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The causes of high biological diversity in biodiversity hotspots have long been a major subject of study in conservation biology. To investigate this matter, we conducted a phylogeographic study of five Drosophila (Diptera: Drosophilidae) species from East and Southeast Asia: Drosophila albomicans Duda , D. formosana Duda, D. immigrans Sturtevant, D. melanogaster Meigen, and D. simulans Sturtevant. We collected 185 samples from 28 localities in eight countries. From each collected individual, we sequenced the autosomal extra sex comb gene ( esc ) and seven mitochondrial genes, including nicotinamide adenine dinucleotide hydrate-reductase dehydrogenase subunit 4 ( ND4 ), ND4L , tRNA-His , tRNA-Pro , tRNA-Thr , partial ND5 , and partial ND6 . Phylogenetic analyses using maximum- likelihood and Bayesian methods revealed interesting population structure and identified the existence of two distinct D. formosana lineages (Southeast Asian and Taiwanese populations). Genetic differentiation among groups of D. immigrans suggests the possibility of endemic speciation in Taiwan. In contrast, D. melanogaster remained one extensively large population throughout East and Southeast Asia, including nearby islets. A molecular clock was used to estimate divergence times, which were compared with past geographical events to infer evolutionary scenarios. Our findings suggest that interglacial periods may have caused population isolation, thus enhancing population differentiation more strongly for some of the Drosophila species. The population structure of each Drosophila species in East and Southeast Asia has been influenced by past geographic events.

The phylogeny of the Drosophila virilis species group was reevaluated by analyzing all previously published data sets. These included 1 developmental, 4 morphological, 6 chromosomal, 7 behavioral, and 10 molecular studies that have examined the group in a comparative way. It was concluded that there are four monophyletic clades within the D. virilis species group: (1) the virilis phylad, which includes D. virilis Sturtevant, D. lummei Hackman, D. novamexicana Patterson, D. americana Spencer, and D. texana Patterson; (2) the montana subphylad, which consists of D. montana Stone, Griffen & Patterson, D. lacicola Patterson, D. borealis Patterson, and D. flavomontana Patterson; (3) the littoralis subphylad consisting of D. littoralis Meigen and D. ezoana Takada & Okada; (4) and the monotypic kanekoi subphylad which includes D. kanekoi Watabe & Higuchi. The consensus phylogeny produced by this reanalysis does not support some of the systematic relationships that are currently accepted. The major division within the group, between the virilis phylad and the montana phylad (which consists of the montana, littoralis, and kanekoi subphylads), is found to be unsupported because in some reanalyses the littoralis and kanekoi subphylads cluster with the virilis phylad, and not the montana phylad. Consequently, the relationships among the phylads and subphylads are considered unresolved. The relationships of the virilis phylad are consistent with previous analyses, although the relationships among D. americana , D. texana , and D. novamexicana are considered unresolved based on the character evidence. Within the montana subphylad the only stable relationship appears to be the ancestral position of D. flavomontana relative to the other species in the subphylad.

Diagnostic studies on the relationship between Drosophila willistoni and Nosema kingi revealed that adult D. willistoni can acquire the microsporidian via the oral route from fecal contamination and transovarially. At least 50% of the flies exposed to fecal material from infected flies contained the parasite when examined two or three weeks later. 50–81% of the offspring which emerged from eggs laid by parasitized females were infected with N. kingi 14–21 days later. Infectivity experiments using other drosophilids indicated N. kingi infections can be transmitted to D. sturtevanti Duda, D. melanogaster Meigen, D. persimilis Dobzhansky and Epling, D. pseudoobscura Frolowa, D. virilis Sturtevant, D. simulans Sturtevant, and D. ananassae Doleshall without morphological changes occurring in the stages of the parasite and without changes of behavioural patterns in these experimental hosts.

Drosophila affinis Sturtevant, D. quinaria Loew, D. putrida Sturt., D. robusta Sturt., D. tripunctata Loew, and D. immigrans Sturt. are the six native species most commonly encountered in north central Indiana, while D. melanogaster Meigen, D. hydei Sturt., and D. busckii Coquillett are introduced species which frequently attain large summer populations. Summer populations of the native species originate in deciduous woodlands, and during periods of population maxima in June the more prevalent species are widely dispersed through all of the major types of terrestrial habitats. Summer populations of the introduced species originate in proximity to human settlements and likewise disperse through a variety of habitats during periods of population increase, occurring with the native species in diverse situations in July but not achieving peak numbers until August. The species which infest tomatoes are widely, if thinly, dispersed at the time the crop ripens, and there is little expectation that preseason control efforts would be practicable. Despite disparate climatic conditions during the summers of 1958 and 1959, population developments in tomato fields were strikingly similar, thus indicating little correlation between normal weather extremes and population development. D. melanogaster is recognized as the principal species causing contamination of tomato products. Experimental evidence on comparative fecundity, developmental rates, and ovipositional behavior were obtained to explain the consistent prevalence of this species. Studies of diurnal activity and spatial distribution suggest that these facets of behavior are controlled principally by responses to atmospheric moisture. Adult flies were found to inhabit a space, only a few inches in height, directly above the soil surface. The micro environment provided by the foliage and fruit of the tomato plant does not require the insects to follow the pattern of peak activity at dawn and dusk often ascribed to Drosophila .

The natural population of a site in Fusagasuga, Colombia, was sampled weekly from March 1964 to December 1965, and weights of the collected adult Drosophila were determined. D. melanogaster Meigen, D. immigrans Sturtevant, D. cardini Sturtevant, and D. capricorni Dobzhansky & Paven were the most abundant species. The total number collected of D. immigrans, D. bandcirantorum Dobzhansky& Pavan, the D, tripunctata Loew group, and 77. griscolineata Duda was higher after rainy months than after dry months. This correlation did not hold for D. mclanogaster or D. cardini . The average weight of female D. melanogaster and D. immigrans collected during rainy months was higher than that of females collected during dry months. However, the reverse was true for D. cardini . A greater variety of species of Drosophila was taken at Fusagasuga than in a previous study at a higher altitude in Colombia.