Long-term effects of management intensity and bioclimatic variables on leatherjacket (Tipula paludosa Meigen) populations at farm scale

Leatherjackets (Tipula spp.) are soil-dwelling pests associated with agriculture. Land management decisions made at farm scale can have subsequent effects on their populations. Between 1980 and 2020, surveys were conducted across Scotland to collect field histories and larval population data from grassland farms. To assess the impact of management and bioclimatic factors on leatherjacket occurrence over time, this study investigated data from fields continuously sampled between 2009 and 2018. We utilized a Generalized Linear Mixed-Effect Model on a dataset of 61 fields on 19 farms. Results indicated three significant factors affecting larval populations; field size, grazing type and application of insecticides or herbicides (referred to collectively as pesticides). Larval populations were significantly lower in fields that were larger in size and under sheep grazing, compared to no grazing. Pesticide application also caused a significant reduction in larval populations. Management variables were amalgamated to create a Management Intensity Index, revealing significantly increased larval populations under low-management systems. These results, coupled with significant effects of bioclimatic variables, pinpoint predictive signals for high infestations and potential routes for control strategies.