Does urbanization explain differences in interactions between an insect herbivore and its natural enemies and mutualists?

Urbanization can alter the composition of arthropod communities. However, little is known about how urbanization affects ecological interactions. Using experimental colonies of the black bean aphid Aphis fabae Scopoli reared on Vicia faba L, we asked if patterns of predator-prey, host-parasitoid and ant-aphid mutualisms varied along an urbanization gradient across a large town in southern England. We recorded the presence of naturally occurring predators, parasitoid wasps and mutualistic ants together with aphid abundance. We examined how biotic (green areas and plant richness) and abiotic features (impervious surfaces and distance to town center) affected (1) aphid colony size, (2) the likelihood of finding predators, mutualistic ants and aphid mummies (indicating the presence of parasitoids), and (3) how the interplay among these factors affected patterns of parasitoid attack, predator abundance, mutualistic interactions and aphid abundance. The best model to predict aphid abundance was the number of mutualistic ants attending the colonies. Aphid predators responded negatively to both the proportion of impervious surfaces and to the number of mutualistic ants farming the colonies, and positively to aphid population size, whereas parasitized aphids were found in colonies with higher numbers of aphids and ants. The number of mutualistic ants attending was positively associated with aphid colony size and negatively with the number of aphid predators. Our findings suggest that for insect-natural enemy interactions, urbanization may affect some groups, while not influencing others, and that local effects (mutualists, host plant presence) will also be key determinants of how urban ecological communities are formed

Numerical Modeling and Study of Vaporization of Single Droplet and Mono-dispersed Spray Under Mixed Convection Conditions

An approach to account for combined convection during droplet evaporation and study of pure component droplets and mono-dispersed sprays is presented. The classical gas-phase and infinite conductivity liquid-phase model are extended, with the use of an effective Reynolds number, to conflate the combined effects of forced and natural convection. The current model, after validation with experimental and numerical data using an independent code, is incorporated into a commercial CFD software, ANSYS Fluent, via user-defined functions with the Eulerian–Lagrangian numerical scheme. A validation study is carried out by comparing with available experimental, numerical, and analytical data on pure component droplets and a mono-dispersed spray, respectively, for without and with droplet dynamics. The results are shown in terms of mass fraction, droplet velocity, droplet diameter square, and droplet temperature. The validation shows reasonably good match between the present numerical data and experimental and analytical data, respectively, for initial Red/Grd 0.09, 2.12, and 60 evaporating droplets/sprays. It is concluded that the biofuels, for example, ethanol with a lower latent heat of vaporization, burn much like mono-component droplets and the blowing effect can be important in their modeling in the spray combustion