An exploratory analysis of the structure of tetranychid and phytoseiid assemblages in walnut orchards in California.

Spider mites were considered secondary pests of walnut production in California, under the control of phytoseiid predators. Due to increased importance as walnut pests in recent decades there is renewed interest in the structure and function of the associated phytoseiid assemblage. In this study we report the results from a 3 year survey of the tetranychid and phytoseiid assemblages in walnut orchards in the Central Valley of California. The survey was conducted to determine the range and dominance of web-spinning Tetranychus species present, to investigate the species richness and dominance of the phytoseiid species present, and to explore whether patterns of variation in the relative abundance of phytoseiid species could be explained by one or more explanatory variables. Tetranychus urticae was the dominant spider mite in all growing regions and years with T. pacificus and T. turkestani also present in orchards in the southern San Joaquin Valley. Phytoseiid species richness declined with latitude among the three walnut growing regions and of the 13 species found Amblyseius similoides, Euseius stipulatus, Galendromus occidentalis and Typhlodromus caudiglans were the most abundant and widespread species present. Mean proportional abundance significantly increased from early (mid May-July) to late (August-mid October) season and from southern to northern growing regions for Type II and IV predators, but significantly decreased from early to late season and from southern to northern growing regions for Type III predators. The mean proportional abundance of Type II predators, particularly G. occidentalis, significantly increased and that of Type III predators significantly decreased with mean Tetranychus density in individual orchards. The current survey provides a more in-depth analysis of mite assemblages in walnut orchards in California and can be used to better inform adaptive management strategies for integrated mite management in the future.

Impact of Citricola Scale Coccus pseudomagnoliarum (Hemiptera: Coccidae) on Valencia Orange, Citrus sinensis Production and Fruit Quality.

Citricola scale, [Coccus pseudomagnoliarum (Kuwana)], is a key pest of citrus requiring insecticide control in areas where biological control is ineffective. Here we quantified the relationship between C. pseudomagnoliarum density and Valencia orange (Citrus sinensis L. Osbeck) yield and sooty mold contamination to inform pest action thresholds. Two field experiments documented significant effects of adult or nymphal C. pseudomagnoliarum densities on fruit yield and sooty mold. Adults generally had more pronounced effects, reducing average tree yield by up to 43% and increasing sooty mold prevalence by at least 45%. Analyses estimated significant effects of C. pseudomagnoliarum at densities less than 0.1 adults/branch or 1.0 nymph/leaf. These results suggest a decrease in the current threshold of 1.0 for adults/branch and may be warranted to minimize C. pseudomagnoliarum damage.

Impact of Icerya purchasi (Hempitera: Monophlebidae) on Navel Orange, Citrus sinensis, Production and Fruit Quality.

Cottony cushion scale, Icerya purchasi Maskell, is an occasional pest of citrus, especially when insecticides disrupt vedalia beetle, Novius cardinalis (Mulsant) (Coleoptera: Coccinellidae). In two field tests conducted in successive years, navel orange trees were artificially infested with I. purchasi to determine the impact of I. purchasi on fruit yield and quality. In the first year, for which adult scale densities ranged between 0 and > 45 per branch and between 0 and > 500 on trunk counts, there was a highly significant negative linear relationship between the number of I. purchasi adults on branches or the trunk and its effect on fruit number, the percentage of large fruit, and the mass of fruit, and a highly significant positive relationship for the percentage of sooty mold-affected fruit and the percentage of juice grade fruit. In the second year, in which adult scale densities ranged between 0 and 10.5 per branch and between 0 and 35 on trunk counts, only the percentage of sooty mold-affected fruit showed a relationship. Damage to fruit was better predicted by population estimates from branch samples versus trunk counts. Analysis of the two years, estimated significant damage ranging from 2 adults per branch to no detectable effects of insect density, depending on the given metric of fruit number or quality, at the time that treatment decisions would be made. These results support May-June monitoring of branches for adult scales and application of treatments at an action threshold of <2 adult females/branch to prevent damage to navel orange trees.

Characterizing Herbivory by European Earwigs (Dermaptera: Forficulidae) on Navel Orange Fruit with Comparison to Forktailed Bush Katydid (Orthoptera: Tettigoniidae) Herbivory.

