Effects of Fertility Control on Behavior and Disease Transmission in Brushtail Possums

Abstract: Fertility control is currently under development for the control of brushtail possums (Trichosurus vulpecula), one of New Zealand's most serious vertebrate pests. Despite intensive research into various methods for achieving infertility, including immunocon-traception and disrupting endocrine control of reproduction, researchers know little about the potential effects of these methods on the behavior of wild possums. We assessed the effects of surgically imposed sterility, either to block fertilization (tubal ligation) or to disrupt endocrine control of fertility (gonadectomy), by using radiotelemetry on the movement patterns and site fidelity of wild brushtail possums. In addition, we assessed the effect of gonadectomy on the transmission rate of a commonly occurring, directly transmitted pathogen in possums, Leptospira interrogans serovar balcanica (hereafter L. balcanica), to determine the effect of any behavioral changes on possum contact rates. Both tubal ligation and gonadectomy of females did not appear to have any appreciable effect on behavior, with sterilized females having space-use patterns and fidelity to seasonal breeding ranges similar to those of fertile females. However, gonadectomy of male possums resulted in a significant reduction of 42% and 47% in the 95% and 70% isopleth seasonal breeding ranges, respectively. Furthermore, the transmission rate of L. balcanica in gonadectomized male and female possums was reduced by 88% and 63%, respectively, compared with that in fertile male and female possums. Overall, these results suggest that fertility control, either by blocking fertilization (e.g., immunocontraception) or by disrupting endocrine control of reproduction (e.g., gonadotropin-releasing hormone vaccines), is unlikely to have an impact on social organization and behavior of brushtail possums in ways that may compromise the efficacy of fertility control for reducing population density. However, the reduction in the transmission rate of L. balcanica indicates that fertility control that interferes with endocrine control of reproduction is likely to reduce the contact rate between possums. This could have implications for the control of other wildlife diseases requiring direct contact for transmission.     

The impacts of predators and parasites on wild bumblebee colonies

1. The study of wild bumblebee nests has been hindered by the difficulty in locating and observing them. Here, 47 wild nests were located using a sniffer dog and volunteers. The entrances to 32 nests were filmed continuously to identify successful nests (those that produced gynes) and observe vertebrate species interactions. 2. Of the 47 nests, 71% and 21% produced gynes in 2010 and 2011, respectively. 3. A total of 39 vertebrate species were filmed at entrances but the majority did not interact with the nests. Great tits (Parus major) depredated or attempted to depredate bees on 32 occasions at the entrances to 10 nests, something that has not previously been described. Small mammals were very often recorded accessing entrances to bumblebee nests, but whether they depredated bees was not known, and frequently visited nests were no less likely to produce gynes. Eight nests were entered by adult wax moths, Aphomia sociella. 4. The faeces of 1179 workers from 29 Bombus terrestris nests were screened microscopically for parasites. Crithidia bombi infections were apparent in 49% of worker bees, while Nosema bombi and Apicystis bombi were present in 5.5% and 0.68% of bees, respectively. Nests with a high prevalence of C. bombi infection were less likely to produce gynes, the first evidence of a direct impact of this common parasite on bumblebee colony reproduction in wild nests. 5. Overall, our data indicate that bumblebee nests are at the heart of a rich web of interactions between many different predator and parasite species.     

Physical and anthropogenic factors predict distribution of the invasive weed Tradescantia fluminensis

The increasing need to manage plant invasions has generated international interest in predicting the dispersal of invasive weeds, including the role of humans due to the influence of anthropogenic factors on invasions. Tradescantia fluminensis, an invasive weed, is spread in New Zealand only by vegetative fragments, with long‐distance dispersal thought to be largely by human dumping of garden waste. Here we test whether the occurrence of T. fluminensis is predictable from physical (slope, altitude, temperature, vegetation type and cover and stream presence) and anthropogenic (road surface type, proximity to settlement and proxies for ease of dumping) variables, to measure the influence humans exert on its dispersal. Sampling of both physical and anthropogenic variables was carried out with presence/absence of T. fluminensis noted at 151 sites throughout the Marlborough Sounds in New Zealand. The best model included four anthropogenic and three physical variables, with the anthropogenic variables accounting for 70% of the deviance explained. K‐fold cross‐validation showed the model had a success rate of 78%, correctly predicting 118 out of 151 observations. This was significantly better than a null model based only on the overall fraction of sites with T. fluminensis. These results indicate that within the Marlborough Sounds region, anthropogenic factors play a strong role in the dispersal of T. fluminensis in ways that are amenable to predictive statistical modelling.     

Seasonal abundance,biting cycle,parity and vector potential of the mosquito Haemagogus equines in Trinidad

Abstract. The mosquito Haemagogus equinus is a known vector of yellow fever (YF) in central America. Seasonal abundance, daily biting activity and the age composition of adult Hg. equinus female populations were monitored weekly during 1981–82 by human collectors on the ground at Point Gourde Forest, Chaguaramas, 16 km west of Port of Spain, Trinidad. 2. Landing collections of Hg.equinus showed diurnal activity from 06.00 to 20.00 hours (suntime), with a single peak between 08.00 and 14.00 hours. 3. Overall, 5.6% of Hg.equinus were collected during the dry season (December-April) and 94.4% during the wet season (May-November). 4. Mean density of Hg.equinus in relation to man ranged from 0.35/man-day in February to 133/man-day in July, with averages of 2.8 in the wet season, 36.9 in the dry season and 22/man-day for the whole year. 5. Monthly parous rates averaged 62.1% (range 0-88%); 2.8% of females were 2-pars, another 2.8% were 3-pars, but no older females of Hg.equinus were found (sample size 467). 6. These age-grading data indicate that Hg.equinus females have relatively short life expectancy and hence low vector potential, which may help to explain why YF virus has seldom been isolated from this vector species.     

Variations in the resistance to Heterodera rostochiensis of potatoes derived from Solarium tuberosum ssp. andigena and S. multidissectum

The proportion of larvae from ten populations of Heterodera rostochiensis Woll. that became female was determined on five potato clones containing genes for resistance derived from S. tuberosum ssp. andigena., on three with genes from S. multidissectum and on four with genes for resistance from both sources. Variations in the resistance of the clones bred from andigena, especially to two of the populations, suggest the presence of more than one gene for resistance.     

Seasonality, biting cycle and parity of the yellow fever vector mosquito Haemagogus janthinomys in Trinidad

1. Age composition, seasonal abundance and diel patterns of landing activity of the sylvan vector of yellow fever Haemagogus janthinomys Dyar were monitored weekly during 1981-82 by human collectors on the ground at Point Gourde in Chaguaramas Forest, 16 km west of Port of Spain, Trinidad. 2. Landing collections of Hg. janthinomys showed only diurnal activity, from 06.00 to 18.00 (sunrise to sunset, universal time), with a single peak of activity between 10.00 and 16.00 hours. 3. Densities of Hg. janthinomys were about 6 times greater during the wet season (May-November) than during the dry season (December-April); the annual Williams' mean landing rate on two collectors was 9.3 per day. 4. Monthly parous rates averaged 59% (range 0-86%) and some females were up to seven-pars. Retained eggs (range 1-21, mean 7.7/female) were found in the ovaries of 1.3% of landing females, all of which had stage I ovarian follicles for the next gonotrophic cycle. Hence blood-feeding is not inhibited by egg retention, which might promote transovarial transmission of virus. Implications of these findings are discussed in relation to yellow fever epidemiology.