Abstract:The combination of biochar (BC) with compost has been suggested to be a promising strategy to promote plant growth and performance, but although "synergistic" effects have been stated to occur, full-factorial experiments are few, and explicit tests for synergism are lacking. We tested the hypothesis that a combination of BC and spent mushroom substrate (SMS) has a positive synergistic effect on plant growth and physiological performance in a nutrient-limited growing media. A greenhouse experiment with a full factorial design was conducted using mixed-wood BC (3.0 kg·m −2 ) and SMS (1.5 kg·m −2 ) (the combination was not co-composted) as organic soil amendments for the annual Abutilon theophrasti and the perennial Salix purpurea. Several measurements related to plant growth and physiological performance were taken throughout the experiment. Contrary to the hypothesis, we found that the combination of BC + SMS had neutral or antagonistic interactive effects on many plant growth traits. Antagonistic effects were found on maximum leaf area, above-and belowground biomass, reproductive allocation, maximum plant height, chlorophyll fluorescence, and stomatal conductance of A. theophrasti. The effect on S. purpurea was mostly neutral. We conclude that the generalization that BC and compost have synergistic effects on plant performance is not supported.

No abstract

Uncertainty about the taxonomic status and the specificity of a species commonly prevent its consideration as a candidate for biological control of pest organisms. Here we use a combination of molecular analysis and crossing experiments to gather evidence that the parasitoid wasp Ganaspis brasiliensis, a candidate for biological control of the invasive spotted wing drosophila Drosophila suzukii, is a complex of at least two cryptic species. Complementary experiments demonstrate that individuals from one genetic group readily parasitize several drosophila species regardless of their food source while individuals from the other one are almost exclusively specific to larvae feeding in ripening fruits. Because only D. suzukii attacks ripening fruits in its area of invasion, parasitoids from this second group appear to be well suited as a biological control agent. Our study demonstrates the need for a combination of biosystematics with biological and ecological investigations for the development of safe and efficient biological control programs.

No abstract

The seasonal pattern of parasitism by a parasitoid can be influenced by many factors, such as interspecific competition and host instar preference. We conducted field and laboratory experiments to describe the seasonal pattern of parasitism of spruce budworm Choristoneura fumiferana (Clemens) larvae by Tranosema rostrale (Brischke), and to investigate whether this pattern can be explained by interaction with other parasitoid species, or by host instar preference. Larval survival, developmental time, sex ratio, and adult size of T. rostrale developing in different host instars were also measured to further assess the potential importance of host instar on parasitoid life history. Parasitism by T. rostrale increased over the season, reaching the highest rate during the fourth-instar larva, and then decreased again until the sixth-instar. At the same time, parasitism by another parasitoid, Elachertus cacoeciae (Howard), increased over the season, and multiparasitism with T. rostrale suggests potential competition between these two parasitoids. Tranosema rostrale showed no host instar preference when third- to sixth-instar larvae were exposed simultaneously in a manipulative field experiment. The proportion of females emerging from spruce budworm larvae increased over the season; however, no difference in sex ratio was observed in the manipulative field experiment. Only male pupal development time and adult size were marginally increased in fifth-instar spruce budworm larvae. We conclude that T. rostrale's seasonal phenology or competition with E. cacoeciae, but not host instar preference, were possibly responsible for the observed seasonal pattern of parasitism.