Vairimorpha (formerly Nosema) apis and V. ceranae are microsporidian pathogens that are of concern for managed honey bee colonies. Multiple treatments have been proposed to be effective in reducing the prevalence and intensity of Vairimorpha spp. infections. Here, we test the efficacy of these products in one lab-based experiment and three field experiments. In the lab experiment, we found no reductions in Vairimorpha spp. prevalence (proportion of individuals infected with Vairimorpha spp.) or intensity (number of Vairimorpha spp. spores per individual), but we did find a decrease in honey bee survival after treatment with Fumagilin-B, Honey-B-Healthy®, and Nozevit Plus. The first field experiment showed increased Vairimorpha spp. intensity in colonies treated with Fumagilin-B and HiveAlive® compared to a negative control (sucrose syrup alone). The second field experiment showed a weak reduction in Vairimorpha spp. intensity after 3 weeks post treatment with Fumagilin-B compared to Nozevit. However, Vairimorpha spp. intensity returned to levels comparable to those of other treatment groups after 5 weeks post treatment and remained similar to those of other groups for the duration of the experiment. The final field trial showed no positive or negative effects of treatment with Fumagilin-B or Nosevit on Vairimorpha spp. prevalence or intensity. These findings raise questions regarding the efficacy of the products currently being used by beekeepers to control Vairimorpha spp. We argue that the observed reduction of Vairimorpha spp. is more likely relevant to the phenology of spore prevalence and intensity in honey bee colonies than to chemical treatment.

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.

There is growing appreciation for the role that parasites have in ecosystems and food webs, though the possibility that they could improve an ecosystem service has never been considered. In forest ecosystems, fallen trees naturally decay over time and slowly return their nutrients to the soil. Beetles in the family Passalidae play a key role by excavating tunnels and consuming wood from these logs, thereby breaking down the wood into smaller debris. In the eastern United States, the horned passalus (Odontotaenius disjunctus) is host to a naturally occurring nematode, Chondronema passali, which appears to cause little harm to the beetles. We suspected this was due to compensatory food consumption by parasitized individuals, which we tested here. We collected and housed 113 adult beetles in individual containers with wood for three months, then determined the amount of wood each beetle had processed into fine debris and frass. We then assessed beetles for C. passali and compared wood processing rates between parasitized and non-parasitized groups. Results showed the average daily processing rate of parasitized beetles ( x ¼ 0.77 g d 21 ) was 15% greater than that of unparasitized ones ( x ¼ 0.67 g d 21 ). Parasitized beetles were 6% larger, and this may explain some of this pattern, though the effect of parasitism was still significant in our analysis. By extrapolating the daily rates, we estimate that 10 adult beetles without nematodes would break down approximately 2.4 kg of wood in a single year, while a group of 10 parasitized beetles would break down 2.8 kg. While our data are consistent with the idea of compensatory feeding, because these results are based on natural infections, we cannot rule out the possibility that beetles with heightened wood consumption are simply more likely to acquire the parasite. At an ecosystem level, it may not matter which is the case; parasitized beetles provide a more effective ecosystem service.

The rigours of the daily lives of insects sometimes lead to minor injuries and wounds, which must be healed to avoid entry of pathogens and to resume normal function. Such healing requires energy, which must be diverted from other bodily reserves. What happens if energy reserves are already low, as would occur in individuals coping with internal parasites? This question is addressed in the presemt study, using horned passalus beetles (Odontotaenius disjunctus) and their naturally-occurring nematode Chondronema passali. Oxygen consumption rates are tested at rest, as well as after an experimental wound is applied, to evaluate energy requirements of wound-healing in parasitized and nonparasitized hosts. Furthermore, wound-healing rates are visually tracked with a numerical scoring system to directly measure the cost of parasitism on healing. At rest, parasitized beetles show no elevation in respiration (oxygen consumption). After wounding, the oxygen consumption of parasitized beetles is 10% higher than that in nonparasitized beetles. Beetles with moderate-to heavy worm burdens have slower healing than those with few or no nematodes. These results show that this parasite carries little cost to the host during day-to-day activities, whereas, during times of immediate energy demand, there is a cost; hosts require more energy to repair wounds, and the wounds take longer to close. This conclusion leads to the question of whether this parasite is truly benign, and how many other apparently benign parasites, in insects or other animals, have similar 'hidden' effects.

Numerous studies have documented the negative effects of neonicotinoids on bees; it remains crucial to examine how neonicotinoids affect other non‐target nectar‐feeding insects, such as the monarch butterfly, Danaus plexippus. Wildflowers growing near agricultural areas can be contaminated with neonicotinoids that affect survival or cause sublethal changes to behaviours of nectar‐feeding insects. Nectar residues of imidacloprid and clothianidin found in milkweeds and wildflowers adjacent to agricultural field range from 0 to 72.8 ng/mL. At field‐relevant doses, two neonicotinoids (imidacloprid and clothianidin) were studied for their effects on adult monarch survival, reproduction, flight and behaviour. First, we fed adult monarchs artificial nectar solutions ranging from 15 to 386 ng/mL of imidacloprid and 19 to 531 ng/mL of clothianidin. Neonicotinoid ingestion slightly reduced monarch reproduction but had no significant effects on survival, weight change, or activity levels. Second, we fed monarchs higher clothianidin doses (909 and 4030 ng/mL), that exceed field‐relevant levels by 22 and 99 times. These higher doses reduced monarch nectar consumption, survival, flight performance and reaction time in response to a drop test. Results show that adult monarchs tolerate field‐relevant doses as high as 54 ng/mL for imidacloprid and 75 ng/mL for clothianidin, with minimal lethal or sub‐lethal effects until much higher doses are supplied. We conclude that adult monarchs are more tolerant of ingested clothianidin and imidacloprid than indicated by previous research.