Malik RJ, Ali JG, Bever JD. Pedobiologia. 2018;66:29-35. doi: 10.1016/j.pedobi.2017.12.004.
While arbuscular mycorrhizal (AM) fungi may have a prominent role in trophic ecology, mycorrhizal improvement or reduction on herbivore growth and survival may also be dependent on herbivore's stage of development. Solanum lycopersicon (tomato) was grown on sterile background soil treated with either mycorrhizal inoculant (AM+) or non-mycorrhizal control (AM-). Mycorrhizal treatments included four single species of AM-fungi (Entrophospora infrequens, Funneliformis mosseae, Claroideoglomus claroideum, and Racocetra fulgida) and a mixture of all four species (fungal community). To determine if mycorrhizal treatment indirectly alters the ability of beetle larvae (Leptinotarsa decemlineata) to access plant resources, plant damage and trichome density were quantified as plants were infested with a single neonate (early-stage) for 96 hours (h). In a second experiment, beetle growth rate was assessed as plants were infested with a single third-instar (late-stage). After 72 h of late-stage beetle infestation, beetle mass was measured. It was found that early-stage beetles inflicted more damage on AM+ tomatoes. Interestingly, this corresponds with fewer trichomes on AM+ tomatoes, as well as higher early-stage beetle survivorship. Specifically, AM taxon, C. claroideum increases herbivory and thereby reduces beetle mortality. Among late-stage beetles, C. claroideum does not improve beetle growth nor rate of survival. This suggests that AM taxa that are beneficial to early-stage beetles may not necessarily provide an advantage to late-stage beetles. Taken together, these findings highlight potential dependencies of AM-fungal effects on herbivory and herbivore life history, including growth and life-stage specific survival.
Chertkova EA, Grizanova EV, Dubovskiy IM. J Invertebr Pathol. 2018;153:203-206. doi: 10.1016/j.jip.2018.02.020.
Dopamine (DA) is known as a hormone neurotransmitter molecule involved in several stress reactions in both vertebrates and invertebrates. Following infections with the fungi Metarhizium robertsii or Beauveria bassiana and the bacterium Bacillus thuringiensis, dopamine the concentration was measured at different time points in the haemolymph of the Colorado potato beetle, Leptinotarsa decemlineata and the larvae of the greater wax moth Galleria mellonella. The infection with M. robertsii increased (4 to 12-fold) DA concentrations in the haemolymph of the potato beetle larvae and the oral infection by B. thuringiensis also lead to a 30 and 45-fold increase. During infection of the greater wax moth larvae with Beauveria bassiana and B. thuringiensis DA increased 4 to 20-fold and about 2 to 2,5-fold respectively, compared to non-infected insects. The relative DA concentrations varied between the two insects and depended on the pathogens and post infection time.
Wraight SP, Ramos ME. Biocontrol Sci Technol. 2017;27(3):348-363. doi: 10.1080/09583157.2017.1291904.
The effects of inoculation method on efficacy of two formulations of Beauveria bassiana strain GHA against Colorado potato beetle larvae were investigated. Under dry greenhouse conditions, ca. 58% mortality was observed among second-instar larvae exposed directly to sprays of B. bassiana conidia, whereas mortality among larvae exposed to similarly treated foliage (either leaf dorsal or ventral surfaces) was <10%. Mortality was ca. 64% among larvae exposed to both direct sprays and foliar spray deposits. Equivalent rates of mortality were observed among larvae treated with a clay-based wettable powder versus an emulsifiable oil-based formulation of B. bassiana conidia; however, this was observed despite application of an approximately 40% greater dose of WP-formulated conidia, indicating greater efficacy of the emulsifiable oil formulation. These results suggest that, under dry conditions, potato beetle larvae do not readily acquire an effective dose of conidia from treated foliage and that development of improved application technologies to more effectively target the larvae may ultimately prove more beneficial than development of formulations with greater foliar persistence.