Management of ecosystems alters vector dynamics and haemosporidian infections

Abstract

The presence of insect vectors is a key prerequisite for transmission of vector-borne disease such as avian haemosporidians. In general, the effects of land use change on Diptera vectors are not well studied; the response of vectors to forest management depends on vector species, as has been shown previously for the birds. We tested if abundance of insects from different Diptera families and haemosporidian infection are affected through alteration of habitat structural variables (measured by LiDAR) and forest management intensities. We identified higher large-scale variation of female insect abundance in northeastern than in southwestern Germany. Unmanaged forest stands had higher Diptera insect abundances. We found that abundance of female Diptera increased with the amount of forest gaps but decreased in forest plots with more south facing aspect, higher habitat structural heterogeneity, temperature and humidity. We found that haemosporidian infections in Diptera insects increased with increased management intensity and more canopy structural diversity (e.g., amount of edge habitat), but decreased with a denser shrub layer, deeper leaf litter and higher humidity (characteristics for unmanaged forest stands). Although higher forest management intensity decreased vector abundance, the haemosporidian infections in the vectors increased, indicating a significant effect of forest management on disease dynamics.

Effects of forest structure on the interaction between avian hosts, dipteran vectors and haemosporidian parasites

“…Other studies have shown that land use management influences all components of the host-vector-parasite system: avian hosts [ 12 ], vector abundance (e.g. [ 28 ]), and parasite prevalence [ 20 ]. Our study confirms some parts of previous research but adding new insights and confirm that even subtle changes in forest structure, can have significant effects on host-vector-parasite interactions.…”

“…Insects were placed in a freezer at − 20 °C before immersion in 80% analytical grade ethanol. Insects were classified to the family level [59] and sorted to sex by morphology using a stereo microscope, species were determined by PCR and sequencing [20,60]. Vector abundance was calculated as the sum of all female individuals per forest plot for the families Culicidae, Ceratopogonidae, and Simuliidae that respectively transmit avian haemosporidians of the genera Plasmodium, Haemoproteus and Leucocytozoon [21].…”

“…The life history and habitat preferences of the avian hosts play an essential role in determining the likelihood of an infection [6,18]. Hence, habitat change alters ecosystem processes and species interactions, leading for example to higher infection rates in more intensively used habitats [19,20].…”

“…[27]). Similarly to the avian hosts, vectors may be affected by structural differences in forest habitats or forest management [20]. This ultimately affects vector distribution and abundance, subsequently influencing exposure to parasites and transmission risk [28,29], changing the spatial variation of prevalence in hosts [30].…”

“…Second, because vectors are known to be affected by forest habitat structure [20], we explicitly add dipteran vectors as an important mechanistic driver for the variation and spread of avian haemosporidians [28,33]. Based on the importance of vector abundance for the transmission of avian haemosporidians [27], we finally hypothesize that the amended models would better explain the host-vector-parasite interactions, compared to the previous study in which the models only included bird hosts and forest structure [19].…”