Upper thermal limits of Rhagoletis indifferens (Diptera: Tephritidae) pupae and pteromalid parasitoids (Hymenoptera: Pteromalidae) inside fly puparia.

Determining upper thermal limits of tephritid fly pupae can have practical implications for disinfesting soils and for predicting differential impacts of global warming on flies and their parasites. Here, upper thermal limits of Rhagoletis indifferens Curran (Diptera: Tephritidae) pupae and pteromalid wasps (Hymenoptera: Pteromalidae) inside puparia were determined. Puparia receiving sufficient chill to terminate pupal diapause were exposed to temperatures ramped linearly over 6 h from 21 °C to 47.8, 49.4, 51.1, 55.0, or 60.0 °C for a 0-h hold time. Flies eclosed when pupae were exposed to 47.8 °C but not to 49.4, 51.1, 55.0, or 60.0 °C nor in a separate test to 47.8 °C for 1-3 h hold times. All fly pupae in treatments where no eclosion occurred were dead based on puparial dissections. In contrast, adult wasps eclosed when puparia were exposed to 49.4 and 51.1 °C for 0 h and to 47.8 °C for 1- and 2-h hold times. Despite the greater upper thermal limits of wasps, heat delayed eclosion times of both adult flies and wasps, in 47.8 and 51.1 °C treatments, respectively. In separate tests, longevity of flies exposed as pupae to 47.3-48.6 °C was greater than of control flies, while longevity of control wasps and wasps exposed as immatures to 47.8-51.1 °C did not differ. Flies exposed as pupae to 47.2-48.6 °C produced as many eggs and puparia as control flies. Results suggest heat could be used to disinfest soils of puparia while sparing parasitoids. In addition, extreme heat waves due to global warming might be more detrimental to fly pupae than immature wasps.

Evidence for adaptation of Rhagoletis pomonella (Diptera: Tephritidae) on large-thorn hawthorn, Crataegus macracantha, in Okanogan County, Washington State, USA.

The apple maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), was introduced from eastern North America into western North America via infested apples (Malus domestica Borkhausen) about 44 yr ago, where it subsequently adapted to 2 hawthorn species, Crataegus douglasii Lindley and C. monogyna Jacquin. Here, we test whether R. pomonella has also adapted to large-thorn hawthorn, Crataegus macracantha Loddiges ex Loudon, in Okanogan County, Washington State, USA. In 2020, 2021, and 2022, fruit of C. macracantha were shown to ripen in late September and were infested at rates from 0.7% to 3.0%. In laboratory rearing studies, large-thorn hawthorn flies from C. macracantha eclosed on average 9-19 days later than apple flies from earlier ripening apple (August-early September), consistent with large-thorn hawthorn flies having adapted to the later fruiting phenology of its host. In a laboratory no-choice test, significantly fewer (64.8%) large-thorn hawthorn than apple flies visited apples. In choice tests, greater percentages of large-thorn hawthorn than apple flies resided on and oviposited into C. macracantha versus apple fruit. Large-thorn hawthorn flies were also smaller in size than apple flies. Our results provide further support for the recursive adaptation hypothesis that R. pomonella has rapidly and independently specialized phenologically and behaviorally to different novel hawthorn hosts since its introduction into the Pacific Northwest of the USA, potentially leading to host race formation.

Evaluation of Organic, Food-Grade Hydrophobic Coatings for Suppressing Oviposition and Increasing Mortality of Western Cherry Fruit Fly (Diptera: Tephritidae).

Newer organic options for protecting fruit from tephritid fruit fly attack are needed to reduce extensive insecticide use. Here, we evaluated organic, food-grade hydrophobic coatings that help protect sweet cherries (Prunus avium L.) from water-induced cracking for suppressing attack on cherries by western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephtitidae), as well as for their effects on fly mortality. Three formulations of coatings called HydroShield 13.20, 13.22, and 13.28 that form invisible elastic barriers on cherries and that consist of complex carbohydrates, fatty acids and occlusive agents, solvents, emulsifiers, emollients, surfactants, and other ingredients were tested. In the laboratory, fly visits on and oviposition in HydroShield-coated cherries were 66.1-92.8% and 59.1-99.5% lower, respectively, than in controls. The mean number of dead female flies exposed to HydroShield-coated cherries was 69.4-94.6% greater than of females exposed to control cherries. In the field, three sprays of HydroShield 13.22 and 13.20 on sweet cherry trees in 2020, when fly densities were high, reduced larval infestations in cherries by 32.1% and 31.8%, respectively. In the field in 2021, when fly densities were lower, three sprays of HydroShield 13.22 and 13.28 reduced infestations in cherries by 90.5% and 86.8%, respectively, but sprays also reduced cherry size and toughened cherries. HydroShield formulations show promise in protecting sweet cherry from attack by R. indifferens, but further testing is needed to improve formulations so that they suppress fly oviposition without affecting cherry quality.

