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.

Field Ecology and Food Suitability of Tarsonemus spp. (Acari: Tarsonemidae).

Tarsonemus bakeri Ewing (Acari: Tarsonemidae) is a species of mite commonly associated with citrus in many countries including the United States. A short report in 1942 suggested this species is phytophagous, but it has not been reported as a pest in citrus or any other crop since then. A single survey of 78 orchards in three growing regions in California demonstrated that Tarsonemus spp. mites were only associated with leaf samples that had visible sooty mold. A seasonal population study in one citrus orchard showed that all life stages of Tarsonemus spp. were present year-round on leaves and fruit, with the population on fruit reaching a peak in December (59.7 ± 15.2 mites per fruit). Results from a food suitability study showed that the population declined sharply on both plastic and leaf substrate when the mites were not provided a supplementary food source. When supplementary food was provided in the form of Alternaria, honeydew, molasses, or combinations of these, mites survived and multiplied throughout the 29-d study, irrespective of the substrate. Tarsonemus bakeri were found on excised, decaying leaves collected from an orchard. These studies verify that Tarsonemus spp. are associated only with sooty mold in citrus orchards. T. bakeri populations cannot sustain themselves on leaf tissue alone, indicating that they are nondamaging to citrus and therefore need not be considered a phytosanitary concern by importing countries.

Food Suitability and Population Dynamics of Lorryia formosa (Acari: Tydeidae).

Lorryia formosa Cooreman (Acari: Tydeidae) is a species of mite commonly associated with citrus in many countries including the United States. A survey report in 1957 suggested phytophagous nature, while other studies claimed that L. formosa populations are associated with honeydew producing insects and sooty mold and it acts as a sanitizing agent. We investigated the effect of various diets on the survival and progeny production of L. formosa on excised leaves and the survival and potential to cause feeding damage to leaves of potted plants in a greenhouse study. A 2-yr field survey of a mandarin orchard was also conducted to elucidate the seasonal infestation, damage potential and population structure of L. formosa in a natural habitat. Results showed that all L. formosa adults and immatures died in less than 14 d on excised leaves, did not survive beyond 7 d on potted citrus plants alone, and caused no observable feeding damage to leaves or fruit. When sugar water, honeydew, or cottony cushion scale, Icerya purchasi Maskell (Hemiptera: Margarodidae), was present, adults and immatures survived the duration of the experiments and produced additional generations. The field survey showed that all stages of L. formosa were present in a mandarin orchard throughout the year and insecticide applications affected but did not eliminate mite populations. Fruit generally had a greater percentage infestation of mites (44.8 ± 4.0) than leaves (16.0 ± 4.7). These studies confirmed that L. formosa cannot sustain a population on leaf tissue alone and is nondamaging to citrus in California.

Temperature thresholds and degree-day model for Marmara gulosa (Lepidoptera: Gracillariidae).

The developmental thresholds for Marmara gulosa Guillén & Davis (Lepidoptera: Gracillariidae) were investigated in the laboratory by using 17, 21, 25, 29, and 33 degrees C. The lowest mortality occurred in cohorts exposed to 25 and 29 degrees C. Other temperatures caused >10% mortality primarily in egg and first and second instar sap-feeding larvae. Linear regression analysis approximated the lower developmental threshold at 12.2 degrees C. High mortality and slow developmental rate at 33 degrees C indicate the upper developmental threshold is near this temperature. The degree-day (DD) model indicated that a generation requires an accumulation of 322 DD for development from egg to adult emergence. Average daily temperatures in the San Joaquin Valley could produce up to seven generations of M. gulosa per year. Field studies documented two, five, and three overlapping generations of M. gulosa in walnuts (Juglans regia L.; Juglandaceae), pummelos (Citrus maxima (Burm.) Merr.; Rutaceae), and oranges (Citrus sinensis (L.) Osbeck; Rutaceae), for a total of seven observed peelminer generations. Degree-day units between generations averaged 375 DD for larvae infesting walnut twigs; however, availability of green wood probably affected timing of infestations. Degree-day units between larval generations averaged 322 for pummelos and 309 for oranges, confirming the laboratory estimation. First infestation of citrus occurred in June in pummelo fruit and August in orange fruit when fruit neared 60 mm in diameter. Fruit size and degree-day units could be used as management tools to more precisely time insecticide treatments to target the egg stage and prevent rind damage to citrus. Degree-day units also could be used to more precisely time natural enemy releases to target larval instars that are preferred for oviposition.

Influence of spray equipment and water volume on coverage of citrus and control of citricola scale, Coccus pseudomagnoliarum (Hemiptera: Coccidae) with mineral oil.

