Influence of habitat structure and resource availability on the movements of Rhagoletis indifferens (Diptera: Tephritidae)

Movement of Rhagoletis mendax (Diptera: Tephritidae) in Fruit-Bearing Wild Blueberry Fields. Part II

During dispersal into fruit-bearing wild blueberry fields, blueberry maggot flies were highly active during all daylight hours as revealed by trap captures, although in one trial afternoon activity was greater than morning activity. Flies were not captured in traps at night, although observations in growth chambers showed that their activity at night, measured as displacement of position, was equal to daylight conditions. Flies were shown to fly at low altitude, just above the crop canopy, and screen fencing was shown to be effective at reducing colonization of plots, presumably due to their low height during flight. Over a 4-yr mark-capture study, colonization rate was shown to be low at 9.7 m/d, although a separate 2010 study showed higher rates at 14.1 and 28.0 m/d. Movement was shown to be nondirectional or random in the field, but a constrained random walk exhibiting direction into the field. Weed cover and high fruit density were associated with higher fly relative abundance, suggesting these field characteristics served as attractors slowing colonization rate into a field. Transect trap studies showed the temporal and spatial pattern of fly colonization into commercial wild blueberry fields, one of a slow wave that penetrates into the field interior as the season progresses. There is also an increase in fly abundance within-field edges and adjacent forest. The 'stacking' of flies along a field edge and slow movement rate into a field was shown through simulation to be a result of nondirectional short-distance dispersal of flies.

Patterns of Oviposition and Feeding in the Monophagous Fly Anastrepha spatulata (Diptera: Tephritidae) on its Larval Host Plant Schoepfia schreberi

Monophagous insects that use discrete resources for oviposition and feeding are especially sensitive to variations in host quality and availability because their opportunities to find these resources are scarce. The monophagous tephritid fly Anastrepha spatulata Stone is a tephritid fly that uses as hosts the fruits of the non-economically important Schoepfia schreberi J. F. Gmel. Scant information of host utilization behavior in the field is available for this species. Wild individually marked flies were observed during the fruiting season. Observations of oviposition, feeding and resting on three trees were taken hourly from 0900 to 1800 hours on days with benign weather. Our results suggest that females can use fruits for oviposition or for feeding according to a temporal scale. Females were significantly more likely to feed on smaller hosts and oviposit in larger ones. Additionally, individual variation in host patch exploitation was detected. However, females that fed on a natural food source such as host fruit juice oviposited fewer eggs than females provided an artificial diet of sucrose and hydrolyzed yeast. Results indicate that females use different foraging tactics during the fruiting season and confirm that, in this case, the host plant is not the center of activity.

Validation of Individual-Based Markov-Like Stochastic Process Model of Insect Behavior and a "Virtual Farm" Concept for Enhancement of Site-Specific IPM

The paper reports application of a Markov-like stochastic process agent-based model and a "virtual farm" concept for enhancement of site-specific Integrated Pest Management. Conceptually, the model represents a "bottom-up ethological" approach and emulates behavior of the "primary IPM actors"-large cohorts of individual insects-within seasonally changing mosaics of spatiotemporally complex faming landscape, under the challenge of the local IPM actions. Algorithms of the proprietary PESTonFARM model were adjusted to reflect behavior and ecology of R. cerasi. Model parametrization was based on compiled published information about R. cerasi and the results of auxiliary on-farm experiments. The experiments were conducted on sweet cherry farms located in Austria, Germany, and Belgium. For each farm, a customized model-module was prepared, reflecting its spatiotemporal features. Historical data about pest monitoring, IPM treatments and fruit infestation were used to specify the model assumptions and calibrate it further. Finally, for each of the farms, virtual IPM experiments were simulated and the model-generated results were compared with the results of the real experiments conducted on the same farms. Implications of the findings for broader applicability of the model and the "virtual farm" approach-were discussed.

