Microbiota-mediated competition between Drosophila species

Ganaspis individuals parasitizing Drosophila suzukii (Matsumura), a pest of fruit crops, were examined for host use and molecular and morphological differences from those attacking D. lutescens Okada and some other Drosophila species that breed on fermenting fruits. Wild cherry fruits were collected in the suburbs of Tokyo, and drosophilid pupae obtained from these fruits were examined for parasitism. Drosophila suzukii was the only drosophilid species infesting fresh wild cherry fruits, and Ganaspis individuals were the major parasitoids attacking D. suzukii in wild cherry fruits. In parasitism experiments, these Ganaspis individuals parasitized D. suzukii larvae in fresh cherry fruits, but did not parasitize those in Drosophila medium. In addition, they did not parasitize larvae of some other fruit-feeding Drosophila species even when these occurred in fresh cherry fruit. These Ganaspis individuals parasitizing D. suzukii were different from those parasitizing D. lutescens and some other drosophilids in nucleotide sequences of the COI gene, as well as in ITS1 and ITS2. They were also different in forewing and antenna morphology, although they showed some overlap in morphological traits. They are tentatively assigned as the suzukii- and lutescens-associated types of G. xanthopoda Ashmead. In the present field survey, Leptopilina japonica Novkovic & Kimura and some Asobara species were also observed to attack D. suzukii larvae in wild cherry fruit.

BackgroundDengue is a mosquito-borne viral disease endemic to tropical regions, primarily transmitted by Aedes aegypti and Aedes albopictus. Climate-driven temperature changes are altering vector ecology and expanding the geographic range where both species coexist. However, the combined effects of temperature variability and interspecific interactions, particularly the highly competitive larval stage, on mosquito population dynamics and dengue transmission remain poorly understood.MethodsWe developed a deterministic model incorporating temperature-dependent parameters to analyze vector interactions across larval stage, coupled with a Susceptible–Exposed–Infected–Recovered (SEIR) framework for human infection dynamics. We evaluated species invasion capability, population dynamics, and transmission patterns through invasion and coexistence analyses, as well as infection peak assessment. The basic reproductive number (R_0) was derived analytically using the next-generation matrix (NGM) method, while the effective reproductive number (R_t) was computed from numerical simulations to capture dynamic effects of larval competition.ResultsThe invasion analysis showed that larval competition was the central determinant of species outcomes. Under temperature-independent conditions, Aedes albopictus could invade only when the larval pressure exerted by Aedes aegypti (omega _{ae}) was relatively low, while intermediate values produced neutral dynamics, and higher values prevented invasion. Incorporating temperature dependence broadened the parameter space in which invasion was possible, indicating that thermal variation enhances the invasion potential of Aedes albopictus. Coexistence patterns reflected this shift; temperature-independent simulations favored Aedes aegypti dominance, whereas temperature-dependent scenarios led to nearly balanced coexistence between the species. Dengue transmission patterns qualitatively followed these ecological dynamics. Temperature-independent simulations produced smaller peaks in human dengue cases, while temperature-dependent scenarios yielded a larger number of cases. Stronger competition from Aedes albopictus lowered epidemic intensity. The basic reproductive number (R_0) was indirectly modulated by larval competition through its effects on adult mosquito abundance, while the effective reproductive number (R_t) remained higher in temperature-independent settings and decreased substantially under stronger larval competition in temperature-dependent simulations. The purpose of the transmission component of the model is to illustrate how changes in larval competition propagate through the transmission framework, rather than to provide quantitatively validated epidemiological estimates.ConclusionsTemperature significantly influences competitive interactions and dengue transmission dynamics between Ae. aegypti and Ae. albopictus. Temperature-dependent conditions enhance Ae. albopictus invasion and promote coexistence, while Ae. aegypti drives higher infection peaks under favorable thermal conditions. Increased Ae. albopictus competition lowers transmission, particularly in temperature-dependent scenarios; however, situations where both vectors exhibit similar abundances represent the most concerning context. These findings underscore the importance of integrating temperature effects and interspecific competition into vector control strategies in regions such as Colombia, where both species coexist, to effectively mitigate dengue transmission under varying climatic conditions.Graphical abstractSupplementary InformationThe online version contains supplementary material available at 10.1186/s13071-025-07187-y.

