Fungicide ingestion reduces net energy gain and microbiome diversity of the solitary mason bee

Fungicides are frequently used during tree fruit bloom and can threaten insect pollinators. However, little is known about how non-honey bee pollinators such as the solitary bee, Osmia cornifrons, respond to contact and systemic fungicides commonly used in apple production during bloom. This knowledge gap limits regulatory decisions that determine safe concentrations and timing for fungicide spraying. We evaluated the effects of two contact fungicides (captan and mancozeb) and four translaminar/plant systemic fungicides (cyprodinil, myclobutanil, penthiopyrad, and trifloxystrobin) on larval weight gain, survival, sex ratio, and bacterial diversity. This assessment was carried out using chronic oral ingestion bioassays where pollen provisions were treated with three doses based on the currently recommended field use dose (1X), half dose (0.5X), and low dose (0.1X). Mancozeb and penthiopyrad significantly reduced larval weight and survival at all doses. We then sequenced the 16S gene to characterize the larvae bacteriome of mancozeb, the fungicide that caused the highest mortality. We found that larvae fed on mancozeb-treated pollen carried significantly lower bacterial diversity and abundance. Our laboratory results suggest that some of these fungicides can be particularly harmful to the health of O. cornifrons when sprayed during bloom. This information is relevant for future management decisions about the sustainable use of fruit tree crop protection products and informing regulatory processes that aim to protect pollinators.

Chemical footprints mediate habitat selection in co-occurring aphids

Habitat selection is a critical process that shapes the spatial distribution of species at local and regional scales. The mechanisms underlying habitat preference rely on environmental factors, species traits, and ecological interactions with other species. Here, we examined spatial segregation between two co-occurring aphid species (Rhopalosiphum maidis and R. padi) on wheat plants. We hypothesized that spatial segregation between these aphid species was mediated by aphid cuticular compounds left as chemical “footprints” on plant surfaces. Combining field and laboratory experiments, we first examined how plant microsites alter fitness by measuring the fecundity of each species. Next, we tested whether intra- and interspecific pre-inhabitation modified habitat selection in both aphid species. Both aphid species preferred and exhibited higher fecundity on wheat stems versus leaves. Laboratory trials showed that R. maidis pre-inhabitation altered R. padi spatial preference. By gas chromatography-mass spectrometry analysis and bioassays testing the effects of aphid density and footprint extracts, we found a density-dependent response, with R. padi avoiding locations previously inhabited by R. maidis. The chemical analysis of footprint crude extracts revealed a highly abundant compound, 1-hexacosanol, and when presented in the synthetic form, also elicited R. padi displacement. Altogether, it indicated that R. maidis footprints altered R. padi habitat selection with cuticular compounds playing a relevant role in the habitat selection process in co-occurring aphid species.

Fungal infections lead to shifts in thermal tolerance and voluntary exposure to extreme temperatures in both prey and predator insects

Pathogens can modify many aspects of host behavior or physiology with cascading impacts across trophic levels in terrestrial food webs. These changes include thermal tolerance of hosts, however the effects of fungal infections on thermal tolerances and behavioral responses to extreme temperatures (ET) across trophic levels have rarely been studied. We examined how a fungal pathogen, Beauveria bassiana, affects upper and lower thermal tolerance, and behavior of an herbivorous insect, Acyrthosiphon pisum, and its predator beetle, Hippodamia convergens. We compared changes in thermal tolerance limits (CTMin and CTMax), thermal boldness (voluntary exposure to ET), energetic cost (ATP) posed by each response (thermal tolerance and boldness) between healthy insects and insects infected with two fungal loads. Fungal infection reduced CTMax of both aphids and beetles, as well as CTMin of beetles. Fungal infection modified the tendency, or boldness, of aphids and predator beetles to cross either warm or cold ET zones (ETZ). ATP levels increased with pathogen infection in both insect species, and the highest ATP levels were found in individuals that crossed cold ETZ. Fungal infection narrowed the thermal tolerance range and inhibited thermal boldness behaviors to cross ET. As environmental temperatures rise, response to thermal stress will be asymmetric among members of a food web at different trophic levels, which may have implications for predator-prey interactions, food web structures, and species distributions.

Improving the Phenotypic Properties of the Ceratitis capitata (Diptera: Tephritidae) Temperature-Sensitive Lethal Genetic Sexing Strain in Support of Sterile Insect Technique Applications

The genetic sexing strain (GSS) of the Mediterranean fruit fly (Ceratitis capitata (Wiedemann)) Vienna 8D53- is based on a male-linked translocation system and uses two selectable markers for male-only production, the white pupae (wp) and the temperature sensitivity lethal (tsl) genes. In this GSS, males emerge from brown pupae and are resistant to high temperatures while females emerge from white pupae, are sensitive to high temperatures. However, double homozygous females (wp tsl/wp tsl) exhibit a slower development rate compared to heterozygous males (wp+tsl+/wp tsl) during the larval stage, which was attributed to the pleiotropic effects of the tsl gene. We present the first evidence that this slower development is due to a different gene, here namely slow development (sd), which is closely linked to the tsl gene. Taking advantage of recombination phenomena between the two loci, we report the isolation of a novel temperature sensitivity lethal strain using the wp mutation as a morphological marker, which showed faster development (wp tsl FD) during the larval stage and increased in its temperature sensitivity compared with the normal tsl strain. Moreover, the introgression of this novel wp tsl FD combined trait into the Vienna 8D53- GSS, resulted in a novel Vienna 8D53- FD GSS, where females showed differences in the thermal sensibility, larval development speed, and productivity profiles. The modification of these traits and their impact on the mass rearing of the GSS for sterile insect technique applications are discussed.

A Method for a Long-Term Marking of Spotted Lanternfly (Hemiptera: Fulgoridae) Using a Stable Isotope of Nitrogen

Developing a lifelong marking method for Lycorma delicatula (White, 1845) is crucial to investigate ecological processes. Here we validate a marking method using stable isotope enrichment (15N) of host plants to track spotted lanternfly (SLF), an invasive species causing economic damage on grapes, hardwood forest and landscape tree species. To validate this method, we first determined the isotope dosage to be sprayed on the host plants and subsequently detected in SLF. Second, we examined whether 15N mark remains detectable from the nymphal to adult stage. We demonstrated that two stable isotope dosages applied to the host plants were assimilated by the insect and equally detectable in the exoskeleton, wings, and mature eggs ready to be oviposited. This safe and reliable method can be used to examine fundamental processes of the biology and ecology of SLF that range from dietary resources and resource allocation to food-web structure and dispersal patterns.

Enhanced heat tolerance of viral-infected aphids leads to niche expansion and reduced interspecific competition

Vector-borne pathogens are known to alter the phenotypes of their primary hosts and vectors, with implications for disease transmission as well as ecology. Here we show that a plant virus, barley yellow dwarf virus, increases the surface temperature of infected host plants (by an average of 2 °C), while also significantly enhancing the thermal tolerance of its aphid vector Rhopalosiphum padi (by 8 °C). This enhanced thermal tolerance, which was associated with differential upregulation of three heat-shock protein genes, allowed aphids to occupy higher and warmer regions of infected host plants when displaced from cooler regions by competition with a larger aphid species, R. maidis. Infection thereby led to an expansion of the fundamental niche of the vector. These findings show that virus effects on the thermal biology of hosts and vectors can influence their interactions with one another and with other, non-vector organisms.