Browsing by Author "Heimpel, George E"

Now showing 1 - 6 of 6
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    Biological control benefit-risk analysis; Heimpel et al. Ecological Applications
    (2024-05-06) Heimpel, George E; Abram, Paul K; Causton, Charlotte E; Celis, Sabrina L; Coll, Moshe; Hardy, Ian CW; Mangel, Marc; Mills, Nicholas J; Segoli, Michal; heimp001@umn.edu; Heimpel, George E; University of Minnesota Heimpel Laboratory
    The release of biological control agents has been an important means of controlling invasive species for over 150 years. While these releases have led to the sustainable control of over 250 invasive pest and weed species worldwide, a minority have caused environmental harm. A growing recognition of the risks of biological control led to a focus on risk assessment beginning in the 1990s along with a precipitous decline in releases. While this new focus greatly improved the safety of biological control, it came at the cost of lost opportunities to solve environmental problems associated with invasive species. A framework that incorporates benefits and risks of biological control is thus needed to understand the net environmental effects of biological control releases. We introduce such a framework, using native biodiversity as the common currency for both benefits and risks. The model is based on interactions among four categories of organisms: (i) the biological control agent, (ii) the invasive species (pest or weed) targeted by the agent, (iii) one or more native species that stand to benefit from the control of the target species, and (iv) one or more native species that are at risk of being harmed by the released biological control agent. Conservation values of the potentially benefited and harmed native species are incorporated as well, and they are weighted according to three axes: vulnerability to extinction, the ecosystem services provided, and cultural significance. Further, we incorporate the potential for indirect risks to native species, which we consider will result mainly from the ecological process of agent enrichment that may occur if the agent exploits but does not control the target pest or weed. We illustrate the use of this framework by retrospectively analyzing the release of the vedalia beetle, Novius (= Rodolia) cardinalis, to control the cottony cushion scale, Icerya purchasi, in the Galapagos Islands. While the framework is particularly adaptable to biological control releases in natural areas, it can also be used in managed settings, where biological control protects native species through the reduction of pesticide use.
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    Bulgarella et al. Philornis Pterin Data
    (2022-01-12) Bulgarella, M; Heimpel, George E; Lincango, MP; Lahuatte, PF; Oliver, JD; Cahuana, A; Ramírez, IE; Sage, R; Colwitz, AJ; Freund, DA; Miksanek, JR; Moon, RD; Causton, CE; heimp001@umn.edu; Heimpel, George E; University of Minnesota, Dept. of Entomology, Heimpel Lab
    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 successfully 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 reproduction occurs when host availability is low. We discuss the possible ecological mechanisms that could allow for a such a mixed strategy.
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    Data set for the publication "Specificity within bird-parasite-parasitoid food webs: a novel approach for evaluating potential biological control agents of the avian vampire fly"
    (2022-04-27) Ramirez, Ismael E; Causton, Charlotte E; Gutierrez, George A; Mosquera, Denis A; Piedrahita, Paolo; Heimpel, George E; ramir238@umn.edu; Ramirez, Ismael E
    1. 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. 2. 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.
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    Data set for the publication 'Invasive fly species displaces natives in Galapagos with implications for biological control risk assessment'
    (2023-05-10) Ramirez, Ismael E; Yar, Joselyn; Sinclair, Bradley J; Torres, Ana K; Causton, Charlotte E; Heimpel, George E; ramir238@umn.edu; Ramirez, Ismael E; Univeristy of Minnesota Department of Entomology
    The composition and interactions of carrion flies in the Galapagos Islands is poorly understood, especially when focusing on competition between introduced and endemic fly species. We aimed to assess such composition and interactions by deploying carrion bait traps during the cool and hot seasons, and an experimental approach in a controlled setting was used to investigate interspecific competition among them. Of the eight fly species found in our baited traps, all were introduced except for the endemic sarcophagid, Sarothromyiops dasycnemis (Thomson), and a number of endemic species expected to be encountered were not found. The introduced sarcophagid, Peckia chrysostoma (Wiedemann) was the most abundant fly species found overall, comprising over half of the collected specimens. Most fly species exhibited some level of habitat preference. We conducted a laboratory experiment on resource competition between P. chrysostoma and a subset of the fly species encountered in the baiting study. The results demonstrated that P. chrysostoma is a strong competitor against other carrion fly species in the Galapagos necrobiome, including the endemic S. dasycnemis. A comparison of our data to historical records of fly abundance in Galapagos, 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. Three parasitoid species were reared from the puparia collected, two that attacked fly larvae (Brachymeria podagrica and Aphaereta sp.) and one that attacked puparia (Exoristobia sp.). We discuss our results in light of the possibility of the purposeful introduction of a hymenopteran parasitoid as a biological control agent against the avian vampire fly (Philornis downsi Dodge & Aitken) in Galapagos.
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    Mind the Gap: the evolution of oviposition site and specialisation in the parasitoid superfamily Chalcidoidea
    (2018-03-05) Boulton, Rebecca A; Heimpel, George E; rebeccaboulton87@googlemail.com; Boulton, Rebecca A
    Parasitoid wasps have contributed significantly to our understanding of ecological specialisation and the evolution of traits linked to host range. Oviposition site is one such trait. Endoparasitoids deposit their eggs inside the host body and tend to be more highly specialised than ectoparasitoids (which lay eggs externally) because they must develop specific strategies to overcome host immune defences. Intermediate to endo- and ectoparasitism is a strategy that we call ‘gap laying’. Gap-laying parasitoids deposit their eggs between the hard outer puparium and the larva of dipteran hosts. This behaviour has received less empirical attention than endo- and ectoparasitism but has important implications for the evolution of specialisation. Using a phylogenetically controlled comparative approach we find that gap-laying species in the hymenopteran superfamily Chalcidoidea exhibit numeric host ranges intermediate to endo- and ectoparasitoids, but these groups exploit a similarly taxonomically related range of hosts. We found that gap-laying can arise from ectoparasitism or endoparasitism, but once it evolves it shows patterns consistent with an evolutionary dead-end compared to other strategies. The results of this study demonstrate how oviposition site, beyond the normal endo-ectoparasitoid dichotomy, influences host specificity, shedding light on the causes and consequences of ecological specialisation in the parasitic Hymenoptera.
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    Soybean Aphid and Aphelinus certus Development (2017–2019)
    (2019-05-24) Miksanek, James Rudolph; Heimpel, George E; miks0007@umn.edu; Miksanek, James R; University of Minnesota Department of Entomology