Sensitivities to Chill Durations and No-Chill Temperatures Regulating Eclosion Responses Differ Between Rhagoletis zephyria (Diptera: Tephritidae) and its Braconid Parasitoids (Hymenoptera: Braconidae).

Seasonal temperatures select for eclosion timing of temperate insects and their parasitoids. In western North America, the fruit fly Rhagoletis zephyria Snow (Diptera: Tephritidae) is parasitized by the hymenopterous wasps Utetes lectoides (Gahan), an egg parasite, and Opius downesi Gahan, a larval parasite (both Braconidae). Eclosion of wasps should be timed with the presence of susceptible fly stages, but reports indicate U. lectoides ecloses in the absence of flies under no-chill conditions. Based on this, we tested the hypotheses that chill durations and no-chill temperatures both differentially regulate eclosion times of R. zephyria and its parasitic wasps. When fly puparia were chilled at ~3°C for 130-180 d, U. lectoides and O. downesi always eclosed on average later than flies. However, after 180-d chill, flies eclosed on average earlier than after 130- and 150-d chill, whereas eclosion times of U. lectoides and O. downesi were less or not affected by chill duration. When fly puparia were exposed to 20-22°C (no chill), U. lectoides eclosed before flies, with 88.9% of U. lectoides versus only 0.61% of flies eclosing. Taken together, findings show that eclosion times of flies are more sensitive to changes in chill duration than those of wasps. Flies are less sensitive than wasps to no-chill in that most flies do not respond by eclosing after no-chill while most wasps do. Our results suggest that shorter winters and longer summers due to climate change could cause mismatches in eclosion times of flies and wasps, with potentially significant evolutionary consequences.

Heat Treatments for Killing Apple Maggot Fly (Diptera: Tephritidae) Puparia for Application in Disinfesting Organic Yard Waste.

Organic yard waste from western Washington, U.S. that may contain puparia of apple maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), had been moved to central Washington for composting, threatening the $3 billion apple industry concentrated in that region. Heating waste to kill fly puparia before it is transported could be a solution to this problem. Here, we report results of studies in 2016-2021 that sought to identify a minimum heat treatment simulating that obtained using a low-pressure steam generator for maximizing kill of R. pomonella puparia. In two experiments, puparia were exposed to temperatures ramped linearly over 6 h from 21°C to 47.8, 51.1, 55.0, or 60.0°C in an oven. The 47.8, 51.1, and 55°C treatments did not achieve 100% mortality, although only one adult fly from 4,000 puparia was found in the 55°C treatment, while no puparia survived the 60°C treatment. In a third, similar experiment, no puparia out of 2,400 exposed to 55°C survived. In a fourth and final experiment conducted over 3 years, no puparia out of 61,223 exposed to a 6-h ramp from 21°C to 55°C followed by a 1-h hold time at 55°C produced flies. In addition, all puparia in this treatment died. Based on 42.3 to 69.8% control survival, 31,217 puparia were killed by this treatment with no survivors, for a probit 8.7190 level of security. Results suggest that the 55°C and 1-h hold time treatment here is close to the minimum heat regime needed for disinfesting organic waste of R. pomonella puparia.

Testing the potential contribution of Wolbachia to speciation when cytoplasmic incompatibility becomes associated with host-related reproductive isolation.

