Ecoinformatics Can Infer Causal Effects of Crop Variety on Insect Attack by Capitalizing on 'Pseudoexperiments' Created When Different Crop Varieties Are Interspersed: A Case Study in Almonds

Development of DNA Melt Curve Analysis for the Identification of Lepidopteran Pests in Almonds and Pistachios

Simple Summary

Almonds and pistachios are fed upon by a diverse assemblage of lepidopteran insects, several of which are economically important pests. Unfortunately, identification of these pests can be difficult, as specimens are frequently damaged during collection, occur in traps with non-target species, and are morphologically similar up to their third instar. Here, we present a quantitative PCR based melt curve analysis for simple, rapid, and accurate identification of six lepidopteran pests of almonds and pistachios: navel orangeworm, peach twig borer, oriental fruit moth, obliquebanded leafroller, raisin moth, and Indian meal moth. We demonstrate that the dissociation or the “melt” temperature(s) of a 658 bp section of cytochrome c oxidase subunit 1 provides unambiguous species level identification of these six species and is reproducible in field specimens collected following conventional orchard practices. The melt curve’s simplicity allows it to be performed in any basic molecular biology laboratory with a quantitative PCR.

Abstract

Almonds and pistachios are fed upon by a diverse assemblage of lepidopteran insects, several of which are economically important pests. Unfortunately, identification of these pests can be difficult, as specimens are frequently damaged during collection, occur in traps with non-target species, and are morphologically similar up to their third instar. Here, we present a quantitative PCR based melt curve analysis for simple, rapid, and accurate identification of six lepidopteran pests of almonds and pistachios: navel orangeworm (Amyelois transitella), peach twig borer (Anarsia lineatella), oriental fruit moth (Grapholita molesta), obliquebanded leafroller (Choristoneura rosaceana), raisin moth (Cadra figulilella), and Indian meal moth (Plodia interpunctella). In this approach, the dissociation (melt) temperature(s) of a 658 bp section of cytochrome c oxidase subunit 1 was determined using quantitative PCR (qPCR). Within these six species, the distribution and the number of melt peak temperatures provide an unambiguous species level identification that is reproducible when unsheared DNA can be extracted. The test is robust across a variety of sampling approaches including insects removed from sticky card traps, museum specimens, and samples that were left in the field for up to 7 days. The melt curve’s simplicity allows it to be performed in any basic molecular biology laboratory with a quantitative PCR.

Individual and Additive Effects of Insecticide and Mating Disruption in Integrated Management of Navel Orangeworm in Almonds

Simple Summary

Mating disruption is an increasingly important part of pest management for the navel orangeworm Amyelois transitella. Industry groups have long supported mating disruption research and development with the divergent objectives of both minimizing damage from this key pest and reducing insecticide used on these crops. It is therefore important to know whether the benefits of mating disruption and insecticide are additive or, alternatively, if using both together provides no additional benefit over either alone. Ten years of data from research trials in a large commercial almond orchard found that the benefits of mating disruption are generally additive with lower damage if both are used together than either alone. Substantial year-to-year variability in navel orangeworm damage was also evident, even with stringent management. These findings indicate that the combination of mating disruption and insecticide can reduce the impact of navel orangeworm damage on the almond industry. Further improvements in monitoring and predictions of navel orangeworm abundance and damage are necessary for mating disruption to effectively contribute to the industry goal of reduction of insecticide use by 25%.

Abstract

Damage from Amyelois transitella, a key pest of almonds in California, is managed by destruction of overwintering hosts, timely harvest, and insecticides. Mating disruption has been an increasingly frequent addition to these management tools. Efficacy of mating disruption for control of navel orangeworm damage has been demonstrated in experiments that included control plots not treated with either mating disruption or insecticide. However, the navel orangeworm flies much farther than many orchard pests, so large plots of an expensive crop are required for such research. A large almond orchard was subdivided into replicate blocks of 96 to 224 ha and used to compare harvest damage from navel orangeworm in almonds treated with both mating disruption and insecticide, or with either alone. Regression of navel orangeworm damage in researcher-collected harvest samples from the interior and center of management blocks on damage in huller samples found good correlation for both and supported previous assumptions that huller samples underreport navel orangeworm damage. Blocks treated with both mating disruption and insecticide had lower damage than those treated with either alone in 9 of the 10 years examined. Use of insecticide had a stronger impact than doubling the dispenser rate from 2.5 to 5 per ha, and long-term comparisons of relative navel orangeworm damage to earlier- and later-harvested varieties revealed greater variation than previously demonstrated. These findings are an economically important confirmation of trade-offs in economic management of this critical pest. Additional monitoring tools and research tactics will be necessary to fulfill the potential of mating disruption to reduce insecticide use for navel orangeworm.

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.

Optimizing Efficiency of Aerosol Mating Disruption for Navel Orangeworm (Lepidoptera: Pyralidae)

Improved cost efficiency for aerosol mating disruption for the navel orangeworm, Amyelois transitella Walker, was examined in experiments performed between 2015 and 2017. A programmable dispenser was used to explore the effects of frequency of treatment, time of night when pheromone was emitted, and the concentration of pheromone required. A negative curvilinear trend of males captured as a function of emission frequency was evident in the range of 2-12 emissions per hour. A subsequent experiment found greater trap suppression when the same amount of active ingredient was emitted seven times per hour compared with the same amount of material emitted at twice the concentration but half the frequency. Another experiment found no significant difference in cumulative trap suppression between treatment for the last 4 or 6 h of the night compared with 12 h. A subsequent experiment comparing a current commercial mating disruption system emitting for 12 h with a proposed alternative emitting more material per hour for fewer hours showed similar levels of suppression of males in pheromone traps. A season-long efficacy trial using dispensers deployed and programmed based on these findings demonstrated significant reduction of damage to Nonpareil almonds treated with mating disruption. These data reveal important information about the response of the navel orangeworm to aerosol mating disruption, which provides improved cost-effectiveness compared with the status quo ante. These findings for navel orangeworm are discussed in relation to studies of aerosol mating disruption for the codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae).