Drosophila immigrans

Larvae can be distinguished from Drosophila suzukii using PCR-RFLP analysis with XmnI restriction enzyme: D. immigrans produces two bands at 270bp and 310bp, while D. suzukii produces three bands at 120bp, 210bp, and 250bp. Distinguished from D. melanogaster by stronger association with Penicillium-infected citrus fruit and greater larval survival on mouldy citrus.

Adults are typical small vinegar flies. Eggs are white, elliptical, approximately 0.5 mm in length, with two chorionic filaments. Larvae have three instars: first instar 2.0-2.5 mm, second instar 4.0-4.5 mm, third instar 6.0-6.5 mm. Pupae are 3.5 mm, tan to dark brown in color. Body melanization varies clinally with altitude in montane populations.

Associated with citrus fruits, particularly those infected with Penicillium italicum or P. digitatum moulds. In montane habitats, found at altitudes from 600 to 2202 meters. Unable to overwinter outdoors in temperate regions at altitudes of 500m or higher in central Japan; populations in these areas maintained by migration from warmer areas.

Native to tropical/subtropical regions; populations in temperate montane areas (central Japan, alt. 500-2000m) maintained by seasonal migration. Present in the Philippines (Los Baños, Laguna). Records from Flores, Pico, São Miguel, Terceira (Azores), and Galápagos Islands.

In central Japan, present at lowlands (500-1200m) in spring and autumn, absent in summer due to heat intolerance; present at highlands (1500-2000m) only in summer. Seasonal migration occurs to escape temperature extremes; no photoperiodic diapause.

Larvae feed on standard Drosophila medium (banana-agar) in laboratory conditions. In nature, strongly associated with citrus fruits infected with Penicillium italicum or P. digitatum moulds; larvae survive better than D. melanogaster on Penicillium-infected citrus.

• Penicillium italicum - associated withSpecialist mould of citrus; D. immigrans larvae survive well on infected fruit
• Penicillium digitatum - associated withSpecialist mould of citrus; D. immigrans larvae survive well on infected fruit
• Citrus - breeding substratePrimary breeding site, especially when infected with Penicillium moulds

Complete metamorphosis with egg, three larval instars, prepupa, pupa, and adult stages. Total developmental period from egg to adult emergence averages 10 days (range 9-11 days) at 25±1°C: egg stage 1 day, larval stage 4 days (1st instar 1 day, 2nd instar 1 day, 3rd instar 2 days), prepupal stage 1 day, pupal stage 4 days. Adult lifespan averages 30 days. Egg production averages 50 eggs per female.

Larvae exhibit negative phototaxis and positive geotaxis. Adults exhibit positive phototaxis and negative geotaxis. Males follow females and mount for mating. Undergoes seasonal migration between lowland and highland areas to escape temperature extremes; less cold-hardy but more heat-tolerant than D. curviceps.

Used as a model organism in evolutionary studies to understand how viruses evolve with their hosts. Potential pest of citrus fruits, particularly in commercial settings where Penicillium infections occur. May have evolved as a citrus specialist and become domesticated as citrus exploitation expanded commercially.

• Drosophila suzukiiBoth species occur in similar habitats and can be confused in field collections; distinguished by PCR-RFLP banding patterns and larval survival on different substrates
• Drosophila melanogasterBoth common vinegar flies associated with fruit; D. immigrans more specialized on Penicillium-infected citrus with better larval survival on mouldy fruit, while D. melanogaster more common on uninfected fruit
• Drosophila curvicepsMember of same species group; D. immigrans is less cold-hardy but more heat-tolerant, with different seasonal migration patterns

• vinegar fly
• citrus pest
• seasonal migrant
• Penicillium association
• thermal adaptation
• altitudinal variation
• laboratory model

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
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