Endosymbiont-induced cytoplasmic incompatibility (CI) may play an important role in arthropod speciation. However, whether CI consistently becomes associated or coupled with other host-related forms of reproductive isolation (RI) to impede the transfer of endosymbionts between hybridizing populations and further the divergence process remains an open question. Here, we show that varying degrees of pre- and postmating RI exist among allopatric populations of two interbreeding cherry-infesting tephritid fruit flies (Rhagoletis cingulata and R. indifferens) across North America. These flies display allochronic and sexual isolation among populations, as well as unidirectional reductions in egg hatch in hybrid crosses involving southwestern USA males. All populations are infected by a Wolbachia strain, wCin2, whereas a second strain, wCin3, only co-infects flies from the southwest USA and Mexico. Strain wCin3 is associated with a unique mitochondrial DNA haplotype and unidirectional postmating RI, implicating the strain as the cause of CI. When coupled with nonendosymbiont RI barriers, we estimate the strength of CI associated with wCin3 would not prevent the strain from introgressing from infected southwestern to uninfected populations elsewhere in the USA if populations were to come into secondary contact and hybridize. In contrast, cytoplasmic-nuclear coupling may impede the transfer of wCin3 if Mexican and USA populations were to come into contact. We discuss our results in the context of the general paucity of examples demonstrating stable Wolbachia hybrid zones and whether the spread of Wolbachia among taxa can be constrained in natural hybrid zones long enough for the endosymbiont to participate in speciation.

Metabolic reserves of diapausing western cherry fruit fly (Diptera: Tephritidae) pupae in relation to chill duration and post-chill rearing conditions.

How different macronutrients are utilized at various stages of pupal diapause and the effects of winter length on nutrient reserves remain poorly studied for most insects. Western cherry fruit fly, Rhagoletis indifferens (Diptera: Tephritidae), is a specialist on cherries in higher latitudes or elevations in western North America that exhibits a obligate pupal diapause requiring chilling before adult development can occur. We determined the relationship between metabolic reserves and diapause status in R. indifferens pupae, testing the hypotheses that lipids are the primary reserves utilized during diapause and that long periods of warmth deplete these reserves more than periods of cold. Effects of 0- to 20-week durations at 3°C and subsequent exposure to 23°C and 16:8 L:D (warm rearing conditions) for 0 to 7 weeks on lipid, protein, soluble carbohydrates, and glycogen reserves of R. indifferens pupae were determined. During diapause, lipid reserves were the primary source of energy utilized by R. indifferens, while protein and soluble carbohydrates levels were stable throughout diapause and thus less utilized. At post-diapause, glycogen levels fluctuated the most, indicating that lipid reserves were utilized to produce glycogen to support metabolism for adult fly development. Unchilled pupae did not deplete lipid reserves, unlike chilled pupae, likely because unchilled pupae remained in diapause. Rhagoletis indifferens may have evolved a nutrient utilization strategy typical of rigid diapausing insects in higher latitude environments.

Tolerances of Apple Maggot (Diptera: Tephritidae) Larvae and Different Age Puparia to Water Flotation and Immersion.

Tolerance of terrestrial insects in temperate regions to water immersion and hypoxia has rarely been studied but can be an important adaptation to moist environments, with implications for insect dispersal through waterways. In the Pacific Northwest of the United States, apple maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), can be found in riparian habitats subject to flooding. Here, survival of R. pomonella larvae and different age puparia after flotation or immersion in 13.3°C or 21.1°C water for 1-12 d was determined. Larvae sank in water and when submerged for 1 or 2 d suffered greater mortality than control larvae. Fewer young (1-2 d old) than older puparia (13-15 d old) floated in water. When immersed in water for 1-12 d, young puparia suffered greater mortality than older puparia, which were not affected by water immersion. Consequently, fewer adult flies eclosed from puparia that had been water treated when young than older. Adult flies from pre-chill and post-chill puparia that had been water treated eclosed later than control flies, but treatment flies survived about 60 d and reproduced. Although newly-formed puparia are susceptible to hypoxic water conditions, increased buoyancy and water tolerance occur rapidly after formation, perhaps making survival possible and allowing water-borne dispersal of older puparia.

Contrast in Post-Chill Eclosion Time Strategies Between Two Specialist Braconid Wasps (Hymenoptera: Braconidae) Attacking Rhagoletis Flies (Diptera: Tephritidae) in Western North America.

