Mating Disruption of the California Red Scale, Aonidiella aurantii (Hemiptera: Diaspididae) in Central California Citrus.

A warmer climate and the development of pesticide resistance have led to an increase in the number of generations and higher population densities of California red scale, Aonidella aurantii (Maskell) in central California. Commercial citrus orchard studies were conducted to determine how effective mating disruption using CheckMate CRS was at reducing A. aurantii. In 2016-2017, two replicated trials were conducted in 15.0-15.5 ha orchards and in 2018 and 2019, one half of each of 10 orchards 8-16.2 ha in size were treated with CheckMate CRS. Mating disruption significantly suppressed male captures for up to 8 mo. Average reductions of 90% in cumulative male flight trap catches were recorded, twig and leaf infestations were reduced by 95%, and highly scale-infested fruit were reduced by 75% in the CheckMate CRS plots for the 2018 and 2019 trials. In seven of 12 sites the percentage of highly infested fruit was reduced below 0.5%. Leaf and twig infestations in August and reductions in male captures during the 4th flight were strongly related to the percentage of highly infested fruit at the end of the season and could be used as predictors of the success of mating disruption. The results of the study indicated mating disruption using CheckMate CRS can be an effective method to reduce California red scale populations throughout the 4+ generations that occur in central California. Mating disruption has the potential to reduce or eliminate pesticide applications, especially in low scale density situations.

Impact of Insecticide Treatments for Phyllocnistis citrella (Lepidoptera: Gracillariidae) on Growth and Yield of Young Citrus reticulata Mandarins.

The citrus leafminer, Phyllocnistis citrella Stainton, is an invasive pest of citrus whose larvae damage developing leaves, which can impact tree photosynthetic capacity and may ultimately reduce tree growth and yield. Damage is most pronounced in young trees due to their greater propensity for production of new foliage, which supports P. citrella oviposition and larval development. We studied P. citrella damage and tree growth and yield among different insecticide treatment regimes to gauge their effectiveness at protecting young citrus trees. Three levels of insecticide treatments were applied over 3 yr to 'Tango' mandarin (Citrus reticulata Blanco) citrus trees planted in the prior summer, which were inspected regularly along with untreated trees. Leaves suitable for oviposition by P. citrella were available during all census dates, though their numbers fluctuated in the summer months. Phyllocnistis citrella were suppressed for 2-3 wk by systemic or foliar treatments of insecticides. The higher number of treatments provided more sustained suppression of larvae. Trunk diameter was unchanged and canopy volume affected by only the most aggressive treatment regime. However, citrus yield was 2-2.5 times higher following the second year of treatments and 1.2- to 1.8-fold times following the third year of treatments for trees in the treatment regimes that included systemic imidacloprid plus 2-3 or 4-5 foliar applications, respectively, relative to untreated controls. Suitable leaf flush and larval densities declined over the 3 yr of the study. These data support the use of insecticidal control of P. citrella to protect young 'Tango' mandarin trees, but demonstrated that frequent applications are necessary to suppress populations.

Is Vector Control Sufficient to Limit Pathogen Spread in Vineyards?

Vector control is widely viewed as an integral part of disease management. Yet epidemiological theory suggests that the effectiveness of control programs at limiting pathogen spread depends on a variety of intrinsic and extrinsic aspects of a pathosystem. Moreover, control programs rarely evaluate whether reductions in vector density or activity translate into reduced disease prevalence. In areas of California invaded by the glassy-winged sharpshooter (Homalodisca vitripennis Germar), Pierce's disease management relies heavily on chemical control of this vector, primarily via systemic conventional insecticides (i.e., imidacloprid). But, data are lacking that attribute reduced vector pressure and pathogen spread to sharpshooter control. We surveyed 34 vineyards over successive years to assess the epidemiological value of within-vineyard chemical control. The results showed that imidacloprid reduced vector pressure without clear nontarget effects or secondary pest outbreaks. Effects on disease prevalence were more nuanced. Treatment history over the preceding 5 yr affected disease prevalence, with significantly more diseased vines in untreated compared with regularly or intermittently treated vineyards. Yet, the change in disease prevalence between years was low, with no significant effects of insecticide treatment or vector abundance. Collectively, the results suggest that within-vineyard applications of imidacloprid can reduce pathogen spread, but with benefits that may take multiple seasons to become apparent. The relatively modest effect of vector control on disease prevalence in this system may be attributable in part to the currently low regional sharpshooter population densities stemming from area-wide control, without which the need for within-vineyard vector control would be more pronounced.

Invertebrate carcasses as a resource for competing Aedes albopictus and Aedes aegypti (Diptera: Culicidae).

Terrestrial invertebrate carcasses are an important resource for insects developing in pitcher plants. However, little is known of the role of these carcasses in other containers, which also receive leaf fall and stemflow inputs. This experiment investigated effects of accumulated invertebrate carcasses as a resource for two competing mosquitoes, Aedes albopictus (Skuse) and Aedes aegypti (L.), whether either species differentially benefited from accumulated carcasses, and if such a benefit affected interspecific competition. First, we measured accumulation of invertebrate carcasses in standard containers at a field site. We then used a replacement series with five different species ratios at the same total density, and varied the input of invertebrate carcasses [dead Drosophila melanogaster (Meigen) ] in three levels: none, the average input from our field site, or the maximum input recorded at our field site. Survivorship, development time, and mass were measured for each mosquito species as correlates of population growth, and were used to calculate a population performance index, lambda'. There were strong positive effects of invertebrate carcass additions on all growth correlates and lambda'. Differences in performance between species were pronounced in small or no carcass additions and absent in large inputs of invertebrate carcasses, but there was little evidence that inputs of invertebrate carcasses altered the competitive advantage in this system. These results suggest that terrestrial invertebrate carcasses may be an important resource for many types of container communities, and large accumulations of dead invertebrates may reduce resource competition between these mosquitoes, thus favoring coexistence. We propose that the total amount of resource, including accumulated invertebrate carcasses, may explain observed patterns of replacement involving these mosquitoes.