Rhagoletis mendax

Eggs are white and elongate in shape.[1] Full-grown larvae or maggots are 7.75mm (5/16 inches) long, off white, with large preoral teeth (in front of the mouth), a cone-shaped distal sensory organ at the head, and large anal lobes and paired spiracles located on the blunt posterior.[2][1][3] The pupa is encased in a brown outer skin known as a puparium. Adults are the most distinguishable of the life stages from other Rhagoletis species - mainly by the ratio of banding on their wings, ovipositor length and other genital features - and can be identified using a taxonomic identification key.[3][4] The female fly is approximately 4.75 mm (3/16 inch) long with a wingspan of 8mm (1/3 inch), with male flies being slightly smaller.[1] The thorax of both males and females is mostly black with a conspicuously white spot covering the scutellum and a white stripe on either side.[1][4] The abdomen of females is pointed and has four horizontal bands of fine white setae separating the sections, while the male abdomen is more rounded and has only three horizontal bands of setae.[1][4] The head is almost entirely covered by the eyes which are red in color, with a protruding pair of aristate antennae. They possess a single set of wings, which are clear with conspicuous dark black bands arranged in an "F" pattern. In many cases, visually distinguishing stages of R. mendax from others in the pomonella species group is not possible and may require the use of biochemical tests such as PCR to conclusively determine the species.[2][3][4]

Rhagoletis mendax life cycle

The life cycle of this species is holometabolous, and has four stages of development: egg, larva, pupa and adult. Adults typically have a lifespan of 30–45 days or longer, with females being capable of reproduction starting at 15 days and going to approximately 45 days (weather dependent).[2]

The phenology of the blueberry maggot is varied, and depends on the geographic region the population inhabits.[2] In most regions of North America, populations have a univoltine life cycle. In Maine and potentially other locations however approximately 85% of the population in the state is univoltine, while the rest are semivoltine: 10% spend three winters as pupae, and 5% spend four winters.[2]

In the spring or summer the first wave of adults will emerge from the soil, coinciding with or just before ripening of the host fruit in the region.[2] Adults will continue emerging in groups into the summer.[1] Approximately 90% of the population emerges within a one-month period of each other, however, females will emerge 4–5 days before males at the time of maximum fruit availability.[2] Emergence is delayed to summer in some areas, potentially due to heat-induced quiescence of pupae.[2]

Adults will feed on dew, insect honeydew, and other secretions on foliage until the females become sexually mature.[1] After mating, female flies will lay a single egg per berry using a retractable ovipositor on the end of their abdomen to pierce the fruit and deposit the egg just under the skin.[1] The process leaves behind an oviposition-deterring pheromone to prevent other females from laying their egg in the same fruit for a couple of days.[2][1]

Eggs will hatch in 3–7 days depending upon geographic location and climate, and the larvae will begin consuming the fruit.[3] Larvae will continue to feed and go through three instars of growth in 17–30 days, at which point third instar larvae will emerge from the fruit, drop to the soil, and begin pupating at a depth of one to two inches.[2][1] Pupation can commence in July at the southernmost limits of its distribution and into late September at its northernmost limits.[2]

Rhagoletis mendax is native to North America, and is found in the eastern regions of the United States and Canada.[2][3] As of 2015 in the United States its distribution reaches as far south as states such as Georgia and Florida, and as far northwest as states such as Maine and Vermont.[2] In Canada, it is present in all coastal eastern provinces excluding Newfoundland and Labrador ( New Brunswick, Nova Scotia, Quebec, & Ontario), and only in small populations in Quebec and Ontario.[5]

The primary mode of dispersal to new areas is through transport of infected fruit, and secondly through flight, as R. mendax adults can only fly short distances.[3] Pupae can also be transported in contaminated growing media.[3]

Rhagoletis mendax adults are attracted to a wide range of species in their host genus Ericaceae, and prefer them to the hosts of other Rhagoletis species.[2][3]

Of the Ericaceae genera, many hosts are commercial crops and wild species of the genus Vaccinium, such as highbush and lowbush blueberries (V. corymbosum & angustifolia respectively), cranberries (v. macrocarpon), lingonberries (V. vitis-idaea), and huckleberries (Vaccinium sp. & Gaylussacia sp).[3][6]

Some research shows that adults are also attracted to volatiles secreted by Enterobacter (Pantoea) agglomerans, an epiphytic nitrogen-fixing species of bacteria found on the leaves and fruit of plants.[2] This may be due to a symbiotic relationship between the two species, where E. agglomerans provides nitrogen necessary for maturation of the female's ovaries.[2]

Larva feeding on berries from within can result in premature fruit drop and loss of structural integrity.[7][8] Additionally, the presence of larvae in commercially grown berries can negatively impact consumer satisfaction. These factors lead to loss of marketability of the fruit and a reduction in profits for the grower.[8]

• Species description
• Photos and diagrams