Arthropod density observations and measures of crop production in California citrus

Early studies and theory suggested that complex landscapes harboring remnants of natural land should support natural enemy populations and reduce pest buildup in adjacent crops, whereas landscapes interspersed with urban land often provide alternate host plants of crop pests, facilitating pest spillover and amplifying pest pressure. However, recent meta-analyses have demonstrated that both pest and beneficial agricultural arthropods respond inconsistently to surrounding landscapes. These meta-analyses relied on studies of one to two pests per crop across many different crop and landscape contexts, which limits inferences about how growers might design landscapes for effective control of a full suite of pests attacking a given crop. Here, we harnessed an ecoinformatics dataset from California Citrus to examine the effects of surrounding natural and urban land on the densities of a complete suite of seven major pest species (7,625 observations) and one beneficial predator (335 observations). We also explored landscape effects on pesticide use and fruit production. Despite restricting this analysis to data collected in the same region and cropping system, we found that arthropods still exhibited mixed responses to surrounding landscapes. Among the eight Citrus-associated arthropods surveyed, greater amounts of nearby natural land resulted in two outcomes beneficial for farmers (lower pest densities or fewer pesticide applications targeting that pest), three adverse outcomes, and three neutral outcomes. Similarly, greater amounts of urban land resulted in one beneficial outcome, three adverse outcomes, and four neutral outcomes for growers. Our economic analysis demonstrated no significant effects of either natural or urban land on total pesticide use or fruit quality, but reduced total fruit yield in Citrus groves with more nearby natural land. Taken altogether, our results do not demonstrate clear support for the retention of natural habitat or minimization of urban land near cropland solely for the purpose of enhancing conservation biocontrol. Nonetheless, the value of natural land extends far beyond its utility for conservation biocontrol, and agricultural landscapes must still be managed to strike a balance between crop production and the preservation of biodiversity and ecosystem function.