Parasitoids comprise a speciose insect group, displaying a wide array of life history strategies. In the Pacific Northwest of the United States, the tephritid fruit flies Rhagoletis tabellaria (Fitch) and Rhagoletis indifferens Curran infest red osier dogwood, Cornus sericea L. (Cornaceae), and bitter cherry, Prunus emarginata (Douglas ex Hooker) Eaton (Rosaceae), respectively. The flies are parasitized by different braconid wasps at different life stages; Utetes tabellariae (Fischer) oviposits into R. tabellaria eggs, whereas Diachasma muliebre (Muesebeck) oviposits into R. indifferens larvae feeding in cherries. Because Rhagoletis only have one major generation a year and the wasps attack temporally distinct fly life stages, we predicted that eclosion times of U. tabellariae should more closely follow that of its host than the larval-attacking D. muliebre. As predicted, U. tabellariae eclosed on average 6.0-12.5 d later than R. tabellaria, whereas D. muliebre eclosed on average 32.1 d after R. indifferens. Unexpectedly, however, longer chill duration differentially affected the systems; longer overwinters minimally influenced eclosion times of R. tabellaria and U. tabellariae but caused earlier eclosion of both R. indifferens and D. muliebre. Results imply that in temperate regions, diapause timing in braconid wasps evolves in response to both host life stage attacked and fly eclosion characteristics, possibly reflecting differential effects of winter on host plant fruiting phenology. Differences in phenological sensitivity of the lower host plant trophic level to variation in environmental conditions may have cascading effects, sequentially and differentially affecting eclosion times in higher frugivore (fly) and parasitoid (wasp) trophic levels.

The Eclosion of Rhagoletis pomonella (Diptera: Tephritidae) Under Different Chill Durations and Simulated Temperate and Tropical Conditions.

The apple maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), is a serious pest of apple in North America that is subject to quarantine measures to prevent its spread to currently pest-free regions, including the tropics. How the fly may survive in warmer climates is unclear. Here, we studied the effects of exposing postchill puparia to simulated temperate and tropical environmental conditions on eclosion of R. pomonella from Washington State, U.S.A. Puparia were chilled for 0-30 wk at 3°C and then held under four postchill conditions: A = 23°C, 16:8 L:D, 40% RH; B = 26°C, 12:12 L:D, 80% RH; C = 26°C, 16:8 L:D, 80% RH; and D = 23°C, 12:12 L:D, 40% RH, with B and D representing tropical conditions and A and C temperate conditions. Within each chill duration, total numbers of flies eclosed were equally high in tropical treatment B and temperate treatment C, while they were lower in treatments A and D. Mean weeks of the first eclosion in treatments B and C were earlier than in treatment D; mean week of peak eclosion and 50% eclosion in treatments A, B, and C were earlier than in treatment D. Eclosion spans in treatments A, B, and D were generally shorter than in treatment C. Results suggest that if introduced into a humid tropical country, R. pomonella puparia from Washington State could produce adult flies, regardless of chill duration or lack of chilling during the pupal stage, but whether flies could establish there would require further study.

Distinct Adult Eclosion Traits of Sibling Species Rhagoletis pomonella and Rhagoletis zephyria (Diptera: Tephritidae) Under Laboratory Conditions.

Closely related phytophagous insects that specialize on different host plants may have divergent responses to environmental factors. Rhagoletis pomonella (Walsh) and Rhagoletis zephyria Snow (Diptera: Tephritidae) are sibling, sympatric fly species found in western North America that attack and mate on plants of Rosaceae (~60 taxa) and Caprifoliaceae (three taxa), respectively, likely contributing to partial reproductive isolation. Rhagoletis zephyria evolved from R. pomonella and is native to western North America, whereas R. pomonella was introduced there. Given that key features of the flies' ecology, breeding compatibility, and evolution differ, we predicted that adult eclosion patterns of the two flies from Washington State, USA are also distinct. When puparia were chilled, eclosion of apple- and black hawthorn-origin R. pomonella was significantly more dispersed, with less pronounced peaks, than of snowberry-origin R. zephyria within sympatric and nonsympatric site comparisons. Percentages of chilled puparia that produced adults were ≥67% for both species. However, when puparia were not chilled, from 13.5 to 21.9% of apple-origin R. pomonella versus only 1.2% to 1.9% of R. zephyria eclosed. The distinct differences in eclosion traits of R. pomonella and R. zephyria could be due to greater genetic variation in R. pomonella, associated with its use of a wider range of host plants than R. zephyria.