In establishing Integrated Pest Management (IPM) plans for understudied pests, it is crucial to understand the nature of their herbivory and resulting damage. European earwig (Forficula auricularia L.; Dermaptera: Forficulidae) densities are increasing in citrus orchards in Central California. Field observations suggest that earwigs feed on young, developing citrus fruit, but this hypothesis had not been examined with formal experimentation. Forktailed bush katydid nymphs (Scudderia furcata Brunner von Wattenwyl; Orthoptera: Tettigoniidae) are well-known citrus herbivores that feed on young citrus fruit, and it is possible that earwig damage may be misdiagnosed as katydid damage. Here we report findings from two field experiments in navel oranges (Citrus sinensis (L.) Osbeck; Sapindales: Rutaceae) that together tested: (1) whether earwigs damage young citrus fruit; (2) whether the amount of damage earwigs generate differs across developmental stage or sex of adult earwigs; (3) the window of time during which fruit are most sensitive to earwig damage; (4) whether damaged fruit are retained to harvest; and (5) the resulting damage morphology caused by earwigs relative to katydids. Earwigs, particularly nymphs, chewed deep holes in young citrus fruit from 0 to 3 wk after petal fall. Fruit damaged by earwigs were retained and exhibited scars at harvest. The morphology and distribution of scars on mature fruit only subtly differed between earwigs and katydids. This study establishes that earwigs can be direct pests in mature navel orange trees by generating scars on fruit and likely contribute to fruit quality downgrades.

Profile of Fork-Tailed Bush Katydid (Orthoptera: Tettigoniidae) Feeding on Fruit of Clementine Mandarins.

Sweet oranges (Citrus sinensis (L.) Osbeck Sapindales: Rutaceae) dominated commercial citrus production in California until recently when there has been a shift to mandarins, mostly Citrus reticulata (Blanco) mandarins and Citrus clementina (hort. ex Tanaka) clementines. Past analyses of commercial field scouting and harvest data indicated that fork-tailed bush katydids (Scudderia furcata Brunner von Wattenwyl), a major pest in oranges, are present in clementine groves, but that fruit scarring attributed to katydids is rare. Conversely, jagged or web-like scarring attributed to caterpillars was more prevalent than expected. We used two field experiments in four representative cultivars of clementines to test four explanatory hypotheses for this observation: 1) katydids do not feed on clementine fruit, 2) damaged clementine fruit recover, 3) damaged clementine fruit preferentially abscise, and 4) katydid scars on clementine fruit have a different, undocumented morphology, not recognized as katydid damage. We find support for the latter two hypotheses. Katydids fed readily on the clementine fruit of all cultivars tested, chewing irregular holes that developed into jagged or web-like scars of a range of shapes and often led to splitting and abscission of maturing fruit. The katydid scars often more closely resembled chewing caterpillar damage than the round katydid scars in oranges, suggesting that katydid damage is being misclassified in clementines. The resistance documented in some other mandarins was not observed. Katydids are clearly a frugivorous pest causing previously unrecognized scarring in clementines.

Arthropod Infestation Levels on Mandarins in California.

Integrated pest management (IPM) guidelines for horticulture are typically established from years of experimental research and experience for a crop species. Ecoinformatics methods can help to quickly adapt these guidelines following major changes in growing practices. Citrus production in California is facing several major challenges, one of which is a shift away from sweet oranges [Citrus sinensis (L.) Osbeck Sapindales: Rutaceae] toward mandarins (including mostly cultivars of C. reticulata Blanco and C. clementina hort. ex Tanaka). In the absence of IPM guidelines for mandarins, growers are relying on pest information developed from oranges. We mined a database of management records from commercial growers and consultants to determine densities for four arthropod pests: cottony cushion scale (Icerya purchasi Maskell Hemiptera: Monophlebidae), citricola scale (Coccus pseudomagnoliarum Kuwana Hemiptera: Coccidae), European earwig (Forficula auricularia Linnaeus Dermaptera: Forficulidae), citrus red mite (Panonychus citri McGregor Acari: Tetranychidae), and a natural enemy, predatory mites in the genus Euseius (Congdon Acarina: Phytoseiidae). Densities of cottony cushion scale were approximately 10-40 times higher in the two most commonly grown mandarin species than in sweet oranges, suggesting this pest is reaching outbreak levels more often on mandarins. Densities of the other pests and predatory mites did not differ significantly across citrus species. This is a first step toward establishing IPM guidelines for mandarins for these pests; more research is needed to determine how arthropod densities relate to crop performance in mandarins.

