Distribution of Tomicus destruens (Coleoptera: Scolytinae) mitochondrial lineages: phylogeographic insights and niche modelling

Bioclimatic and Landscape Factors drive the Potential Distribution of Philaenus spumarius, Neophilaenus campestris and N. lineatus (Hemiptera, Aphrophoridae) in Southeastern Iberian Peninsula

Philaenus spumarius and Neophilaenus campestris are the main vectors of the invasive bacteria Xylella fastidiosa and key threats to European plant health. Previous studies of the potential distribution of P. spumarius reveal that climatic factors are the main drivers of its distribution on the Mediterranean Basin scale. Other local studies reveal that the landscape could also have a role in the distribution of both species of P. spumarius and N. campestris. Our work is aimed at understanding the role and importance of bioclimatic and landscape environmental factors in the distributions of the vector and potential vector species P. spumarius, N. campestris, N. lineatus and L. coleoptrata on a regional scale across the Autonomous Community of Murcia (SE Spain), a region with relevant environmental gradients of thermality and crop intensity. We used sweeping nets for sampling 100 points during eight months in 2020. Using bioclimatic landscape composition and topographical variables, we carried out habitat suitability models for each species using the maximum entropy algorithm (MaxEnt). Distribution results for P. spumarius, N. campestris and N. lineatus indicate a gradient in habitat suitability, with the optimum in the coldest and wettest areas in landscapes with a high proportion of forest. All three species are absent from the southern third of the study region, the hottest, driest and most intensively cultivated area. These results are useful and should be considered in contingency plans against possible invasions of X. fastidiosa in Mediterranean regions.

Application of propylene glycol in DNA-based studies of invertebrates

High-throughput sequencing (HTS) studies on invertebrates commonly use ethanol as the main sample fixative (upon collection) and preservative (for storage and curation). However, alternative agents exists, which should not be automatically neglected when studies are newly designed. This review provides an overview of the application of propylene glycol (PG) in DNA-based studies of invertebrates, thus to stimulate an evidence-based discussion.

The use of PG in DNA-based studies of invertebrates is still limited (n = 79), but a steady increase has been visible since 2011. Most studies used PG as a fixative for passive trapping (73%) and performed Sanger sequencing (66%; e.g. DNA barcoding). More recently, HTS setups joined the field (11%). Terrestrial Coleoptera (30%) and Diptera (20%) were the most studied groups. Very often, information on the grade of PG used (75%) or storage conditions (duration, temperature) were lacking. This rendered direct comparisons of study results difficult, and highlight the need for further systematic studies on these subjects.

When compared to absolute ethanol, PG can be more widely and cheaply acquired (e.g. as an antifreeze, 13% of studies). It also enables longer trapping intervals, being especially relevant at remote or hard-to-reach places. Shipping of PG-conserved samples is regarded as risk-free and is authorised, pinpointing its potential for larger trapping programs or citizen science projects. Its property to retain flexibility of morphological characters as well as to lead to a reduced shrinkage effect was especially appraised by integrative study designs. Finally, the so far limited application of PG in the context of HTS showed promising results for short read amplicon sequencing and reduced representation methods. Knowledge of the influence of PG fixation and storage for long(er) read HTS setups is currently unavailable.

Given our review results and taking difficulties of direct methodological comparisons into account, future DNA-based studies of invertebrates should on a case-by-case basis critically scrutinise if the application of PG in their anticipated study design can be of benefit.

Climatic niche comparison between closely related trans-Palearctic species of the genus Orthocephalus (Insecta: Heteroptera: Miridae: Orthotylinae)

Previously climatic niche modelling had been studied for only a few trans-Palearctic species. It is unclear whether and to what extent those niches are different, and which climatic variables influence such a wide distribution. Here, environmental niche modelling is performed based on the Worldclim variables using Maxent for eight species of the genus Orthocephalus (Insecta: Heteroptera: Miridae: Orthotylinae). This group belongs to one of the largest insect families and it is distributed across Palearctic. Orthocephalus bivittatus, O. brevis, O. saltator and O. vittipennis are distributed across Europe and Asia; O. coriaceus, O. fulvipes, O. funestus, O. proserpinae have more limited distribution. Niche comparison using ENMTools was also undertaken to compare the niches of these species, and to test whether the niches of closely related species with trans-Palearctic distributions are more similar to each other, than to other congeners. It has been found that climatic niche models of all trans-Palearctic species under study are similar but are not identical to each other. This has been supported by niche geographic projections, climatic variables contributing to the models and variable ranges. Climatic niche models of all the trans-Palearctic Orthocephalus species are also very similar to two species having more restricted distribution (O. coriaceus, O. funestus). Results of this study suggest that trans-Palearctic distributions can have different geographic ranges and be shaped by different climatic factors.