To enhance biological pest control in crop fields, it is recommended to increase semi‐natural area on farm and decrease insecticide spraying. While the benefits of semi‐natural area for biocontrol in unsprayed fields are often demonstrated, it remains largely unknown if there are any benefits in real‐world, commonly sprayed crops. Here, we explored the combined effects of semi‐natural field margins and insecticide spraying on pest (cotton bollworm) egg predation in 53 Australian cotton fields and semi‐natural field margins across 2 years. We used predation experiments close to field edges to exclude functional groups of predators depending on their spatio‐temporal activity (diurnal vs. nocturnal and ground vs. canopy dwelling) and digital cameras to record natural enemy taxa responsible for predation. Ground predation was substantially higher than canopy predation and its magnitude in unsprayed crops with semi‐natural margins was similar to that within semi‐natural areas. In contrast, semi‐natural field margins did not benefit biocontrol in sprayed crop fields and did not influence recovery rate of biocontrol after spraying. Within ground‐dwelling predators, one dominant taxon contributed the most to biocontrol at a particular time and place. However, the dominant predator–prey interactions changed between day and night and fields with and without margins, thus indicating increased importance of additional predator taxa with increasing spatio‐temporal scales. Synthesis and applications. Our results show that semi‐natural margins benefit pest control only in unsprayed fields. Spraying at different time (e.g. during night) would not reduce the negative effects of insecticides because it would affect complementary group of nocturnal natural enemies that exert equally high biocontrol as diurnal ground‐dwelling predators. We highlight the need for management recommendations to simultaneously consider pros and cons of within‐field spraying and surrounding semi‐natural habitats to maximize their benefits in high‐input conventional production systems.
1. Insect pollination and biological pest control simultaneously influence crop yield, but are often investigated individually. This can lead to under-or over-estimation of the importance of individual services when they interact to affect yield. Recent, limited evidence from field studies showed contrasting results with both additive and non-additive positive and negative effects.2. To disentangle the mechanisms underlying these responses, we conducted a greenhouse experiment and a field study. We tested the potential and realized contribution of insect pollination to cotton boll retention and yield under various pest pressures and biocontrol levels.3. We found both additive and interactive effects of insect pollination and biocontrol within a single crop system depending on the level of pest pressure. In the greenhouse experiment, pollination did not contribute to cotton boll retention and final yield at low pest pressure. At high pest abundances, boll retention and final yield were higher when pollinators were present. In the field study, pollination was sufficient to alter the negative effect of pests on boll retention. Thus, interactive effect between the two ecosystem services on boll retention was present at high pest pressure in the greenhouse and at natural levels of pest pressure in the field, but not at lower pest abundances in controlled conditions. 4. Although cotton plants partly compensated for bolls shedding by increasing their weight in the greenhouse experiment, this effect was not detected in the field study, likely due to higher environmental variation. Similarly, interactive effect of pollination and biocontrol on the final yield was present only in the greenhouse study. Synthesis and applications.We conclude that the contrasting findings of additive versus non-additive effects between ecosystem services may be due to the levels of services and disservices tested and environmental variation. Further, this study shows that even when an ecosystem service does not appear to limit crop yield, it can make a substantial contribution to yield and act as insurance when the other service is reduced. For achieving food and fibre security, it is essential that future studies test interactive effects between these ecosystem services in different systems and environmental conditions.
Bees are mobile organisms that seek food and nesting opportunities from a range of habitats. It is important to understand the way they move in agricultural landscapes if we are to conserve them and benefit from their activity as pollinators. We surveyed bees using directional flight interception (Malaise) traps over a 1-year period in two agricultural landscapes in south-east Queensland, Australia. We placed traps at the ecotone between crops and remnant vegetation to establish the pattern of movement between these habitats. Species richness in these landscapes (70) was high relative to that in comparable studies. Some bees were active year round, but most were caught in the period September to March. Across the whole assemblage there was a significant pattern where more species were detected leaving rather than entering remnant vegetation. The same bias was true for the number of individuals of the two most abundant species (Homalictus urbanus and Apis mellifera). Species exclusively found in crops were smaller on average (and therefore have smaller foraging range) than their non-crop counterparts. Together, these patterns indicate that while bees are abundant in crop habitat, the remnant vegetation is important as the point of origin for bee movements, and the riparian remnant in particular is richer than the dry native remnant. Compositional similarity among samples was significantly explained by landscape but also movement direction (i.e. to or from the riparian remnant) because different species showed different patterns of response.The landscape with greater native vegetation cover supported more species in and around crops than the landscape with less native vegetation.
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