Chilling and Host Plant/Site-Associated Eclosion Times of Western Cherry Fruit Fly (Diptera: Tephritidae) and a Host-Specific Parasitoid

The western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), is an endemic herbivore of bitter cherry, Prunus emarginata (Douglas ex Hooker) Eaton, but ∼100 years ago established on earlier-fruiting domesticated sweet cherry, Prunus avium (L.) L. Here, we determined if eclosion times of adult R. indifferens from sweet and bitter cherry differ according to the phenology of their respective host plants and if eclosion times of the host-specific parasitoid Diachasma muliebre (Muesebeck) (Hymenoptera: Braconidae) attacking bitter and sweet cherry flies differ according to the eclosion phenology of their fly hosts. Fly pupae from sweet and bitter cherry fruit were collected from sympatric and allopatric sites in Washington state, and chilled at 5°C. Because timing of eclosion in R. indifferens depends on chill duration, eclosion time in wasps could also vary with chill duration. To account for this, fly pupae were chilled for 1, 2, 2.5, 3, 4, 6, or 8 mo. Both flies and wasps eclosed earlier with longer chill durations. Eclosion times of sweet and bitter cherry flies from a sympatric site in central Washington did not differ. However, at allopatric sites in northwestern and central Washington, bitter cherry flies eclosed later than sweet and bitter cherry flies at the sympatric site. Correspondingly, D. muliebre parasitizing a more isolated bitter cherry fly population eclosed later than D. muliebre parasitizing earlier-emerging sweet and bitter cherry fly populations. These results provide evidence for D. muliebre rapidly responding to changes in host plant shifts by R. indifferens.

Field type, trap type and field-edge characteristics affect Rhagoletis mendax captures in lowbush blueberries

BACKGROUND

Blueberry maggot, Rhagoletis mendax Curran (Diptera: Tephritidae), is the most important pest of blueberries in eastern North America. Insecticide use in fruit-bearing lowbush blueberry fields could be reduced with management strategies focused on vegetative fields. Fly distribution and fruit infestation levels were assessed where fruit-bearing and vegetative fields adjoin and along forested edges of vegetative fields.

RESULTS

Along adjoining edges, immature female flies were captured in fruiting fields and mature females in vegetative fields throughout the season. Male fly captures and fruit infestation levels were greater at 5 m than at 30 m from the edge. Along forested edges, fly captures were best predicted by densities of ripe lowbush blueberries and large coniferous trees. Maggot infestation level in lowbush blueberries was best predicted by blueberry density and small deciduous trees. Bunchberry, Cornus canadensis L., was the only non-crop host in which blueberry maggot was found.

CONCLUSIONS

We have shown that relatively high numbers of flies occur in vegetative fields and at edges of fruiting fields. Ripe blueberries and certain vegetation in forested edges affect fly distribution and probably maintain populations. These results may help to predict where controls for blueberry maggot should be targeted and suggest that management strategies focused on vegetative fields and field edges may be worthwhile.

Seasonal distributions of the western cherry fruit fly (Diptera: Tephritidae) among host and nonhost fruit trees

Seasonal distributions of the western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), in sweet cherry (Prunus avium (L.) L.) (major host), black hawthorn (occasional developmental host) (Crataegus douglasii Lindley), and other trees were determined in a ponderosa pine ecosystem in Washington state, USA. The hypothesis that most fly dispersal from cherry trees occurs after fruit senesce or drop was tested, with emphasis on movement to black hawthorn trees. Sweet cherry fruit developed earlier than black hawthorn, bitter cherry (common host), choke cherry, and apple fruit. Flies were usually captured first in sweet cherry trees but were caught in bitter cherry and other trees throughout the season. Peak fly capture periods in sweet cherry began around the same time or slightly earlier than in other trees. However, peak fly capture periods in black hawthorn and other nonsweet cherry trees continued after peak periods in sweet cherry ended, or relative fly numbers within sweet cherry declined more quickly than those within other trees. Larvae were reared from sweet and bitter cherry but not black hawthorn fruit. Results provide partial support for the hypothesis in that although R. indifferens commonly disperses from sweet cherry trees with fruit, it could disperse more, or more flies are retained in nonsweet cherry trees after than before sweet cherries drop. This could allow opportunities for the flies to use other fruit for larval development. Although R. indifferens infestation in black hawthorn was not detected, early season fly dispersal to this and other trees and fly presence in bitter cherry could make fly management in sweet cherry difficult.