The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is the most important pest of citrus worldwide because it serves as a vector of "Candidatus Liberibacter" species (Alphaproteobacteria) that cause huanglongbing (citrus greening disease). All commercially cultivated citrus is susceptible and varieties tolerant to disease expression are not yet available. Onset of disease occurs following a long latent period after inoculation, and thus the pathogen can spread widely prior to detection. Detection of the pathogen in Brazil in 2004 and Florida in 2005 catalyzed a significant increase in research on D. citri biology. Chemical control is the primary management strategy currently employed, but recently documented decreases in susceptibility of D. citri to several insecticides illustrate the need for more sustainable tools. Herein, we discuss recent advances in the understanding of D. citri biology and behavior, pathogen transmission biology, biological control, and chemical control with respect to "Candidatus Liberibacter asiaticus." Our goal is to point toward integrated and biologically relevant management of this pathosystem.

The effects of insecticides used for California citrus pest management were evaluated using larval and adult stages of vedalia beetle, Rodolia cardinalis (Mulsant). This predatory beetle is essential for control of cottony cushion scale Icerya purchasi (Williston) (Homoptera: Margarodidae) in San Joaquin Valley citrus. When adult beetles were exposed to treated citrus leaves, adult survival was significantly reduced by the foliar neonicotinoid imidacloprid and the pyrethroid cyfluthrin. Progeny production was significantly reduced by imidacloprid, cyfluthrin, fenpropathrin, and buprofezin. Buprofezin, pyriproxifen, and foliar imidacloprid also significantly reduced successful development of larvae into the adult stage. When vedalia stages were fed insecticide-treated cottony cushion scale reared on Pittosporum tobira (Thunb.) Ait, toxic effects were more severe than contact toxicity alone. Adult beetle survival was most profoundly reduced by the pyrethroids and to a lesser extent the foliar neonicotinoids acetamiprid and imidacloprid. Progeny production and larval development to adulthood were reduced by all insecticides but were most severely affected by pyriproxifen and the pyrethroids. Systemically applied neonicotinoids were toxic to vedalia larvae feeding on cottony cushion scale that had ingested these insecticides. These data demonstrate that IGRs, neonicotinoid insecticides, and pyrethroid insecticides have a significant, negative impact on vedalia beetles. Depending on the rate of insecticide used, the number and timing of applications, and the level of coverage of the tree, disruption of vedalia can be minimized. However, the situation is made difficult when pests such as citrus thrips Scirtothrips citri (Moulton) (Thysanoptera: Thripidae), forktailed bush katydid Scuddaria furcata Brunner von Wattenwyl (Orthoptera: Tettigoiniidae), or glassy-winged sharpshooter Homalodisca coagulata Say (Homoptera: Cicadellidae) require these pesticide treatments during periods of vedalia beetle activity.

Crop plant compensation for herbivory and the population dynamics of herbivores are two key elements in defining an herbivore's pest status. We studied the dynamics of natural, unmanipulated populations of the aphid Aphis gossypii on seedling plantings of cotton, Gossypium hirsutum and Gossypium barbadense, over a 4-year period in California's Central Valley. Aphid populations colonized all plantings, but reached densities in excess of 0.5 aphids/leaf during only one year (1991), when outbreaks occurred. Outbreak populations were, however, ephemeral; predation and parasitism suppressed aphid populations prior to the initiation of flower bud production, when cotton plant growth may become photosynthate-limited. Effective natural biological control was observed despite the action of hyperparasitoids and the heavy mortality of immature parasitoids that occurred when predators consumed parasitized aphids.We conducted manipulative experiments during 1991 and 1992 to quantify the ability of pre-reproductive G. hirsutum to compensate for aphid herbivory. In 1991 aphid populations in the high-damage treatment reached densities as high as any observed naturally during the past 37 years. Damage symptoms were severe: leaf area was reduced by up to 58% and total above-ground plant biomass was reduced by 45%. By the time of crop harvest, however, plants had compensated fully for the early damage in each of the three traits that define cotton's economic value: the timing of crop maturation, the yield of cotton fiber, and the quality of cotton fiber. Aphid feeding damage did, however, produce some changes in plant architecture that persisted throughout the growing season, including a decrease in the number of vegetative branches. In 1992 aphid populations and associated damage were much lighter, but the qualitative responses to herbivory were consistent with those observed in 1991. Plant compensation for early damage was complete for economically significant measures, and vegetative branch production was again suppressed in mature cotton plants. There was no evidence for a change in the suitability of G. hirsutum as a host plant for A. gossypii as a result of early damage ('induced resistance').We conclude that pre-reproductive G. hirsutum, which has not yet begun strong allocations to reproductive structures or established architectural complexity, has retained effective means of compensating for herbivory. In contrast to other systems exhibiting strong compensation, G. hirsutum appears to compensate in part by enhancing apical dominance. The recognition of early-season A. gossypii as non-pests is critical to the sustainability of cotton production, because it will allow growers to forego pesticide applications that accelerate the evolution of pesticide-resistance and disrupt natural communities of predators and parasitoids.

Imidacloprid and its metabolites were detected in the nectar and pollen of citrus trees treated up to 232 days prior to the onset of bloom. However, based on published bioassay data, the imidacloprid concentrations in the floral nectar did not surpass levels that would compromise foraging activity under normal use conditions for imidacloprid. Further research is needed to assess the impact of elevated levels of imidacloprid within stored nectar in the comb.