Rhagoletis juglandis

R. juglandis was first described by E. T. Cresson, Jr. in 1920 from material from the exocarp of fruit of Juglans regia (the English or Persian walnut tree) in Arizona. == Taxonomy ==

R. juglandis belongs to the genus Rhagoletis and the family Tephritidae. == Morphology ==

The eggs appear a pearly white color when first laid, but progressively darken as the embryo develops. The eggs are somewhat curved, with one end slightly tapered and the other end pointed. The eggs measure to be around 0.8 mm by 0.3 mm. Upon developing into larvae, these flies take on a transparent look in their early stages and turn creamy white or light yellow as they mature. In addition, they have prominent anterior and posterior orange-yellow spiracles. The larvae measure to be around 9 mm by 2 mm. The pupae are described as looking like grains of wheat, with a barrel shape and straw color. The pupae measure around 5 mm by 3 mm. As adults, the main body color of the adult fly is tawny with lemon yellow markings. The wings look translucent and have three parallel transverse dark bands. The distal band continues along the costal margin to the apex (dorsal region). The abdomen of the fly has dark transverse bands on the dorsum. The female fly is larger than the male, and has a more pointed end of its abdomen due to the telescoping ovipositor. Females grow to be around 4 mm long in body length. == Distribution and habitat ==

There are recorded sightings of R.juglandis in Arizona, California, Texas, and Kansas. This North American pest also reached Europe in the late 1980s and is causing important damage to its principal host, the walnut. The husk fly also infests ripe apricot and peach fruits, usually if infested walnuts are located within flying distance. == Life history ==

Oviposition R. juglandis is univoltine, similar to its close relative R. suavis. Female flies do not completely develop eggs for oviposition until 7 to 14 days after emerging from the soil. Copulation and oviposition occur in the morning or late afternoon and evening. The female searches for a suitable spot for oviposition; when one is found, she forces her ovipositor several millimeters into the husk of the walnut. She then moves her body around in a semicircle to lacerate the tissue of the inner husk and create a cavity for the eggs. The female oviposits eggs below the surface of the husk of walnuts in batches of about 15 eggs. Oviposition takes several minutes. The spot of oviposition darkens after one or two days; then, the egg cavity can be detected with the naked eye. Larvae spend the winter in the pupal stage in the soil at around a depth of 1 to 4 inches. In mid to late summer, adult flies emerge from soil prior to ripening of walnut husks and emergence declines in number by September. == Food resources ==

R. juglandis flies deposit their eggs in the husks of developing walnuts, on which the larvae feed and develop. Adult flies feed on dew and plant sap and can also dissolve solid deposits on foliage for nutrients using saliva. Feeding is most active in the beginning of the day and in the evening. == Behavior ==

Mating Courtship behaviors are generally rare in the genus. However, R. juglandis is unique in its courtship signaling behaviors. Male flies demonstrate low-frequency wing vibration, accompanied by airborne infrasound. These bouts of vibration typically last from 5 seconds-15 minutes. Male flies raise their wings during these displays, turning the edges upward. R. juglandis participate in a resource-defense mating system. In addition, researchers have found that flies seem to internalize changes in sex ratio in the surrounding environment and respond accordingly. The effect of male density on copulation is stronger than female density. Individual flies copulate for longer in these male-biased environments. Superparasitism Superparasitism is the use of hosts that already contain a brood from the same species of parasite. R. juglandis females drag their ovipositors on the husk of the walnut after oviposition, which suggests that they have released a marking pheromone, a behavior typical of the Rhagoletis genus. However, the flies reinfest the same walnuts, and even the same oviposition sites, created by individuals of the same species. This occurs even when there are still uninfested hosts available. In large, less-infested walnut fruits, adult fly size has been found to be larger and larval survival is higher. == Interactions with humans ==

R. juglandis infests walnut trees, which has economic importance due to the cultivation of walnuts for human use. == References ==