1. High competitive ability is believed to be an important characteristic of invasive species. Many animal studies have compared the competitive ability of invasive species with a native species that is being displaced, but few have looked at systems where an invasive species has failed to establish itself. These types of studies are important to determine if competition is relevant not only to invading species but also to the biotic resistance of a community. 2. The thrips species F. occidentalis is a highly invasive pest that has spread from its original range (the western states of the USA) to a worldwide distribution. Despite this, F. occidentalis is largely absent or occurs in low numbers in the eastern states of the USA, where the native F. tritici dominates. It is possible that F. tritici is competitively excluding F. occidentalis from this region. 3. Larval competition between these two thrips species was tested on two known plant hosts, Capsicum annuum (a crop plant), and Raphanus raphanistrum (an invasive weed), using a response surface design with number of larvae surviving as the response variable. The response surface design allowed competition models to be fit to data using maximum likelihood estimation, thus generating quantitative values for interspecific competition. 4. On both plant hosts, the native F. tritici did not experience significant interspecific competition from the invasive F. occidentalis. In contrast, F. occidentalis did experience significant interspecific competition from F. tritici. Competition from F. tritici larvae on F. occidentalis larvae was estimated to be 1.72 times (on C. annuum) and 1.76 times (on R. raphanistrum) the effect of intraspecific competition. The invasive F. occidentalis appears to be competitively excluded by the native F. tritici. 5. This study confirms the importance of competition in the biotic resistance of a community and is one of the few animal studies to not only test for competition in an apparently resistant ecosystem but also to quantify the level of interspecific competition between two animal species.

Abstract. The effects of intraspecific and interspecific larval competition on larval survival, adult size, adult longevity and fecundity were quantified in four species of coexisting Lucilia blowflies: illustris, silvarum, sericata and caesar . There was a general negative effect of increasing density on larval and adult survival, size and fecundity. Additionally, complex species‐specific and frequency‐dependent responses were identified, which were not expected in these biologically and morphologically closely similar species. Lucilia illustris , the numerically dominant species in the natural community, was a superior competitor to L.silvarum at intermediate densities but an inferior competitor at high density. Such nonlinear responses may be related to differences in the life histories and larval behaviour of the species (bigger eggs and more contest‐type outcome of competition in L.silvarum ). We parameterized a model of interspecific competition on a subdivided resource in an attempt to reconcile the conflicting results on larval competitive abilities and the abundances of the species in the field. Using laboratory and field‐estimated parameter values the model predicted coexistence of L.illustris and L.silvarum and the observed numerical dominance of the former species. The average densities of flies in the field are limited to relatively low levels, apparently preventing L.silvarum (the superior competitor at high density) from dominating and excluding L. illustris .

Aedes albopictus (Skuse) and Aedes japonicus (Theobald) are two of the most recent and widespread invasive mosquito species to have become established in the United States. The two species co-occur in water-filled artificial containers, where crowding and limiting resources are likely to promote inter- or intraspecific larval competition. The performance of northern Virginia populations of Ae. japonicus and Ae. albopictus competing as larvae under field conditions was evaluated. Per capita rates of population increase for each species were estimated, and the effects of species composition and larval density were determined. In water-containing cups provided with oak leaves, Ae. albopictus larvae exhibited a competitive advantage over Ae. japonicus as a consequence of higher survivorship, shorter developmental time, and a significantly higher estimated population growth rate under conditions of interspecific competition. Intraspecific competition constrained population performance of Ae. albopictus significantly more than competition with Ae. japonicus. In the context of the Lotka-Volterra model of competition, these findings suggest competitive exclusion of Ae. japonicus in those habitats where this species co-occurs with Ae. albopictus.

When all life stages of Aedes albopictus and A. polynesiensis have been allowed to freely compete in a single cage, such interaction has caused the latter species to be greatly reduced or even exterminated. The experiments described herein were designed to explore whether a similar reduction would occur when only the larval stages of each species were allowed to compete with one another. It was shown that interspecific larval competition caused A. polynesiensis to be eliminated in a relatively short period of time. These results indicate that larval competition plays a major role in the reduction of A. polynesiensis when the 2 species are reared together under laboratory conditions.

(1) This paper investigates the occurrence of larval competition in several domestic species of Drosophila in a fruit and vegetable market. (2) Regular seasonal changes in body size were demonstrated in D. melanogaster Meigen. (3) The heritability of body size in the field was negligible and so the seasonal changes must have been due to the environmental effects of temperature and larval density. (4) Multiple regression analysis was used to separate the effects of temperature from the effects of larval density. Density was found to account for a significant amount of the variation in body size in D. melanogaster. This is evidence of intraspecific competition. (5) Interspecific competition was demonstrated by the fact that the density of D. melanogaster was found to affect the body size of several other species. (6) The coexistence of seven species of Drosophila in the fruit and vegetable market was explained by the partitioning of breeding sites and by the fact that the community may never reach equilibrium.

