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.

Mating frequencies and production of hybrids by Rhagoletis pomonella and Rhagoletis zephyria (Diptera: Tephritidae) in the laboratory

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.

OPIINE PARASITOIDS (HYMENOPTERA: BRACONIDAE) OF RHAGOLETIS POMONELLA AND R. ZEPHYRIA (DIPTERA: TEPHRITIDAE) IN THE WILLAMETTE VALLEY, OREGON

Two species of opiine (Braconidae) parasitoids, Opius lectoides Gahan and O. downesi Gahan parasitized Rhagoletis zephyria Snow and R. pomonella (Walsh) in the Willamette Valley, OR. Almost equal numbers of O. lectoides and O. downesi were recorded from R. zephyria, whereas about 91% of the opiines associated with R. pomonella were O. downesi. In general, percent parasitization of R. pomonella was variable from sample to sample, but substantially higher on hawthorn than on apple fruit. It appears that both the opiine species have made a rapid host shift from R. zephyria to newly introduced populations of R. pomonella.