Associate Professor University of British Columbia, British Columbia, Canada
Abstract: A key driver of insect biodiversity loss is the widespread use of pesticides, especially in agricultural ecosystems. Extensive use of pesticides results in the loss of ecosystem services such as biological pest control and pollination, which agricultural production relies on. One way to support these services while conserving insect biodiversity is to plant floral strips alongside crops. Unfortunately, the impacts of these habitat enhancements are often assessed using indicators that are not necessarily relevant to growers. For example, one of the most common indicators used to measure biological control is predator abundance. However, increased predator abundance doesn’t always translate into reduced crop damage. Additionally, predator abundance as an indicator may not provide incentive for growers to implement more sustainable agricultural practices such as habitat enhancements. Our goal was to assess how effective floral strips are at supporting biological control and pollination by measuring herbivory (pest damage) and pollinator visitation, respectively. We planted white clover and sweet alyssum floral strips alongside pepper plants in experimental field plots that were placed at least 200 m apart. Sweet alyssum is known to attract a wide range of predators such as ground beetles while white clover attracts pollinators. Floral strips were planted in an intermixed pattern using a 2:1 white clover to sweet alyssum seedling density in treatment plots two months prior to transplanting peppers. Each treatment plot had three floral strips in. Control plots received no floral strips, but were irrigated, fertilized, and mulched at the same rate as treatment plots. There were eight plots in total, four treatment and four control. Pollinator visitation to plots was recorded weekly; ground beetle activity and herbivory were recorded biweekly using pitfall traps and visual estimates, respectively. All peppers were harvested in the last week of September, and pepper characteristics such as fresh weight, length and width were also recorded. We found that pepper plots with floral strips had higher ground beetle activity, lower herbivory, and higher pollinator visitation rates but no differences were detected in pepper weight, length, or width. Contrary to our expectation, pepper plants in control plots were taller and produced more peppers throughout the season, despite higher herbivory and lower pollinator visitation. We discuss the reasons for the differences and their implications for best management practices. We conclude that relevant ecosystem service indicators and agricultural outcomes should be used together to assess the effectiveness of agricultural management schemes to support ecosystem services.
