More Like this

1. Does the Presence of the Biological Control Agent, Hypena opulenta (Lepidoptera: Erebidae) on Swallow-Worts Deter Monarch Oviposition?

   https://doi.org/10.1093/ee/nvab121  

   Alred, Brianna ; Haan, Nathan ; Landis, Douglas A ; Szűcs, Marianna ( November 2021 , Environmental Entomology)

   Schmidt-Jeffris, Rebecca (Ed.)

   Abstract Invasive black and pale swallow-worts (Vincetoxicum nigrum (L.) Moench, and Vincetoxicum rossicum Kelopow), which are related to milkweeds, can act as ecological traps for monarch butterflies (Danaus plexippus L. (Lepidoptera: Nymphalidae)) as they lay eggs on them that fail to develop. A recently approved biological control agent against swallow-worts, Hypena opulenta Christoph, occupies the same feeding guild on swallow-worts as monarch larvae and could be perceived as a competitor to monarchs. We tested how the presence of this defoliating moth on swallow-worts may influence monarch host selection. In a two-year field experiment, we placed pale swallow-wort plants that were either infested with H. opulenta or noninfested as well as common milkweed (Asclepias syriaca L.), into monarch habitats to assess oviposition rates. In the laboratory, monarchs were either given a choice or not between milkweeds and black swallow-worts with or without H. opulenta. While monarchs strongly preferred common milkweed in the field, up to 25% of the eggs we observed were laid on pale swallow-wort, without preference for swallow-wort with (10.7%) or without (14.3%) H. opulenta. In laboratory choice and no-choice tests, monarchs did not lay any eggs on black swallow-wort, likely because of the long-term laboratory rearing on common milkweeds. Our results confirm that pale swallow-wort may act as an oviposition sink to monarchs in Michigan as well. Since the biological control program is still in its infancy, the nature of interactions between monarchs and H. opulenta may change as the biocontrol agent becomes more widespread. 

   more » « less
2. Host Plant Species Mediates Impact of Neonicotinoid Exposure to Monarch Butterflies

   https://doi.org/10.3390/insects12110999  

   Prouty, Cody ; Barriga, Paola ; Davis, Andrew K. ; Krischik, Vera ; Altizer, Sonia ( November 2021 , Insects)

   Neonicotinoids are the most widely used insecticides in North America. Numerous studies document the negative effects of neonicotinoids on bees, and it remains crucial to demonstrate if neonicotinoids affect other non-target insects, such as butterflies. Here we examine how two neonicotinoids (imidacloprid and clothianidin) affect the development, survival, and flight of monarch butterflies, and how these chemicals interact with the monarch’s milkweed host plant. We first fed caterpillars field-relevant low doses (0.075 and 0.225 ng/g) of neonicotinoids applied to milkweed leaves (Asclepias incarnata), and found no significant reductions in larval development rate, pre-adult survival, or adult flight performance. We next fed larvae higher neonicotinoid doses (4–70 ng/g) and reared them on milkweed species known to produce low, moderate, or high levels of secondary toxins (cardenolides). Monarchs exposed to the highest dose of clothianidin (51–70 ng/g) experienced pupal deformity, low survival to eclosion, smaller body size, and weaker adult grip strength. This effect was most evident for monarchs reared on the lowest cardenolide milkweed (A. incarnata), whereas monarchs reared on the high-cardenolide A. curassavica showed no significant reductions in any variable measured. Our results indicate that monarchs are tolerant to low doses of neonicotinoid, and that negative impacts of neonicotinoids depend on host plant type. Plant toxins may confer protective effects or leaf physical properties may affect chemical retention. Although neonicotinoid residues are ubiquitous on milkweeds in agricultural and ornamental settings, commonly encountered doses below 50 ng/g are unlikely to cause substantial declines in monarch survival or migratory performance. 

   more » « less
3. Transcriptomics of monarch butterflies ( Danaus plexippus ) reveals that toxic host plants alter expression of detoxification genes and down‐regulate a small number of immune genes

   https://doi.org/10.1111/mec.15219  

   Tan, Wen‐Hao ; Acevedo, Tarik ; Harris, Erica V. ; Alcaide, Tiffanie Y. ; Walters, James R. ; Hunter, Mark D. ; Gerardo, Nicole M. ; de Roode, Jacobus C. ( September 2019 , Molecular Ecology)