A trial was conducted in a commercial Citrus sinensis L. variety 'Washington' navel orange orchard to compare the coverage and efficacy against citricola scale Coccus pseudomagnoliarum (Kuwana) (Hemiptera: Coccidae) of 45.5 liters/ha of an nC24 agricultural mineral oil treatment applied by two different methods: a conventional air blast sprayer and a rotary atomizer. Three water volumes (2,340, 4,680, and 7,020 liters/ha) were applied with the air blast sprayer to determine the optimal spray volume for that equipment. A single volume (2,340 liters/ha) was applied with the rotary atomizer to compare its effectiveness with that of the air blast sprayer at this same volume. Results demonstrated that all treatments reduced citricola scale densities. Moreover, all treatments conducted with the air blast sprayer provided significantly greater coverage and significantly reduced citricola scale densities compared with the treatment made with the rotary atomizer. Larger water volume applications with the air blast sprayer did not significantly reduce citricola scale densities, although significantly better coverage was attained in the interior of the tree when spraying with 4,680 and 7,020 liters/ha. As a consequence, this study demonstrated that the increased coverage obtained by applying higher water volume with the air blast sprayer was not required for an optimal treatment in August, when the citricola scale population consisted of nymphs inhabiting the outside leaves of the tree.

Role of imidacloprid in integrated pest management of California citrus.

Portions of three commercial citrus orchards were treated for 1 yr with foliar imidacloprid or for 2 yr with a systemic formulation in a replicated plot design to determine the impact of this neonicotinoid on the San Joaquin Valley California citrus integrated pest management (IPM) program. Foliar-applied imidacloprid had little effect on California red scale, Aonidiella aurantii (Maskell); cottony cushion scale, Icerya purchasi Maskell; or citrus red mite, Panonychus citri (McGregor), populations. Short-term suppression of the parasitoids Aphytis melinus DeBach and Comperiella bifasciata Howard; vedalia, Rodolia cardinalis (Mulsant); and the predacious mite Euseius tularensis (Congdon) were observed. Suppression of natural enemies allowed scales and mites to maintain higher populations in the treated areas compared with the nontreated areas. Thus, foliar imidacloprid did not exhibit control of these citrus pest species, and it disrupted biological control. Systemically applied imidacloprid suppressed California red scale and citricola scale populations 2-3 mo after treatment. Suppression of parasitoids of the California red scale also was observed. Thus, treatments of systemic imidacloprid applied in areawide management programs for invasive pests would provide a benefit of California red scale and citricola scale suppression. However, this treatment provided only single-season control of citricola scale, it was somewhat disruptive of biological control, and it did not suppress densities of either scale as low as a treatment of the organophosphate chlorpyrifos for citricola scale or the insect growth regulator pyriproxyfen for California red scale. Insecticides with longer periods of efficacy and greater IPM compatibility than imidacloprid should be used for a sustainable IPM approach in California citrus.

Role of two insect growth regulators in integrated pest management of citrus scales.

Portions of two commercial citrus orchards were treated for two consecutive years with buprofezin or three consecutive years with pyriproxyfen in a replicated plot design to determine the long-term impact of these insect growth regulators (IGRs) on the San Joaquin Valley California integrated pest management program. Pyriproxyfen reduced the target pest, California red scale, Aonidiella aurantii Maskell, to nondetectable levels on leaf samples approximately 4 mo after treatment. Pyriproxyfen treatments reduced the California red scale parasitoid Aphytis melinus DeBach to a greater extent than the parasitoid Comperiella bifasciata Howard collected on sticky cards. Treatments of lemons Citrus limon (L.) Burm. f. infested with scale parasitized by A. melinus showed only 33% direct mortality of the parasitoid, suggesting the population reduction observed on sticky cards was due to low host density. Three years of pyriproxyfen treatments did not maintain citricola scale, Coccus pseudomagnoliarum (Kuwana), below the treatment threshold and cottony cushion scale, Icerya purchasi Maskell, was slowly but incompletely controlled. Buprofezin reduced California red scale to very low but detectable levels approximately 5 mo after treatment. Buprofezin treatments resulted in similar levels of reduction of the two parasitoids A. melinus and C. bifasciata collected on sticky cards. Treatments of lemons infested with scale parasitized by A. melinus showed only 7% mortality of the parasitoids, suggesting the population reduction observed on sticky cards was due to low host density. Citricola scale was not present in this orchard, and cottony cushion scale was slowly and incompletely controlled by buprofezin. These field plots demonstrated that IGRs can act as organophosphate insecticide replacements for California red scale control; however, their narrower spectrum of activity and disruption of coccinellid beetles can allow other scale species to attain primary pest status.