Recent advances in biological control of citrus pests and diseases

Abstract

Citrus cultivation is characterized by high species richness and an abundance of pest insects and associated natural enemies. Since the successful introduction of Novius (= Rodolia) cardinalis into California in the late 19th century, which resulted in the world’s first classical biological control (BC) program that targeted Icyerya purchasi, numerous classical BC programs have been initiated for the control of citrus pests, many of which have been very successful. The introduced and established new natural enemy species, together with the resident (both native and self-introduced), have enabled the development of conservation and augmentative BC programs in citrus. As a result, relatively few phytophagous species in citrus are considered key pests. However, this scenario has been disrupted by the spread of the lethal citrus disease, huanglongbing (HLB), caused by several bacteria of the genus Candidatus Liberibacter and vectored by psyllids, and by the higher arrival frequency of invasive pest species. Current management of HLB often requires broad-spectrum insecticide treatments to reduce vector densities to slow pathogen dissemination. Increased insecticide use in citrus disrupts BC and destabilizes Integrated Pest Management programs, which become more insecticide-intensive. The accelerating problem with invasive citrus pests is driven by increasing levels of international trade, tourism, and agriculture, as well as climate change. BC of these invasive pests in citrus is further complicated by increasing legal limitations imposed on the introduction of exotic natural enemies which further jeopardizes citrus farming in many citrus-producing regions. This special issue covers different aspects of BC programs against pests and diseases in several different citrus-growing regions. Work covered here also includes recent advances in BC postharvest citrus diseases and nematodes.