Robert B. Goughnour

Host plant use by and new host records of apple maggot, western cherry fruit fly, and other Rhagoletis species (Diptera: Tephritidae) in western Washington state

Abstract Host plant use by apple maggot fly, Rhagoletis pomonella (Walsh), 1867, western cherry fruit fly, Rhagoletis indifferens Curran, 1932, and other Rhagoletis species (Diptera: Tephritidae) in western Washington state and northwestern Oregon was determined by rearing larvae in fruit to adults in 2004 to 2006. Rhagoletis pomonella infested apple, Malus domestica (Borkh.) Borkh., crab apple, Malus spp., Suksdorfs hawthorn, Crataegus suksdorfii (Sarg.) Kruscke, and English hawthorn, Crataegus monogyna Jacq. Also infested were apricot, Prunus armeniaca L., and cherry plum, Prunus cerasifera Ehrh., which are two new Washington host records for R. pomonella, and smooth hawthorn, Crataegus laevigata (Poiret) DC., Japanese plum, Prunus salicina Lindl., European mountain ash, Sorbus aucuparia L., western mountain ash, Sorbus scopulina Greene, parney cotoneaster, Cotoneaster lacteus W. W. Smith, and European cotoneaster, Cotoneaster integerrimus Medic., which are six new host records for R. pomonella. Rhagoletis indifferens infested bird cherry, Prunus padus L., and cherry plum, P. cerasifera, which are two new host records. Three, one, and one new host records were also determined for Rhagoletis tabellaria (Fitch), 1855, Rhagoletis zephyria Snow, 1894, and Rhagoletis completa Cresson, 1929, respectively. In the coast forest ecosystem of western Washington, the host breadth of both R. pomonella and R. indifferens are relatively broad, perhaps in part because of large fly populations. The discovery of 13 new hosts in western Washington suggests this region can yield a wealth of information on the adaptability of various Rhagoletis to diverse plants and host race formation in this genus.

BEHAVIORAL EVIDENCE FOR FRUIT ODOR DISCRIMINATION AND SYMPATRIC HOST RACES OF RHAGOLETIS POMONELLA FLIES IN THE WESTERN UNITED STATES

The recent shift of Rhagoletis pomonella (Diptera: Tephritidae) from its native host downy hawthorn, Crataegus mollis, to introduced domesticated apple, Malus domestica, in the eastern United States is a model for sympatric host race formation. However, the fly is also present in the western United States, where it may have been introduced via infested apples within the last 60 years. In addition to apple, R. pomonella also infests two hawthorns in the West, one the native black hawthorn, C. douglasii, and the other the introduced English ornamental hawthorn, C. monogyna. Here, we test for behavioral evidence of host races in the western United States. through flight tunnel assays of western R. pomonella flies to host fruit volatile blends. We report that western apple, black hawthorn, and ornamental hawthorn flies showed significantly increased levels of upwind‐directed flight to their respective natal compared to nonnatal fruit volatile blends, consistent with host race status. We discuss the implications of the behavioral results for the origin(s) of western R. pomonella, including the possibility that western apple flies were not introduced, but may represent a recent shift from local hawthorn fly populations.

A field test for host fruit odour discrimination and avoidance behaviour for Rhagoletis pomonella flies in the western United States

Prezygotic isolation due to habitat choice is important to many models of speciation‐with‐gene‐flow. Habitat choice is usually thought to occur through positive preferences of organisms for particular environments. However, avoidance of non‐natal environments may also play a role in choice and have repercussions for post‐zygotic isolation that preference does not. The recent host shift of Rhagoletis pomonella (Diptera: Tephritidae) from downy hawthorn, Crataegus mollis, to introduced apple, Malus domestica, in the eastern United States is a model for speciation‐with‐gene‐flow. However, the fly is also present in the western United States where it was likely introduced via infested apples ≤ 60 years ago. R. pomonella now attacks two additional hawthorns in the west, the native C. douglasii (black hawthorn) and the introduced C. monogyna (English ornamental hawthorn). Flight tunnel tests have shown that western apple‐, C. douglasii‐ and C. monogyna‐origin flies all positively orient to fruit volatile blends of their respective natal hosts in flight tunnel assays. Here, we show that these laboratory differences translate to nature through field‐trapping studies of flies in the state of Washington. Moreover, western R. pomonella display both positive orientation to their respective natal fruit volatiles and avoidance behaviour (negative orientation) to non‐natal volatiles. Our results are consistent with the existence of behaviourally differentiated host races of R. pomonella in the west. In addition, the rapid evolution of avoidance behaviour appears to be a general phenomenon for R. pomonella during host shifts, as the eastern apple and downy hawthorn host races also are antagonized by non‐natal fruit volatiles.

The Geographic Distribution of Rhagoletis pomonella (Diptera: Tephritidae) in the Western United States: Introduced Species or Native Population?