   Herbivorous insects have evolved many mechanisms to overcome plant chemical defences, including detoxification and sequestration. Herbivores may also use toxic plants to reduce parasite infection. Plant toxins could directly interfere with parasites or could enhance endogenous immunity. Alternatively, plant toxins could favour down‐regulation of endogenous immunity by providing an alternative (exogenous) defence against parasitism. However, studies on genomewide transcriptomic responses to plant defences and the interplay between plant toxicity and parasite infection remain rare. Monarch butterflies (Danaus plexippus) are specialist herbivores of milkweeds (Asclepiasspp.), which contain toxic cardenolides. Monarchs have adapted to cardenolides through multiple resistance mechanisms and can sequester cardenolides to defend against bird predators. In addition, high‐cardenolide milkweeds confer monarch resistance to a specialist protozoan parasite (Ophryocystis elektroscirrha). We used this system to study the interplay between the effects of plant toxicity and parasite infection on global gene expression. We compared transcriptional profiles between parasite‐infected and uninfected monarch larvae reared on two milkweed species. Our results demonstrate that monarch differentially express several hundred genes when feeding onA. curassavicaandA. incarnata, two species that differ substantially in cardenolide concentrations. These differentially expressed genes include genes within multiple families of canonical insect detoxification genes, suggesting that they play a role in monarch toxin resistance and sequestration. Interestingly, we found little transcriptional response to infection. However, parasite growth was reduced in monarchs reared onA. curassavica, and in these monarchs, several immune genes were down‐regulated, consistent with the hypothesis that medicinal plants can reduce reliance on endogenous immunity.

    

   more » « less
4. Impacts of larval host plant species on dispersal traits and free-flight energetics of adult butterflies

   https://doi.org/10.1038/s42003-022-03396-8  

   Pocius, Victoria M. ; Cibotti, Staci ; Ray, Swayamjit ; Ankoma-Darko, Obenewa ; McCartney, Nathaniel B. ; Schilder, Rudolf J. ; Ali, Jared G. ( May 2022 , Communications Biology)

   Animals derive resources from their diet and allocate them to organismal functions such as growth, maintenance, reproduction, and dispersal. How variation in diet quality can affect resource allocation to life-history traits, in particular those important to locomotion and dispersal, is poorly understood. We hypothesize that, particularly for specialist herbivore insects that are in co-evolutionary arms races with host plants, changes in host plant will impact performance. From their coevolutionary arms-race with plants, to a complex migratory life history, Monarch butterflies are among the most iconic insect species worldwide. Population declines initiated international conservation efforts involving the replanting of a variety of milkweed species. However, this practice was implemented with little regard for how diverse defensive chemistry of milkweeds experienced by monarch larvae may affect adult fitness traits. We report that adult flight muscle investment, flight energetics, and maintenance costs depend on the host plant species of larvae, and correlate with concentration of milkweed-derived cardenolides sequestered by adults. Our findings indicate host plant species can impact monarchs by affecting fuel requirements for flight.

    

   more » « less
5. Plant water limitation and its impact on the oviposition preferences of the monarch butterfly (Lepidoptera: Nymphalidae)

   https://doi.org/10.1093/jisesa/iead075  

   Diethelm, Aramee C. ; Kost, Konnor E. ; Pringle, Elizabeth G. ; Hesler, ed., Louis ( August 2023 , Journal of Insect Science)

   Intensifying drought conditions across the western United States due to global climate change are altering plant–insect interactions. Specialist herbivores must find their host plants within a matrix of nonhosts, and thus often rely upon specific plant secondary chemistry for host location and oviposition cues. Climate-induced alterations to plant chemistry could thus affect female selection of larval food plants. Here, we investigated whether host-plant water limitation influenced oviposition preference in a threatened invertebrate: the monarch butterfly (Danaus plexippus). We found that females deposited more eggs on reduced-water than on well-watered narrowleaf milkweed plants (Asclepias fascicularis), but we could not attribute this change to any specific change in plant chemistry. Specialist herbivores, such as the monarch butterfly, which are tightly linked to specific plant cues, may experience shift in preferences under global-change conditions. Understanding oviposition preferences will be important to directing ongoing habitat restoration activities for this declining insect.

    

   more » « less