Resistance of Fruits From a Mandarin Cultivar to Feeding by Fork-Tailed Bush Katydids.

Plants use a variety of mechanisms to defend against herbivore damage, each with different consequences for agricultural production. Crops relying on tolerance strategies may need different pest management approaches versus those relying on resistance strategies. Previous work suggested that densities of fork-tailed bush katydids (Scudderia furcata Brunner von Wattenwyl [Orthoptera: Tettigoniidae]) that generated substantial scarring on cultivars of sweet oranges (Citrus sinensis, (L.) Osbeck [Sapindales: Rutaceae]) produced only low levels of scarring on cultivars of Citrus reticulata Blanco mandarins. We used field experiments in representative cultivars of these species to test non-mutually exclusive hypotheses regarding the mechanisms underlying this observation: 1) katydids are averse to feeding on mandarin fruits, 2) damaged mandarin fruits preferentially abscise, 3) damaged mandarin fruit tissue recovers during development, and 4) katydid scars on mandarins have a different morphology that may result in misclassification. We found strong support for the first hypothesis, demonstrating that katydids reject opportunities to feed on C. reticulata fruit. Instead of chewing deep holes in the fruit, as was commonly observed for C. sinensis, the katydids only scratched the surface of the C. reticulata fruits. The hypotheses of preferential abscission of damaged fruits and of recovery of damaged tissue were not supported. The low incidence of damage to the mandarins prevented a comprehensive assessment of the scar morphology; however, at harvest, the superficial cuts in C. reticulata were not easily distinguishable from background damage. This indicates that in contrast to C. sinensis, C. reticulata has substantial natural resistance to fork-tailed bush katydids making them a non-pest in this crop.

Differential Impacts of Citrus Thrips Across Sweet Orange and Mandarin Species.

Several domesticated Citrus species are grown as major commercial crops in California. Despite this, farmers currently use a single set of management practices, originally created for sweet oranges (Citrus sinensis (L.) Osbeck [Sapindales: Rutaceae]), for both sweet oranges and all mandarin species. Mandarins, primarily Citrus reticulata Blanco, Citrus clementina hort. ex Tanaka, and Citrus unshiu Marcovitch, comprise almost 25% of California citrus acreage, and little work has been done to assess host-pest interactions for these species. Citrus thrips (Scirtothripscitri Moulton [Thysanoptera: Thripidae]) are one of the main pests in California citrus and are major targets for early spring, "petal fall" insecticide applications. We used mixed species citrus blocks to test the influence of Citrus species, including C. sinensis, C. reticulata, C. clementina, and C. unshiu, on 1) citrus thrips densities following petal fall; 2) citrus thrips-induced scarring on both the calyx and stylar ends of fruit; and 3) fruit deformation. Citrus sinensis and C. unshiu had relatively high citrus thrips densities and scarring levels, whereas C. reticulata had lower densities of citrus thrips and scarring levels. The age structure of citrus thrips populations also varied across Citrus species. Fruit deformity associated with citrus thrips scarring was found on all Citrus species examined. Scarring on the stylar-end of fruit, a previously largely ignored location of citrus thrips scarring, was found to be common in C. reticulata. It is clear from our work that species-specific management guidelines for citrus thrips are needed in sweet oranges and mandarins.

Impacts of Fruit-Feeding Arthropod Pests on Oranges and Mandarins in California.