Ecological interactions among plants, insect herbivores, and parasitoids are pervasive in nature and play important roles in community assembling, but the codiversification of tri-trophic interactions has received less attention. Here we compare pairwise codiversification patterns between a set of 22 fig species, their herbivorous pollinating and galling wasps, and their parasitoids. The parasitoid phylogeny showed significant congruence and more cospeciation events with host insects phylogeny than with host plants. These results suggest that parasitoid phylogeny and speciation is more closely related to their host insects than to their host plants. The pollinating wasps hosted more parasitoid species than gallers and indicated a more intense interspecific competition among parasitoids associated with pollinators. Closer matching and fewer evolutionary host shifts were found between parasitoids and galler hosts than between parasitoids and pollinator hosts. These results suggest that interspecific competition among parasitoids, rather than resource availability of host wasps, is the main driver of the codiversification pattern in this community. Therefore, our study highlights the important role of interspecific competition among high trophic level insects in plant-insect tri-trophic community assembling.

BackgroundAedes aegypti and Aedes albopictus are two globally invasive vectors with similar ecological niches. Encounters between them can result in either competitive exclusion or stable co-existence, but it is unclear what drives these variable outcomes. Larval competition in favor of Ae. albopictus is a main hypothesis for the competitive exclusion of Ae. aegypti observed in some regions. However, the role of oviposition preference in determining the degree of competitive larval interactions in the field is not well understood. In this study, we used a combination of mark-release-recapture methods with ovitraps in the open-field and a semi-field cage to test whether gravid Ae. albopictus seek oviposition sites in response to the presence, species, and density of either conspecific or heterospecific Ae. aegypti larvae in the aquatic habitat. We conducted our study in Medellín, Colombia, where Ae. aegypti is a long-term resident and Ae. albopictus is a recent invader.ResultsIn the open-field and semi-field cage experiments, gravid Ae. albopictus showed strong preference for ovitraps with larvae over those without. They consistently preferred ovitraps with higher density of conspecific (Ae. albopictus) larvae and low density of heterospecific (Ae. aegypti) larvae over traps with no larvae or high density of heterospecific (Ae. aegypti) larvae. In the semi-field cage experiment, traps with low density of Ae. albopictus were not preferred more or less than any other trap, but in the open-field experiment they were preferred over traps without larvae.ConclusionsWe demonstrate, through open-field and semi-field cage experiments, that Ae. albopictus are more attracted to oviposition sites with larvae and that the combination of species and density of larvae influence attraction. This demonstrated preference could increase interspecific larval competition as Ae. albopictus actively seek containers with conspecific and heterospecific larvae. Any resulting competition with Ae. aegypti may favor one species over the other and alter the distribution or abundance of both. Because these species vary in vectorial capacity and insecticide resistance, effects of interspecific competition could ultimately impact arbovirus transmission rates and the success of vector control efforts.

Maternal effects can occur whenever variation among maternal phenotypes provides an additional (usually nongenetic) source of variation among offspring phenotypes (Mousseau and Dingle 1991). For many insects, an important maternal character is the choice of an oviposition site. If juvenile stages are fairly sedentary, a female’s egg-laying preferences can largely or completely determine the quality of her offspring’s environment, sometimes for the duration of its development. Oviposition choices influence a larva’s food quality and its susceptibility to natural enemies or abiotic stresses, as well as its probability of experiencing intra or interspecific competition (Mitchell 1983; Thompson 1983). Here I consider maternal influences on the degree of competition among offspring in insects. I describe genetic and nongenetic sources of variation in egg-laying behavior and discuss how genetic variation in oviposition behavior can persist in populations despite its apparent link to fitness.