Evidence for spatial clines and mixed geographic modes of speciation for North American cherry-infesting Rhagoletis (Diptera: Tephritidae) flies.

An important criterion for understanding speciation is the geographic context of population divergence. Three major modes of allopatric, parapatric, and sympatric speciation define the extent of spatial overlap and gene flow between diverging populations. However, mixed modes of speciation are also possible, whereby populations experience periods of allopatry, parapatry, and/or sympatry at different times as they diverge. Here, we report clinal patterns of variation for 21 nuclear-encoded microsatellites and a wing spot phenotype for cherry-infesting Rhagoletis (Diptera: Tephritidae) across North America consistent with these flies having initially diverged in parapatry followed by a period of allopatric differentiation in the early Holocene. However, mitochondrial DNA (mtDNA) displays a different pattern; cherry flies at the ends of the clines in the eastern USA and Pacific Northwest share identical haplotypes, while centrally located populations in the southwestern USA and Mexico possess a different haplotype. We hypothesize that the mitochondrial difference could be due to lineage sorting but more likely reflects a selective sweep of a favorable mtDNA variant or the spread of an endosymbiont. The estimated divergence time for mtDNA suggests possible past allopatry, secondary contact, and subsequent isolation between USA and Mexican fly populations initiated before the Wisconsin glaciation. Thus, the current genetics of cherry flies may involve different mixed modes of divergence occurring in different portions of the fly's range. We discuss the need for additional DNA sequencing and quantification of prezygotic and postzygotic reproductive isolation to verify the multiple mixed-mode hypothesis for cherry flies and draw parallels from other systems to assess the generality that speciation may commonly involve complex biogeographies of varying combinations of allopatric, parapatric, and sympatric divergence.

Low Temperature Duration and Adult Rearing Regimes Affect Eclosion of Rhagoletis indifferens (Tephritidae: Diptera).

Western cherry fruit fly, Rhagoletis indifferens Curran, is a quarantine pest of sweet cherries in the Pacific Northwest of the United States that overwinters as diapausing pupae. Eclosion responses of R. indifferens puparia to different low temperature durations and postdiapause conditions affect the pest status of the fly. Here, we determined the effects of holding R. indifferens puparia at 3°C for 0, 1, 2, 5, 10, 15, and 20 wk on adult eclosion times and rates at two simulated temperate and two simulated tropical climate treatments over 40 wk. When puparia were chilled 0, 1, or 2 wk, adult eclosion across the four climate treatments displayed a bimodal distribution with low eclosion at 3 wk and high eclosion at 23-35 wk. When puparia were chilled ≤ 10 wk, there was a weaker bimodal distribution. However, when puparia were chilled 15-30 wk, eclosion was more synchronous and occurred at 5-7 wk across the four postchill climate treatments. Eclosion was greater at a postdiapause temperature of 26°C than 23°C. Timing to 50% eclosion was faster at longer photoperiod (16:8 L:D) than shorter (12:12 L:D). The bimodality of eclosion in respect to the duration of low temperature exposure may be indicative of univoltine insect species with obligate diapause that may span over two seasons.

Evaluation of Cyantraniliprole, Spinetoram, and Chromobacterium subtsugae Extract in Bait for Killing and Reducing Oviposition of Rhagoletis indifferens (Diptera: Tephritidae).

Insecticides mixed in sugar-protein baits or insecticides alone have been used to control tephritid fruit flies for many years. Here, effects of cyantraniliprole, spinetoram, and the biopesticide Chromobacterium subtsugae extract in sucrose-yeast extract bait or alone on kill and oviposition of western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), were evaluated in the laboratory. Flies were exposed to dry insecticide bait or insecticide alone in the presence or absence of a nontoxic food strip. Spinetoram alone caused greater mortality than cyantraniliprole alone, while cyantraniliprole in bait caused mortality as high as spinetoram bait and greater mortality than cyantraniliprole alone. Chromobacterium subtsugae extract alone but not in bait caused significant mortality compared with controls, but was much less effective than cyantraniliprole and spinetoram. Spinetoram alone reduced oviposition more than cyantraniliprole alone. However, cyantraniliprole bait reduced oviposition as much or more than spinetoram alone or spinetoram bait. Cyantraniliprole and spinetoram baits caused greater mortality when a nontoxic food strip was absent than present, but there was no corresponding reduction in oviposition. Chromobacterium subtsugae extract did not significantly reduce oviposition compared with controls. Potential benefits of using cyantraniliprole baits as an additional or alternative method to using more toxic spinosyn insecticides for controlling R. indifferens warrant study.

