Strange Little Flies in the Big City: Exotic Flower-Breeding Drosophilidae (Diptera) in Urban Los Angeles

Urban landscapes are commonly considered too mundane and corrupted to be biotically interesting. Recent insect surveys employing 29 Malaise traps throughout Los Angeles, California, however, have uncovered breeding populations of two unexpected species of one of the most studied and familiar groups of organisms, Drosophila “fruit” flies. Unlike most introduced species of drosophilids, which breed in fresh or decaying fruits, these are specialized flower-breeders. A common species in the survey was Drosophila (Drosophila) gentica Wheeler and Takada, previously collected only once, in El Salvador. It belongs to the flavopilosa species group, all species of which have been known until now from central Chile, Argentina and Uruguay, to Veracruz, Mexico and the Caribbean, breeding in flowers of Cestrum (“jessamine”) and Sessea (Solanaceae). The Los Angeles populations are probably breeding in a native and/or introduced Cestrum; in addition, populations in San Luis Obispo County were visiting ornamental Cestrum. Drosophila gentica occurs as far north as San Francisco, where it was found breeding in Cestrum aurantiacum. D. gentica is redescribed and figured in detail for diagnostic and identification purposes. Specimens from Jamaica previously identified as D. gentica are a distinct species but are not formally described in lieu of complete male specimens. Rare in the Malaise traps was Drosophila (Sophophora) flavohirta Malloch, a common species in Australia on the blossoms of native Myrtaceae, found on introduced Eucalyptus in South Africa and both Eucalyptus and Syzygium in Madagascar; adults feed on myrtaceous pollen and nectar, larvae breed in the flowers. It is also redescribed in detail, including its unusual egg. This is the first New World report of this species; DNA sequences confirm it is a morphologically highly aberrant member of the D. melanogaster species group. This study reveals how intensive field sampling can uncover remarkable biodiversity in even the most urbanized areas.

城市景观通常被视作过于平庸且受人类活动破坏，难以具备值得关注的生物多样性价值。然而，研究人员在加利福尼亚州洛杉矶全市布设29台马氏诱捕器（Malaise trap）开展昆虫调查，却意外发现了一类被研究最多、最广为人知的生物类群——果蝇属（Drosophila，俗称“果实蝇”）的两个物种的繁殖种群。与多数以新鲜或腐烂果实为繁殖基质的果蝇科入侵物种不同，这两个物种为特化的花栖繁殖者。本次调查中的常见物种为*Drosophila (Drosophila) gentica* Wheeler & Takada，此前仅在萨尔瓦多有过一次采集记录。该物种隶属于黄绒果蝇种组（flavopilosa species group），此前所有已知该组物种的分布范围涵盖智利中部、阿根廷、乌拉圭，北至墨西哥韦拉克鲁斯州及加勒比地区，均以夜香树属（Cestrum，俗称“素馨”）和睡茄属（Sessea，茄科）的花朵作为繁殖基质。洛杉矶的果蝇种群大概率以本土或引入种植的夜香树属植物为繁殖宿主；此外，圣路易斯奥比斯波县的种群则取食观赏类夜香树属植物。*D. gentica*的分布北至旧金山，曾在当地被发现以黄花夜香树（Cestrum aurantiacum）为繁殖宿主。为便于分类鉴定与物种诊断，本研究对*D. gentica*进行了详细的重新描述与形态绘图。此前被鉴定为*D. gentica*的牙买加标本实则为另一独立物种，但由于缺乏完整的雄性标本，尚未进行正式分类描述。马氏诱捕器中较为稀有的物种为*Drosophila (Sophophora) flavohirta* Malloch。该物种在澳大利亚本土桃金娘科（Myrtaceae）植物的花上十分常见；在南非，其被发现于引入种植的桉树（Eucalyptus）上，在马达加斯加则见于桉树与蒲桃属（Syzygium）植物。成虫以桃金娘科植物的花粉与花蜜为食，幼虫则在花中繁殖。本研究同样对该物种进行了详细的重新描述，包括其形态特殊的卵。这是该物种首次在新大陆（New World）被报道；DNA序列分析证实，它是黑腹果蝇种组（D. melanogaster species group）中形态极为特化的一支。本研究表明，即便在城市化程度最高的区域，高强度的野外采样也能发掘出令人惊叹的生物多样性。