Achiasmy and sex chromosome evolution

The spotted-wing drosophila (Drosophila suzukii), a highly invasive agricultural pest, poses significant challenges to fruit production worldwide. Traditional chemical control methods are costly and raise concerns about resistance and environmental sustainability. The Heterospecific Sterile Insect Technique (h-SIT) has emerged as a promising alternative. Sterile heterospecific males (Drosophila melanogaster) can be used to suppress D. suzukii populations through reproductive interference, primarily mediated by post-zygotic isolation mechanisms. Although this approach ensures the absence of viable offspring from heterospecific matings, male sterilization through irradiation remains essential. It prevents unintended ecological effects from D. melanogaster proliferation in the release area and allows for safe large-scale implementation. Therefore, determining an optimal irradiation dose is critical for achieving high levels of male sterility and maintaining biological quality and mating performance. This study aimed to determine the optimal irradiation dose by assessing induced sterility in D. melanogaster males exposed to gamma ray doses ranging from 80-180 Gy. Subsequently, the longevity and the time spent by irradiated D. melanogaster males courting D. suzukii females were also assessed. Results showed a significant dose-dependent increase in induced sterility, with near-complete sterility at 180 Gy. However, longevity decreased with increasing doses, with males irradiated at 160-180 Gy showing a lifespan reduction of up to 50 days compared to controls. Regardless of the irradiation dose received, D. melanogaster males retained their courtship ability toward D. suzukii females, although males exposed to 160 Gy exhibited reduced courtship activity. These findings showed that, among the tested doses, 80 Gy was the most effective in preserving male longevity and mating performance, significantly reducing fertility, while 180 Gy induced the highest sterility. The potential lifespan and courtship behavior trade-offs warrant further evaluation. Future studies should evaluate field performance to refine the balance between sterility, longevity, and mating performance for effective D. suzukii population suppression.

Ripening stages and volatile compounds present in strawberry fruits are involved in the oviposition choice of Drosophila suzukii (Diptera: Drosophilidae)

Effects of elevated CO2 (twice ambient vs. ambient) and Bt Cry1Ac transgene (Bt cotton cv. 33B vs. its nontransgenic parental line cv. DP5415) on the interspecific competition between two ecologically similar species of cotton aphid Aphis gossypii and whitefly biotype-Q Bemisia tabaci were studied in open-top chambers. The results indicated that elevated CO2 and Bt cotton both affected the population abundances of A. gossypii and biotype-Q B. tabaci when introduced solely (i.e., without interspecific competition) or two species coexisted (i.e., with interspecific competition). Compared with ambient CO2, elevated CO2 increased the population abundances of A. gossypii and biotype-Q B. tabaci as fed on Bt and nontransgenic cotton on 45 (i.e., seedling stage) and 60 (i.e., flowering stage) days after planting (DAP), but only significantly enhanced aphid abundance without interspecific competition on the 45-DAP nontransgenic cotton and 60-DAP Bt cotton, and significantly increased whitefly abundance with interspecific competition on the 45-DAP Bt cotton and 60-DAP nontransgenic cotton. In addition, compared with nontransgenic cotton at elevated CO2, Bt cotton significantly reduced biotype-Q B. tabaci abundances without and with interspecific competition during seedling and flowering stage, while only significantly decreasing A. gossypii abundances without interspecific competition during the seedling stage. When the two insect species coexisted, the proportions of biotype-Q B. tabaci were significantly higher than those of A. gossypii on Bt and nontransgenic cotton at the same CO2 levels, and elevated CO2 only significantly increased the percentages of biotype-Q B. tabaci and significantly reduced the proportions of A. gossypii on seedling and flowering nontransgenic cotton. Therefore, the effects of elevated CO2 were favorable for biotype-Q B. tabaci to out-compete A. gossypii under the predicted global climate change.

The mechanisms allowing the widespread invasive pest Drosophila suzukii to survive from early spring until the availability of the first fruit crops are still unclear. Seasonal biology and population dynamics of D. suzukii were investigated in order to better understand the contribution of the early spring hosts to the infestation of the first fruit crops of the season. We identified hosts available to D. suzukii in early spring and assessed their suitability for the pest oviposition and reproductive success under field and laboratory conditions. The natural infestation rate of one of these hosts, Aucuba japonica, was assessed over springtime and the morphology of the flies that emerged from infested A. japonica fruits was characterized under field conditions. Then, these findings were correlated with long-term monitoring data on seasonal reproductive biology and morphology of the pest, using a cumulative degree-days (DD) analysis. Field sampling revealed that overwintered D. suzukii females were physiologically able to lay eggs at 87 DD which coincided with the detection of the first infested early spring hosts. The latter were continuously and increasingly infested by D. suzukii eggs in nature from early spring until the end of May, in particular Aucuba japonica. Individuals emerged from most of these hosts were characterized by a poor fitness and a rather low success of emergence. In the field, only few summer morphs emerged from naturally infested A. japonica fruits around the end of May-beginning of June. However, field monitoring in orchards revealed that D. suzukii individuals consisted solely of winter morphs until mid-June. These observations indicate that overwintered D. suzukii females are the predominant source for the infestations in the first available fruit crops of the season. We discuss these findings in the context of possible pest control strategies.