One of the major challenges facing citrus integrated pest management (IPM) in California is the recent, sharp increase in the acreage of mandarins being planted. The current citrus IPM guidelines have been established from years of experiments and experience in oranges, with no specific guidelines for mandarins. In the absence of research into key arthropod pest effects in mandarins, the assumption that the pest management practices for oranges appropriately transfer for optimal production in mandarins has not been tested. We used a data mining or 'ecoinformatics' approach in which we compiled and analyzed production records collected by growers and pest control advisors to gain an overview of direct pest densities and their relationships with fruit damage for 202 commercial groves, each surveyed for 1-10 yr in the main production region of California. Pest densities were different among four commonly grown species of citrus marketed as mandarins (Citrus reticulata, C. clementina, C. unshiu, and C. tangelo) compared with the standard Citrus sinensis sweet oranges, for fork-tailed bush katydids (Scudderia furcata Brunner von Wattenwyl [Orthoptera: Tettigoniidae]), and citrus thrips (Scirtothrips citri Moulton [Thysanoptera: Thripidae]). Citrus reticulata had notably low levels of fruit damage, suggesting they have natural resistance to direct pests, especially fork-tailed bush katydids. These results suggest that mandarin-specific research and recommendations would improve citrus IPM. More broadly, this is an example of how an ecoinformatics approach can serve as a complement to traditional experimental methods to raise new and unexpected hypotheses that expand our understanding of agricultural systems.

An Ecoinformatics Approach to Field-Scale Evaluation of Insecticide Effects in California Citrus: Are Citrus Thrips and Citrus Red Mite Induced Pests?

Experimental approaches to studying the consequences of pesticide use, including impacts on beneficial insects, are vital; however, they can be limited in scale and realism. We show that an ecoinformatics approach that leverages existing data on pesticides, pests, and beneficials across multiple fields can provide complementary insights. We do this using a multi-year dataset (2002-2013) on pesticide applications and density estimates of two pests, citrus thrips (Scirtothrips citri (Moulton [Thysanoptera: Thripidae])) and citrus red mites (Panonychus citri McGregor [Acari: Tetranychidae]), and a natural enemy (Euseius spp. predatory mites) collected from citrus groves in the San Joaquin Valley of California. Using correlative analyses, we investigated the long-term consequences of pesticide use on S. citri and P. citri population densities to evaluate the hypothesis that the pest status of these species is largely due to the disruption of natural biological control-i.e., these are induced pests. We also evaluated short-term pesticide efficacy (suppression of citrus thrips and citrus red mite populations immediately post-application) and asked if it was correlated with the suppression of Euseius predator populations. Although the short-term efficacy of different pesticides varied significantly, our dataset does not suggest that the use of citrus pesticides suppressed Euseius densities or worsened pest problems. We also find that there is no general trade-off between pesticide efficacy and pesticide risk to Eusieus, such that highly effective and minimally disruptive compounds were available to citrus growers during the studied time period.

Chemical Degradation of TMR Multilure Dispensers for Fruit Fly Detection Weathered Under California Climatic Conditions.

Degradation models for multilure fruit fly trap dispensers were analyzed to determine their potential for use in large California detection programs. Solid three-component male lure TMR (trimedlure [TML], methyl eugenol [ME], raspberry ketone [RK]) dispensers impregnated with DDVP (2, 2-dichlorovinyl dimethyl phosphate) insecticide placed inside Jackson traps were weathered during summer (8 wk) and winter (12 wk) in five citrus-growing areas. Additionally, TMR wafers without DDVP, but with an insecticidal strip, were compared to TMR dispensers with DDVP. Weathered dispensers were sampled weekly and chemically analyzed. Percent loss of TML, the male lure for Ceratitis capitata (Wiedemann) Mediterranean fruit fly; ME, the male lure for Bactrocera dorsalis (Hendel), oriental fruit fly; RK, the male lure for Bactrocera cucurbitae (Coquillett), melon fly; and DDVP was measured. Based on regression analyses for the male lures, TML degraded the fastest followed by ME. Degradation of the more chemically stable RK was discontinuous, did not fit a regression model, but followed similar seasonal patterns. There were few location differences for all three male lures and DDVP. Dispensers degraded faster during summer than winter. An asymptotic regression model provided a good fit for % loss (ME, TML, and DDVP) for summer data. Degradation of DDVP in TMR dispensers was similar to degradation of DDVP in insecticidal strips. Based on these chemical analyses and prior bioassay results with wild flies, TMR dispensers could potentially be used in place of three individual male lure traps, reducing costs of fruit fly survey programs. Use of an insecticidal tape would not require TMR dispensers without DDVP to be registered with US-EPA.

