Efficient production of male Wolbachia-infected Aedes aegypti mosquitoes enables large-scale suppression of wild populations

The range of the mosquito Aedes aegypti continues to expand, putting more than two billion people at risk of arboviral infection. The sterile insect technique (SIT) has been used to successfully combat agricultural pests at large scale, but not mosquitoes, mainly because of challenges with consistent production and distribution of high-quality male mosquitoes. We describe automated processes to rear and release millions of competitive, sterile male Wolbachia-infected mosquitoes, and use of these males in a large-scale suppression trial in Fresno County, California. In 2018, we released 14.4 million males across three replicate neighborhoods encompassing 293 hectares. At peak mosquito season, the number of female mosquitoes was 95.5% lower (95% CI, 93.6-96.9) in release areas compared to non-release areas, with the most geographically isolated neighborhood reaching a 99% reduction. This work demonstrates the high efficacy of mosquito SIT in an area ninefold larger than in previous similar trials, supporting the potential of this approach in public health and nuisance-mosquito eradication programs.

Investigating light-use efficiency across a jack pine chronosequence during dry and wet years

Light-use efficiency (LUE) is the ability of vegetated canopies to use light for photosynthesis. Together with remote sensing estimates of canopy cover and meteorological inputs, LUE provides a physical basis for scaling carbon uptake processes from the stand to the global scale. A better understanding of the factors that control LUE will result in improved global estimates of carbon uptake from the terrestrial biosphere. To examine factors that control variability in LUE in stands of different ages during dry and wet conditions, we measured LUE in a chronosequence of four jack pine stands (recent clearcut (age 1-3), regenerating (age 8-9), immature (age 29-30) and mature (approximately 90 years old)) during one normal (2002), one very dry (2003) and two very wet (2004, 2005) growing seasons in Saskatchewan, Canada. Cumulative CO(2) fluxes decreased significantly at all sites during the drought year of 2003, as did mean LUE. Canopy foliage at the recently regenerating jack pine site increased by 19% between 2002 and 2003. Foliage growth rate was reduced by 6% between 2003 and 2004, and foliage biomass decreased by 6% from 2004 to 2005. Over the four years studied, LUE was greatest at the mature jack pine site and lower, but similar, at the other three sites. Mean growing-season LUE varied with mean soil water content at each site, except at that of the newly regenerating stand where soil water had little influence. Mean daily vapor pressure deficit typically had the greatest influence on variability in LUE at all sites. Diffuse versus direct radiation also had significant but varying effects on LUE in jack pine stands of different ages.

Effects of elevated carbon dioxide concentration and temperature on needle growth, respiration and carbohydrate status in field-grown Scots pines during the needle expansion period

We determined effects of long-term elevation of carbon dioxide concentration ([CO2]) and temperature on growth, respiration and carbohydrate concentration in needles of field-grown Scots pine (Pinus sylvestris L.) trees during the needle expansion period. Sixteen 20-year-old Scots pine trees were individually enclosed in closed-top, environmentally controlled chambers for 4 years in one of four environments: ambient conditions (CON); elevated [CO2] (EC); elevated temperature (ET); and a combination of both (EC + ET). Needle growth, carbohydrate concentration and dark respiration were measured at 3-day intervals throughout the needle expansion period. Dark respiration was partitioned into growth and maintenance components by regressing specific respiration rate against specific growth rate. In all treatments, growth, carbohydrate concentration and daily dark respiration rates of needles followed a similar seasonal pattern throughout the needle expansion period. Treatments EC, ET and EC + ET increased individual needle area and dry weight compared with the CON treatment. Carbohydrate concentrations in needles were increased by EC, but reduced by ET and EC + ET. Daily respiration rates increased slightly in the early stage of needle expansion and decreased gradually in the late stage when needles were exposed to EC, but increased consistently throughout the growing period when needles were exposed to ET or EC + ET. Partitioning of respiration into its two functional components showed that the growth respiration coefficient was unaffected by the treatments, whereas maintenance respiration was reduced by EC but increased by ET and EC + ET. Maintenance respiration was more sensitive to elevated temperature than growth respiration. We conclude that the difference in respiration rates between expanding and expanded needles should be taken into account when estimating the respiratory responses of needles to elevated [CO2] and temperature.