The Establishment Risk of Lycorma delicatula (Hemiptera: Fulgoridae) in the United States and Globally.

Native to Asia, the spotted lanternfly, Lycorma delicatula (White), is an emerging pest of many commercially important plants in Korea, Japan, and the United States. Determining its potential distribution is important for proactive measures to protect commercially important commodities. The objective of this study was to assess the establishment risk of L. delicatula globally and in the United States using the ecological niche model MAXENT, with a focus on Washington State (WA), where large fruit industries exist. The MAXENT model predicted highly suitable areas for L. delicatula in Asia, Oceania, South America, North America, Africa, and Europe, but also predicted that tropical habitats are not suitable for its establishment, contrary to published information. Within the United States, the MAXENT model predicted that L. delicatula can establish in most of New England and the mid-Atlantic states, the central United States and the Pacific Coast states, including WA. If introduced, L. delicatula is likely to establish in fruit-growing regions of the Pacific Northwest. The most important environmental variables for predicting the potential distribution of L. delicatula were mean temperature of driest quarter, elevation, degree-days with a lower developmental threshold value of 11°C, isothermality, and precipitation of coldest quarter. Results of this study can be used by regulatory agencies to guide L. delicatula surveys and prioritize management interventions for this pest.

Rapid and repeatable host plant shifts drive reproductive isolation following a recent human-mediated introduction of the apple maggot fly, Rhagoletis pomonella.

Ecological speciation via host-shifting is often invoked as a mechanism for insect diversification, but the relative importance of this process is poorly understood. The shift of Rhagoletis pomonella in the 1850s from the native downy hawthorn, Crataegus mollis, to introduced apple, Malus pumila, is a classic example of sympatric host race formation, a hypothesized early stage of ecological speciation. The accidental human-mediated introduction of R. pomonella into the Pacific Northwest (PNW) in the late 1970s allows us to investigate how novel ecological opportunities may trigger divergent adaptation and host race formation on a rapid timescale. Since the introduction, the fly has spread in the PNW, where in addition to apple, it now infests native black hawthorn, Crataegus douglasii, and introduced ornamental hawthorn, Crataegus monogyna. We use this "natural experiment" to test for genetic differentiation among apple, black, and ornamental hawthorn flies co-occurring at three sympatric sites. We report evidence that populations of all three host-associations are genetically differentiated at the local level, indicating that partial reproductive isolation has evolved in this novel habitat. Our results suggest that conditions suitable for initiating host-associated divergence may be common in nature, allowing for the rapid evolution of new host races when ecological opportunity arises.

Geographic and Ecological Dimensions of Host Plant-Associated Genetic Differentiation and Speciation in the Rhagoletis cingulata (Diptera: Tephritidae) Sibling Species Group.

Ascertaining the causes of adaptive radiation is central to understanding how new species arise and come to vary with their resources. The ecological theory posits adaptive radiation via divergent natural selection associated with novel resource use; an alternative suggests character displacement following speciation in allopatry and then secondary contact of reproductively isolated but ecologically similar species. Discriminating between hypotheses, therefore, requires the establishment of a key role for ecological diversification in initiating speciation versus a secondary role in facilitating co-existence. Here, we characterize patterns of genetic variation and postzygotic reproductive isolation for tephritid fruit flies in the Rhagoletis cingulata sibling species group to assess the significance of ecology, geography, and non-adaptive processes for their divergence. Our results support the ecological theory: no evidence for intrinsic postzygotic reproductive isolation was found between two populations of allopatric species, while nuclear-encoded microsatellites implied strong ecologically based reproductive isolation among sympatric species infesting different host plants. Analysis of mitochondrial DNA suggested, however, that cytoplasmic-related reproductive isolation may also exist between two geographically isolated populations within R cingulata. Thus, ecology associated with sympatric host shifts and cytoplasmic effects possibly associated with an endosymbiont may be the key initial drivers of the radiation of the R. cingulata group.

Modeling the abundance of two Rhagoletis fly (Diptera: Tephritidae) pests in Washington State, U.S.A.