Spatiotemporal dynamics of the Southern California Asian citrus psyllid (Diaphorina citri) invasion.

Biological invasions are governed by spatial processes that tend to be distributed in non-random ways across landscapes. Characterizing the spatial and temporal heterogeneities of the introduction, establishment, and spread of non-native insect species is a key aspect of effectively managing their geographic expansion. The Asian citrus psyllid (Diaphorina citri), a vector of the bacterium associated with huanglongbing (HLB), poses a serious threat to commercial and residential citrus trees. In 2008, D. citri first began expanding northward from Mexico into parts of Southern California. Using georeferenced D. citri occurrence data from 2008-2014, we sought to better understand the extent of the geographic expansion of this invasive vector species. Our objectives were to: 1) describe the spatial and temporal distribution of D. citri in Southern California, 2) identify the locations of statistically significant D. citri hotspots, and 3) quantify the dynamics of anisotropic spread. We found clear evidence that the spatial and temporal distribution of D. citri in Southern California is non-random. Further, we identified the existence of statistically significant hotspots of D. citri occurrence and described the anisotropic dispersion across the Southern California landscape. For example, the dominant hotspot surrounding Los Angeles showed rapid and strongly asymmetric spread to the south and east. Our study demonstrates the feasibility of quantitative invasive insect risk assessment with the application of a spatial epidemiology framework.

Evaluation of systemic neonicotinoid insecticides for the management of the Asian citrus psyllid Diaphorina citri on containerized citrus.

BACKGROUND: Studies were conducted to evaluate uptake and retention of three systemic neonicotinoid insecticides, dinotefuran, imidacloprid and thiamethoxam, in potted citrus nursery plants treated at standard label rates. Infestation of these plants placed at a field site with moderate levels of Asian citrus psyllid (ACP) was monitored for 14 weeks following treatments, and insecticide residues in leaf tissue were quantified using enzyme-linked immunosorbent assay (ELISA). Bioassays were conducted using leaves harvested on various dates post-treatment to compare the efficacies of residues against adult ACP. RESULTS: Residues of the three neonicotinoids were detected in leaf tissues within 1 week after treatment. Peak concentrations established at 1 week for imidacloprid and dinotefuran and at 2 weeks for thiamethoxam. Imidacloprid and thiamethoxam outperformed the control and dinotefuran treatments at protecting trees from infestations by ACP eggs and nymphs. For a given insecticide concentration in leaf tissue, thiamethoxam induced the highest mortality of the three insecticides, and dinotefuran was the least toxic. CONCLUSION: If the time needed to achieve effective thresholds of a systemic neonicotinoid is known, treatments at production facilities could be scheduled that would minimize unnecessary post-treatment holding periods and ensure maximum retention of effective concentrations after the plants have shipped to retail outlets. The rapid uptake of the insecticides and retention at effective concentrations in containerized citrus suggest that the current 30 day post-treatment shipping restriction from production facilities to retail outlets outside of quarantine could be shortened to 14 days. Thiamethoxam should be added to the list of approved nursery treatments. © 2016 Society of Chemical Industry.

Captures of Wild Ceratitis capitata, Bactrocera dorsalis, and Bactrocera cucurbitae (Diptera: Tephritidae) in Traps with Improved Multilure TMR Dispensers Weathered in California.

During 2012­2013, solid Mallet TMR (trimedlure [TML], methyl eugenol [ME], raspberry ketone [RK]) wafers impregnated with DDVP (2, 2-dichlorovinyl dimethyl phosphate) insecticide were weathered during summer (8 wk) and winter (12 wk) in five California citrus-growing counties (Kern, Ventura, Orange, Tulare, and Riverside). In addition, TMR wafers without DDVP and with a Hercon Vaportape II insecticidal strip were compared with TMR dispensers with DDVP at Exeter and Riverside. Weathered treatments were shipped every week (overnight delivery) to Hawaii and frozen for a later bioassay in a 1,335-ha coffee plantation near Numila, Kauai Island, HI, where Mediterranean fruit fly, Ceratitis capitata (Wiedemann), oriental fruit fly, Bactrocera dorsalis Hendel, and melon fly, Bactrocera cucurbitae Coquillett, were all present. We compared trap captures of the three species, C. capitata, B. dorsalis, and B. cucurbitae, for the five different weathering locations. Captures of C. capitata, B. dorsalis, and B. cucurbitae with Mallet TMR dispensers (with DDVP) were not significantly different for the five locations. Captures with the Mallet TMR dispenser without DDVP and Vaportape were similar to those for Mallet TMR with DDVP, although there were some slight location differences. In conclusion, based on these results, the Mallet TMR dispenser could potentially be used in California habitats where large numbers of detection traps are currently deployed. Use of Vaportape with dispensers would not require them to be registered with US Environmental Protection Agency (EPA). Dispensers for use as Male Annihilation Technique (MAT) devices will be tested further in Hawaii.

Determination of exposure levels of honey bees foraging on flowers of mature citrus trees previously treated with imidacloprid.

BACKGROUND: Field and tunnel cage studies were undertaken to determine the extent to which honey bees foraging on citrus blossoms were exposed to imidacloprid and its metabolites when citrus trees were treated with soil applications of the insecticide. Residues were measured by LC/MS/MS in nectar and pollen samples from trees treated up to 232 days prior to bloom. RESULTS: Imidacloprid, imidacloprid olefin and 5-hydroxy imidacloprid were detected in nectar and pollen sampled from the flowers of citrus trees treated with imidacloprid up to 232 days prior to bloom. In tunnel studies, where foraging was restricted exclusively to citrus, imidacloprid residues in nectar extracted from flowers and from bee crops were similar (<10 ng mL(-1) ) and below the established no-observed-effects limit; however, the residue levels were about threefold higher in nectar sampled from comb. Concentrations of imidacloprid in nectar were higher in trees treated with higher application rates. CONCLUSIONS: 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.

Effects of spirotetramat on Aonidiella aurantii (Homoptera: Diaspididae) and its parasitoid, Aphytis melinus (Hymenoptera: Aphelinidae).

Laboratory and field studies were conducted to measure the effects of spirotetramat on life stages of California red scale, Aonidiella aurantii (Maskell), and a primary parasitoid, Aphytis melinus DeBach. Organophosphate-resistant and -susceptible populations responded similarly to spirotetramat, suggesting there is no cross-resistance between these insecticide classes. First and second instar male and female A. aurantii were 10- and 32-fold more susceptible to spirotetramat (LC50 = 0.1-0.2 ppm) compared with early third (LC50 = 1.5 ppm) and late third instar females (LC50 = 5.3 ppm). The LC99 value indicated that late stage third instar females would not be fully controlled by a field rate of spirotetramat; however, spirotetramat would reduce their fecundity by 89%. Field applications of spirotetramat in two water volumes and using two adjuvants (oil and a nonionic spray adjuvant) showed similar reduction in A. aurantii numbers, even though the higher water volume demonstrated more complete coverage. These data suggest that this foliarly applied systemic insecticide can be applied in as little as 2,340 liters/ha of water volume, minimizing application costs, and that the two adjuvants acted similarly. The endoparasitoid, A. melinus, was unaffected by the field rate of spirotetramat when it was applied to the host when the parasitoid was in the egg or larval stage. Adult A. melinus showed 2 wk of moderate reductions in survival when exposed to leaves with field-weathered residues. Spirotetramat is an integrated pest management compatible insecticide, effective in reducing A. aurantii stages and allowing survival of its primary parasitoid A. melinus.

Biology and management of Asian citrus psyllid, vector of the huanglongbing pathogens.

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.

Postharvest control of western flower thrips (Thysanoptera: Thripidae) and California red scale (Hemiptera: Diaspididae) with ethyl formate and its impact on citrus fruit quality.

