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

Diapause of the Western cherry fruit fly, Rhagoletis indifferens (Diptera: Tephritidae): metabolic rate and overwintering adaptations

The Western cherry fruit fly, Rhagoletis indifferens (Curran), is a Tephritid fly in the Pacific Northwest and is known to infest native bitter cherry, Prunus emarginata (Douglas ex Hooker), which is distributed throughout the Cascade Mountain range. This species occupies temperate to alpine climates and exhibits overwintering adaptations of diapause and supercooling. Isothermal and differential scanning calorimetry were used to determine the effects of diapause chilling duration and post-chilling warm rearing on the metabolic rate and supercooling point of R. indifferens. Previous studies have included the effects of chilling duration on post-diapause development and emergence as well as on the levels of metabolic reserves. Metabolic rate of R. indifferens, was used to calculate the ability of this species to remain in diapause for more than 1 yr as well as predicting the potential effects of climate change on the future abundance and distribution. It was determined that R. indifferens could diapause for more than 1 yr based on the levels of metabolic reserves and metabolic rate.

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.

Using the rDNA Internal Transcribed Spacer 1 to Identify the Invasive Pest Rhagoletis cerasi (Diptera: Tephritidae) in North America

The cherry-infesting fruit fly Rhagoletis cerasi Loew is a significant commercial pest in Europe that has recently invaded North America. To date, it has been trapped only in Canada and northwestern counties of New York. It has the potential to spread further and threaten production and movement of cherry commodities. Timely diagnosis of the pest will facilitate surveys and quick response to new detections. Adult morphology of the pest is distinct from other flies in North America. However, when flies are significantly damaged on traps or the immature life stages are found in fruits, molecular methods of identification are important to confirm presence and host-use records. Other than DNA sequencing of genes from flies which takes over a day to complete, there are no timely methods of molecular identification for this pest. In this study, we report the first sequence record of the internal transcribed spacer 1 (ITS1) from R. cerasi and develop two diagnostic tests for the pest based on ITS1 differences among species in North America. The tests use loop-mediated isothermal amplification (LAMP) and multiplex, conventional polymerase chain reaction (mcPCR) technologies that target the same region of the R. cerasi ITS1 sequence. Both tests performed well when tested against collections of R. cerasi from North America and Europe, generating Diagnostic Sensitivity estimates of 98.4-99.5%. Likewise, the tests had relatively high estimates of Diagnostic Specificity (97.8-100%) when tested against Rhagoletis Loew species present in North America that also use cherry as a developmental host.

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.