ABSTBACT The apple maggot fly, Rhagoletis pomonella Walsh (Diptera: Tephritidae), is a major pest of commercially grown domesticated apple (Malus domestica Borkhausen) in North America. The shift of the fly from its native host hawthorn (Crataegus mollis) to apple in the eastern United States is often cited as an example of incipient sympatric speciation in action. However, R. pomonella is also present in the Pacific Northwest region of the United States where it infests apple, native black hawthorn (Crataegus douglasii), and introduced English ornamental hawthorn (C. monogyna). It is believed that R. pomonella was introduced to the Portland, OR, area via larval-infested apples from the east. The fly subsequently spread through the region, shifting onto black hawthorn and ornamental hawthorn as additional hosts as it spread. It is also possible, however, that R. pomonella is native to black hawthorn in the Pacific Northwest and switched to infest apple and ornamental hawthorn after the introduction of these two alternative hosts to the region. Here, we document the distribution of R. pomonella through the Pacific Northwest and Rocky Mountain states of the western United States to help clarify the origin (s) of the fly outside the eastern United States. We report a distribution pattern consistent with the hypothesis that R. pomonella was introduced to the Pacific Northwest via infested apples. In particular, the low levels or lack of C. dougliasii-infesting R. pomonella east of the Cascade Mountains in the states of Washington, OR, and Idaho implies that the fly is not native on black hawthorn and is of recent origin. We discuss the evolutionary and applied implications of the results with respect to our current understanding of host race formation and control for R. pomonella.

Abundance of Apple Maggot, Rhagoletis pomonella, Across Different Areas in Central Washington, with Special Reference to Black-Fruited Hawthorns

Abstract The apple maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), infests non-commercial apple (Malus domestica (Borkh.) Borkh.) and native black-fruited hawthorns (mostly Crataegus douglasii Lindl.) in central Washington, but little has been published on the abundance of the fly in this region. In this paper, the abundance of R. pomonella across different sites near apple-growing areas in central Washington is documented in order to assess the threat of the fly to commercial apple orchards. The fly was first detected on traps in Klickitat, Yakima, and Kittitas Counties in 1981, 1995, and 1997, respectively. From 1981–2010 in Kittitas and Yakima Counties, only 0 to 4.7% of traps on apple, crabapple, and hawthorn trees were positive for flies, whereas in Klickitat County, located farther from commercial apple orchards, 0 to 41.9% of traps were positive. In 2008, in Yakima County and Goldendale in Klickitat County, 7.8% of black-fruited hawthorn trees were infested, with 0 to 0.00054 larvae per fruit. In 2010, in Kittitas and Yakima Counties and Goldendale in Klickitat County, 25.0% of C. douglasii trees were infested, with 0.00042 to 0.00248 larvae per fruit. In 2010, in a remote forested area of Klickitat County far from commercial apple orchards, 94.7% of C. douglasii trees were infested, with 0.20813 larvae per fruit. Overall results suggest R. pomonella is unlikely to develop high populations rapidly near major commercial apple-growing areas in central Washington, including in black-fruited hawthorns, increasing chances it can be kept out of commercial orchards.

Ammonium Carbonate is More Attractive than Apple and Hawthorn Fruit Volatile Lures to Rhagoletis pomonella (Diptera: Tephritidae) in Washington State

ABSTRACT The apple maggot fly, Rhagoletis pomonella (Walsh), is an introduced, quarantine pest of apple (Malus domestica Borkhausen) in the Pacific Northwest of the United States. In the eastern United States where the fly is native, fruit volatiles have been reported to be more attractive than ammonia compounds to R. pomonella. However, the opposite may be true in the western United States. Here, we determined whether newly identified western apple and western hawthorn fruit volatiles are more attractive than ammonium carbonate (AC) to R. pomonella in apple, black hawthorn, and ornamental hawthorn trees in western Washington State. In all three host trees, sticky red sphere or yellow panel traps baited with AC generally caught more flies than traps baited with lures containing the four newly developed fruit blends (modified eastern apple, western apple, western ornamental hawthorn, and western black hawthorn) or two older blends (eastern apple and eastern downy hawthorn). Fruit volatiles also displayed more variation among trapping studies conducted at different sites, in different host trees, and across years than AC. The results imply that traps baited with AC represent the best approach to monitoring R. pomonella in Washington State.