The postharvest control of arthropod pests is a challenge that the California citrus industry must overcome when exporting fruit overseas. Currently, methyl bromide fumigation is used to control postharvest pests on exported citrus, but it may soon be unavailable because of use restrictions and cost of this health-hazard ozone-depleting chemical. Ethyl formate is a natural plant volatile and possible alternative to methyl bromide in postharvest insect control. The objectives of this study were 1) to evaluate the mortality of third instar California red scale [Aonidiella aurantii (Maskell)] (Hemiptera: Diaspididae) and adult western flower thrips [Frankliniella occidentalis (Pergande)] (Thysanoptera: Thripidae) under a wide range of ethyl formate concentrations, 2) to determine the ethyl formate concentration required to reach a Probit 9 level of control for both pests, and 3) to test the effects of ethyl formate fumigation on the quality of navel oranges [Citrus sinensis (L.) Osbeck] and lemons [Citrus limon (L.) Burman f.] at 24 h after fumigation, and at different time periods to simulate shipping plus storage (5 wk at 5 degrees C), and shipping, storage, handling, and shelf-life (5 wk at 5 degrees C, plus 5 d at 15 degrees C, and 2 d at 20 degrees C). The results indicate that ethyl formate is a promising alternative to methyl bromide for the California citrus industry, because of successful control of adult western flower thips and third instar California red scale and no deleterious effect on fruit quality at any of the evaluated periods and quality parameters.

Spirodiclofen and spirotetramat bioassays for monitoring resistance in citrus red mite, Panonychus citri (Acari: Tetranychidae).

BACKGROUND: Citrus red mite, Panonychus citri (McGregor), is a key pest of San Joaquin Valley California citrus. Spirodiclofen was registered for mite control in 2007, and spirotetramat for scale control in 2008. Because of the potential for resistance to spirodiclofen to develop in spider mites, and cross-resistance to spirotetramat used for other citrus pests, bioassay methods for resistance monitoring were developed. RESULTS: The responses of four populations of adult female, egg and larval stages of P. citri to spirodiclofen were compared to determine the most robust bioassay method for this pesticide. Adult females responded with a higher LC(99) and larval stages exhibited higher control mortality and a lower slope of response compared with the egg stage. Thus, the egg stage was found to be the most suitable stage for testing. Egg production and egg shape were significantly affected by spirodiclofen treatment of adult female mites. Bioassays with the related compound spirotetramat revealed that P. citri egg hatch was less affected by this compound, requiring the assessment of mortality to be extended to 11 days after treatment when the hatched larvae succumbed to the pesticide. Discriminating concentrations of 10 ppm for spirodiclofen and 31.6 ppm for spirotetramat in an 11 day bioassay were tested against eight field populations of P. citri, and 99-100% mortality resulted. CONCLUSION: These results provide a baseline for the response of P. citri to spirodiclofen and spirotetramat that will aid resistance management in California citrus.

Chlorpyrifos bioassay and resistance monitoring of San Joaquin Valley California citricola scale populations.

The responses to chlorpyrifos of six populations of citricola scale, Coccus pseudomagnoliarum (Kuwana) (Hemiptera: Coccidae), were tested using a leaf dip bioassay, and two- to nine-fold resistances were found. LC50 responses of nymphs ranged from 7.5 to 68.9 ppm and LC90 responses ranged from 20 to 222 ppm chlorpyrifos. A population tested monthly during August-October showed up to 3.5-fold differences in LC50 responses but no differences in LC90 responses as scale size increased. A diagnostic concentration of 178 ppm chlorpyrifos was used to test 93 populations from throughout the San Joaquin Valley California during 2006-2009 by using a leaf dip bioassay. Of the populations tested, 41% showed > 20% survival after exposure to the diagnostic concentration of chlorpyrifos, indicating resistance problems. Research is needed to relate the level of survival of the scales in the bioassay to the field efficacy of the insecticide. Tulare County citrus growers applied a higher number of organophosphate and carbamate insecticides during the 15-yr period from 1994 to 2008, and these orchards showed a higher average scale survival of chlorpyrifos and a higher number of locations with resistant scale compared with the other San Joaquin Valley counties. Chlorpyrifos resistance is a significant issue for citricola scale management because biological control is ineffective in the San Joaquin Valley and the alternative neonicotinoid and insect growth regulator (IGR) insecticides require more frequent application.