Garlic mustard (Alliaria petiolata), an invasive plant of the North American forest understory, is the target of importation biological control programs in both the United States and Canada. After host range testing was completed in the US, a garlic mustard rosette crown-mining weevil from Europe, Ceutorhynchus scrobicollis, was released in Canada in 2018 and has recently been approved for release in the United States. We defined temperature-dependent thresholds for C. scrobicollis oviposition behaviour and cumulative thermal units required for F1 development within garlic mustard rosettes. These thermal requirements of C. scrobicollis were then used to inform a degree-day model to predict the potential geographic distribution of the imported biological control agent in the Great Lakes region of North America. We found that Cumulative Degree Days accumulated during the rosette seasons in 2020 through 2024 were sufficient for C. scrobicollis parasitism of garlic mustard rosettes to take place in Southern Ontario, as well as the central and upper Midwest and Northeast regions of the United States.

1. The composition of the necrobiome community in the Galapagos Islands is poorly understood, and nothing is known about the dynamics between endemic species and those introduced through human activity.2. To determine the composition of the carrion fly community, specifically members of the families Muscidae, Calliphoridae and Sarcophagidae, we deployed four kinds of carrion bait traps during the cool and hot seasons at two lowland and two highland sites on Santa Cruz Island within the Galapagos archipelago. We also conducted a laboratory experiment to assess resource competition between fly species encountered in the baiting study.3. Of the eight fly species found in our baited traps, all were introduced except for the endemic sarcophagid, Sarothromyiops dasycnemis. Four endemic and one native carrion-feeding species that had been previously recorded on this island were not found. The introduced sarcophagid, Peckia chrysostoma, was the most abundant fly species, comprising over half of the collected specimens, and it was highly dominant at the lowland sites. The endemic species, S. dasycnemis, was only recorded at the lowland sites during the hot season. On the other hand, the calliphorid species were dominant at the highland sites.4. Experiments demonstrated that P. chrysostoma is a strong competitor against other carrion fly species in the Galapagos necrobiome, including the endemic S. dasycnemis.5. A comparison of our data with historical records, combined with the results of our laboratory study, leads to the conclusion that introduced carrion fly species, such as P. chrysostoma, represent a threat to endemic carrion fly species, such as S. dasycnemis.6. Three parasitoid species were reared from 19% of the collected fly puparia. Two of these species attacked fly larvae (Brachymeria podagrica and Aphaereta sp.), whereas one species attacked fly puparia (Exoristobia sp.)7. We discuss our results in light of the possibility of the purposeful introduction of a parasitoid as a biological control agent against the avian vampire fly (Philornis downsi; Diptera: Muscidae) in Galapagos.

Many parasites of seasonally available hosts must persist through times of the year when hosts are unavailable. In tropical environments, host availability is often linked to rainfall, and adaptations of parasites to dry periods remain understudied. The bird-parasitic fly Philornis downsi has invaded the Galapagos Islands and is causing high mortality of Darwin’s finches and other bird species, and the mechanisms by which it was able to invade the islands are of great interest to conservationists. In the dry lowlands, this fly persists over a seven-month cool season when availability of hosts is very limited. We tested the hypothesis that adult flies could survive from one bird-breeding season until the next by using a pterin-based age-grading method to estimate the age of P. downsi captured during and between bird-breeding seasons. This study showed that significantly older flies were present towards the end of the cool season, with ~ 5% of captured females exhibiting estimated ages greater than seven months. However, younger flies also occurred during the cool season suggesting that some fly reproduction occurs when host availability is low. We discuss the possible ecological mechanisms that could allow for such a mixed strategy.

Quantitative food web analyses can provide insights into the specificity of consumers such as herbivores, parasites and parasitoids. Understanding such patterns can be useful in forecasting the potential benefits and risks of biological control agents being considered for introduction against invasive species. The avian vampire fly, Philornis downsi (Diptera: Muscidae), is a neotropical bird parasite that is invasive in the Galapagos Islands, where it is causing substantial mortality of endemic bird species. We used a novel in-field experimental food web approach within the native range of P. downsi in Ecuador to test the hypotheses that pupal parasitoids known to attack P. downsi specialize on members of the genus Philornis, which occur only in bird nests. We deployed pupae of non-Philornis fly species adjacent to bird nests to assess specificity of the parasitoids and used two indices to assess specificity: Resource Range (RR), which evaluates the breadth of host use, and Pair Difference Index (PDI), which evaluates interaction strength. The results revealed very strong compartmentalization within the guild of pupal fly parasitoids, with four species attacking only Philornis spp. Both specificity indices indicated significant levels of specificity towards the genus Philornis for two of these species: Conura annulifera and Trichopria sp. novus. We also assessed the specificity of the two dominant Philornis species attacking 11 bird species and preference of the two dominant parasitoid species for bird species. Although there was some significant preference for particular bird species by the Philornis spp., there was no indication that this drove specificity patterns by the parasitoids. Policy implications. Our results confirm previous laboratory studies indicating specificity by C. annulifera and support the hypothesis that this species would produce few, if any, nontarget impacts if released into Galapagos to suppress populations of the P. downsi. These results can inform an environmental risk assessment framework to guide governmental agencies in deliberation on potential field releases of parasitoids in the Galapagos Islands.

The Avian Vampire Fly, Philornis downsi, has invaded the Galapagos Islands, where it causes high mortality of endemic and native landbird species, including most species of Darwin's finches. Control methods are under development, but key information is missing about the reproductive biology of P. downsi and the behavior of flies in and near nests of their hosts. We used external and internal nest cameras to record the behavior of P. downsi adults within and outside nests of the Galapagos Flycatcher, Myiarchus magnirostris, throughout all stages of the nesting cycle. These recordings showed that P. downsi visited flycatcher nests throughout the day with higher fly activity during the nestling phase during vespertine hours. The observations also revealed that multiple P. downsi individuals can visit nests concurrently, and that there are some interactions among these flies within the nest. Fly visitation to nests occurred significantly more often while parent birds were away from the nest than in the nest, and this timing appears to be a strategy to avoid predation by parent birds. We report fly mating behavior outside the nest but not in the nest cavity. We discuss the relevance of these findings for the adaptive forces shaping P. downsi life history strategies as well as rearing and control measures.

The neotropical parasitoid Conura annulifera (Walker) (Hymenoptera: Chalcididae) is known to parasitize bird-parasitic flies in the genus Philornis (Diptera: Muscidae) including P. downsi (Dodge and Aitken), a species that has invaded the Galapagos islands and is negatively impacting populations of Darwin's finches. We report here some aspects of the life history, field ecology, and host specificity of C. annulifera. We collected puparia of four Philornis species in 13 bird nests during 2015 and 2016 in western mainland Ecuador and found that C. annulifera and three other parasitoid species emerged from those puparia. This is the first record of C. annulifera in Ecuador. Rearing records and dissections of parasitized puparia revealed that C. annulifera is a solitary pupal ectoparasitoid, placing its eggs in the gap between host pupa and puparium. Laboratory studies of host specificity involving P. downsi and pupae from five other dipteran, three lepidopteran, and one hymenopteran species found that C. annulifera only produced progeny when presented with P. downsi pupae. Pupae of P. downsi that had been exposed to C. annulifera also failed to emerge more often than expected by chance compared with no-parasitoid controls, suggesting that the parasitoids can cause developmental mortality through means other than successful parasitism. These studies constitute the first steps in evaluating C. annulifera as a potential biological control agent of P. downsi in the Galapagos Islands.