Differences in Body Size and Egg Loads of Rhagoletis indifferens (Diptera: Tephritidae) from Introduced and Native Cherries

ABSTRACT The western cherry fruit fly, Rhagoletis indifferens Curran, infests introduced, domesticated sweet [Prunus avium (L.) L. ], and tart cherries (Prunus cerasus L.) as well as native bitter cherry, Prunus emarginata (Douglas) Eaton. Bitter cherries are smaller than sweet and tart cherries and this could affect various life history traits of flies. The objectives of the current study were to determine 1) if body size and egg loads of flies infesting sweet, tart, and bitter cherries differ from one another; and 2) if any observed body size differences are genetically based or caused by the host fruit environment. Pupae and adults of both sexes reared from larval-infested sweet and tart cherries collected in Washington and Montana were larger than those reared from bitter cherries. In addition, flies of both sexes caught on traps in sweet and tart cherry trees were larger than those caught in bitter cherry trees and females trapped from sweet and tart cherry trees had 54.0–98.8% more eggs. The progeny of flies from naturally-infested sweet and bitter cherries reared for one generation in the laboratory on sweet cherry did not differ in size. The same also was true for progeny of sweet and bitter cherry flies reared in the field on bitter cherry. The results suggest that the larger body sizes of flies from sweet and tart cherries than bitter cherries in the field are caused by host fruit and not genetic factors.

Hybridization and the spread of the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae), in the northwestern United States.

Hybridization may be an important process interjecting variation into insect populations enabling host plant shifts and the origin of new economic pests. Here, we examine whether hybridization between the native snowberry‐infesting fruit fly Rhagoletis zephyria (Snow) and the introduced quarantine pest R. pomonella (Walsh) is occurring and may aid the spread of the latter into more arid commercial apple‐growing regions of central Washington state, USA. Results for 19 microsatellites implied hybridization occurring at a rate of 1.44% per generation between the species. However, there was no evidence for increased hybridization in central Washington. Allele frequencies for seven microsatellites in R. pomonella were more ‘R. zephyria‐like’ in central Washington, suggesting that genes conferring resistance to desiccation may be adaptively introgressing from R. zephyria. However, in only one case was the putatively introgressing allele from R. zephyria not found in R. pomonella in the eastern USA. Thus, many of the alleles changing in frequency may have been prestanding in the introduced R. pomonella population. The dynamics of hybridization are therefore complex and nuanced for R. pomonella, with various causes and factors, including introgression for a portion, but not all of the genome, potentially contributing to the pest insects spread.

Mating Frequencies and Production of Hybrids by Rhagoletis pomonella and Rhagoletis zephyria (Diptera: Tephritidae) in the Laboratory

Abstract Evidence indicates low levels of hybridization in nature between the apple maggot (AM), Rhagoletis pomonella (Walsh), and snowberry maggot (SB), Rhagoletis zephyria Snow, sibling species in the R. pomonella complex. We determined the effects of AM and SB pairings on mating frequencies and production of hybrid offspring in the laboratory. Mating frequency was lowest in SB female × AM male pairings, higher in AM female × SB male and AM female × AM male pairings, and highest in SB female × SB male pairings. A greater percentage of AM female × AM male pairs produced offspring (puparia) than did AM female × SB male and SB female × AM male pairs, and a greater percentage of AM female × SB male pairs produced puparia than did SB female × AM male pairs. Male or female F1 hybrids backcrossed with AM males and with other F1 hybrids were fertile. Results suggest most R. pomonella × R. zephyria hybrids found in nature are the result of R. zephyria males mating with R. pomonella females, with few from reciprocal matings. If true, this asymmetry could lower the incidence of hybridization in nature.

Differential Captures of Rhagoletis pomonella (Diptera: Tephritidae) on Four Fluorescent Yellow Rectangle Traps

ABSTRACT Four commercial sticky fluorescent yellow rectangle traps differing in shades of yellow, fluorescence, and other features were compared for capturing apple maggot fly, Rhagoletis pomonella (Walsh). Traps were the Alpha Scents Yellow Card (Alpha Scents), Pherocon® AM (Pherocon), Multigard® AM (Multigard), and the Stiky™ Strips Insect Trap (Olson, small and large sizes), all baited with the same ammonium bicarbonate lure. L*, a*, and b* color space values indicated that the Alpha Scents trap was whiter (higher L*) and greener (lower a*) than the other traps, less yellow than the Pherocon trap, and more yellow (higher b*) than Multigard and Olson traps. The Pherocon trap had the highest relative fluorescence and was the brightest trap, followed in order by Multigard, Olson, and Alpha Scents traps. Various modified forms of the Alpha Scents trap captured significantly (1.5–6.4 times) more R. pomonella in choice tests than the Pherocon trap. The Alpha Scents trap captured 1.3–3.6 times more R. pomonella in paired choice tests than Pherocon, Multigard, and small and large Olson traps, and the Pherocon trap caught 1.4 times more R. pomonella than the Multigard trap (the Olson traps were not compared with these two traps). A combination of color and fluorescence features in the Alpha Scents trap could have contributed to its superior performance. These results suggest the Alpha Scents trap could be an alternative to the other traps tested for monitoring R. pomonella.