on the biology of S. neseri, which is essential for its application in biological control. S. neseri was shown to be a biparental ectoparasitoid. Observation from dissected galls indicated that the parasitoid developed on late larvae, pupae and callow adults, although development did occur in a range of gall ages. Observed nominal parasitism in captivity ranged from 9.7% to 71.8%. Adult S. neseri specimens, fed with honey-water and galled Eucalyptus leaves, survived an average of 26 days at 26 °C. The average developmental time from oviposition to emergence was 19.3 days ± 0.2 days. There was no pre-oviposition period. A single female produced a maximum of thirty-nine offspring, with a maximum of ten per day. Dissection of the ovaries showed that twelve ovarioles were present. The sex ratio of S. neseri observed in this study was 1:3.43 males:females. Galls of native insects most closely related to L. invasa and to galls of similar morphology to L. invasa-induced galls, were not suitable for S. neseri oviposition. S. neseri showed considerable potential as a biological control agent of L. invasa due to its relatively short developmental time, long adult life span when supplemented with carbohydrates, ability to utilize a range of gall ages and the fact that it has a high level of host specificity.     

A search for quantitative trait loci for ovulation rate in cattle

Seventy-seven polymorphic microsatellites were analysed in offspring of three elite sires that were part of the foundation of an experimental population selected for twinning rate at the US Meat Animal Research Center, Clay Center, Nebraska. All females were assessed for ovulation rate by rectal palpation of corpora lutea over 8–10 consecutive oestrous cycles from approximately 12 to 18 months of age, and associations between ovulation rate and sire allele were examined in each of the three sire groups. A preliminary analysis was performed using selectively genotyped daughters of each sire. Markers found significant or approaching significance were also genotyped in all daughters, sons and granddaughters of these sires. A test of marker associations limited to the granddaughter data provided an independent confirmation of marker effect and significance relative to the initial test with daughter data. Putative ovulation rate quantitative trait loci were detected on chromosomes 7 and 23. Marker UWCA20 on chromosome 7 was associated with an effect in excess of one phenotypic standard deviation and accounted for approximately 10% of phenotypic variation ovulation rate. Marker CYP21 (steroid 21-hydroxylase) on chromosome 23 was associated with an effect of slightly less than half a phenotypic standard deviation and accounted for approximately 4% of phenotypic variation.     

Change of liver metabolism of 1,2-dibromoethane during simultaneous treatment with carbon tetrachloride

The combination of carbon tetrachloride (CCl₄) and 1,2-dibromoethane (DBE) in isolated rat hepatocytes led to a significant potentiation of both lipid peroxidation and of plasma membrane damage observed after a single treatment with CCl₄. Such a synergistic effect appeared to be related to the CCl₄-induced shift of DBE metabolism from the cytosolic conjugation with glutathione towards the microsomal transformation into toxic intermediates. In fact, CCl₄ significantly inactivated hepatocyte total GSH-transferase, i.e. the DBE detoxification pathway. Furthermore, while the microsomal metabolism of CCl₄ was not affected by the simultaneous presence of DBE, the amount of DBE reactive metabolities covalently bound to hepatocyte protein was significantly enhanced in the presence of CCl₄.     

On the Information Matrix of Exponential Mixture Models with Long-term Survivors

The aim of this paper is to study the properties of the asymptotic variances of the maximum likelihood estimators of the parameters of the exponential mixture model with long-term survivors for randomly censored data. In addition, we study the asymptotic relative efficiency of these estimators versus those which would be obtained with complete follow-up. It is shown that fixed censoring at time T produces higher precision as well as higher asymptotic relative efficiency than those obtainable under uniform and uniform-exponential censoring distributions over (0, T). The results are useful in planning the size and duration of survival experiments with long-term survivors under random censoring schemes.     

Tradeoff between height and relative growth rate in a dominant grass from the Serengeti ecosystem

We determined the relationship between plant height and whole-plant relative growth rate (g g^-1 day^-1) for ten genotypes of Sporobolus kentrophyllus collected from an intensively grazed site on the Serengeti Plains, Tanzania. Plants were grown for 7 weeks in a greenhouse in Syracuse, N.Y., and harvested weekly. Plants that received simulated bovine urine showed a negative relationship between plant height and growth rate, suggesting a genetic tradeoff between competitive ability if ungrazed (height) and ability to recover from grazing (growth rate). There was no height-growth rate relationship under nitrogen addition rates similar to field mineralization rates. In addition, faster-growing, shorter plants tended to have relatively higher above-ground growth rates than slower-growing, taller plants. These results suggest that natural selection has maintained a gradient of morphologies within this species ranging from short, rapidly growing genotypes adapted to intense grazing conditions to tall, slow-growing, grazer-susceptible genotypes that are superior light competitors in absence of herbivory.     

ESTIMATING NATURAL MORTALITY RATE IN REPRODUCTIVELY ACTIVE FEMALE SOUTHERN RIGHT WHALES, EUBALAENA AUSTRALIS

Cow-calf pairs of southern right whales on the South African coast have been photographed in aerial surveys in October each year since 1979. In this paper 469 resightings of 177 individually identified cows photographed in the first six years of surveys have been analyzed in two ways to produce estimates of natural mortality rate. Both methods assume that all females calve either two, three, or four years after their previous calf. In Method A there is assumed to be no systematic trend with time in the probability of a female being photographed on each calving occasion. Natural logarithms of the numbers photographed 2-4, 5-7, 8-10, etc. yr after being first seen are regressed against time, the slope of which provides an estimate of natural mortality rate of 0.0255 ± 0.0071. The intercept value for this regression provides an estimate of the detection probability, or 0.769 ± 0.011. In Method B it is assumed that if a female has not been photographed for at least nine years then it is dead. Annual mortality estimates are obtained from the proportional reduction in the numbers of females known to be alive at each three-year interval after being first photographed, up to at least 6-8 yr from the present. Method B produces an estimate of natural mortality of 0.0260 ± 0.0190 (corrected to 0.0227 ± 0.0192 using the average detection probability). Both methods may be subject to various biases that tend to inflate estimates of natural mortality.