Well-adapted and abundant insect pests can negatively affect agricultural production. We modeled the abundance of two Rhagoletis fly (Diptera: Tephritidae) pests, apple maggot fly, Rhagoletis pomonella (Walsh), and western cherry fruit fly, Rhagoletis indifferens Curran, in Washington State (WA), U.S.A. using biologically relevant environmental variables. We tested the hypothesis that abundance of the two species is influenced by different environmental variables, based on the fact that these two species evolved in different environments, have different host plants, and that R. pomonella is an introduced pest in WA while R. indifferens is native. We collected data on fly and host plant abundance at 61 randomly selected sites across WA in 2015 and 2016. We obtained land-cover, climate, and elevation data from online sources and used these data to derive relevant landscape variables and modeled fly abundance using generalized linear models. For R. pomonella, relatively high winter mean minimum temperature, low elevation, and developed land-cover were the top variables positively related to fly abundance. In contrast, for R. indifferens, the top variables related to greater fly abundance were high Hargreaves climatic moisture and annual heat-moisture deficits (indication of drier habitats), high host plant abundance, and developed land-cover. Our results identify key environmental variables driving Rhagoletis fly abundance in WA and can be used for understanding adaptation of insects to non-native and native habitats and for assisting fly quarantine and management decisions.

Three-Dimensional Versus Rectangular Sticky Yellow Traps for Western Cherry Fruit Fly (Diptera: Tephritidae).

The most effective traps tested against western cherry fruit fly, Rhagoletis indifferens Curran, have been the Yellow Sticky Strip (YSS) rectangle made of styrene and the three-dimensional yellow Rebell cross made of polypropylene. However, three-dimensional YSS styrene traps have never been tested against this or any other fruit fly. The main objectives of this study were to determine the efficacies of 1) YSS cross, Rebell cross, YSS cylinder, and YSS rectangle traps, 2) Rebell cross versus Rebell rectangle traps, and 3) YSS tent versus YSS rectangle traps for R. indifferens. For 1), the YSS cross caught more flies than the Rebell cross of equivalent surface area and more than a smaller YSS cylinder, but not any more than a YSS rectangle of similar surface area as the YSS cross. For 2), a Rebell cross caught more flies than a rectangle of equivalent surface area made of Rebell panels. For 3), YSS tent and YSS rectangle traps of equivalent surface area did not differ in fly captures. Results suggest that the YSS cross was more effective than the Rebell cross due to its color and that when trap color is highly attractive, three-dimensional shape may be unimportant, whereas it could be when trap color is less attractive. A new trap modeled after the YSS cross, compact but with high trap surface area to increase fly captures, could be an effective option or addition to rectangles for monitoring R. indifferens.

Spinosad Versus Spinetoram Effects on Kill and Oviposition of Rhagoletis indifferens (Diptera: Tephritidae) at Differing Fly Ages and Temperatures.

Western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), is a major quarantine pest of cherries (Prunus spp.) in western North America that is often managed using the organic insecticide spinosad, but there is a question of whether its semisynthetic relative spinetoram is more toxic and better to use for controlling the fly. Here, spinosad and spinetoram effects on R. indifferens kill and oviposition were determined by exposing 3-4, 7-10, or 14-18 d old flies to dry spinosad and spinetoram (0.21 or 0.33 mg active ingredient [a.i.] per dish) and untreated cherries or to insecticide-treated cherries at 15.6, 22.5, and 29.4°C. Kill was not affected by fly age. Spinetoram killed more female flies by day 1 than spinosad at all temperatures. In both treatments, kill was lower at 15.6°C than 22.5 and 29.4°C, although a difference between 22.5 and 29.4°C was detected more often in spinosad treatments. Both insecticides killed 3-4 d old flies quickly enough to prevent oviposition, but neither prevented oviposition by 7-10 and 14-18 d old flies. Significantly, oviposition by flies exposed to spinosad and spinetoram did not differ at any temperature. Results indicate spinetoram is more toxic to R. indifferens than spinosad. However, this higher toxicity is not needed to prevent oviposition by younger flies. Furthermore, spinetoram residues are not sufficiently toxic to kill older flies quickly enough to reduce oviposition more than spinosad. Taken together, these conclusions imply that spinosad and spinetoram are equal for controlling R. indifferens infestations.