Lateral Transmission of Yeast Symbionts Among Lucanid Beetle Taxa.

To deepen understanding the evolutionary process of lucanid-yeast association, the lateral transmission process of yeast symbionts among stag beetle genera Platycerus and Prismognathus around the border between Japan and South Korea was estimated based on molecular analyses and species distribution modelings. Phylogenetic analyses were based on yeast ITS and IGS sequences and beetle COI sequences using Prismognathus dauricus from the Tsushima Islands and Pr. angularis from Kyushu, Japan, as well as other sequence data from our previous studies. The range overlap based on the species distribution model (SDM) and differentiation in ecological space were analyzed. Based on the IGS sequences, Clade II yeast symbionts were shared by Platycerus hongwonpyoi and Pr. dauricus in South Korea and the Tsushima Islands, and Platycerus viridicuprus in Japan. Clade III yeasts were shared by Pr. dauricus from the Tsushima Islands and Pr. angularis in Japan. During the Last Interglacial period when the land bridge between Japan and the Korean Peninsula existed, range overlap was predicted to occur between Pl. viridicuprus and Pr. dauricus in Kyushu and between Pr. dauricus and Pr. angularis in Kyushu and the Tsushima Islands. The ecological space of Pl. hongwonpyoi was differentiated from that of Pl. viridicuprus and Pr. angularis. We demonstrated the paleogeographical lateral transmission process of Scheffersomyces yeast symbionts among lucanid genera and species: putative transmission of yeasts from Pr. dauricus to Pl. viridicuprus in Kyushu and from Pr. angularis to Pr. dauricus in Kyushu or the Tsushima Islands. We also found that the yeast symbionts are likely being replaced in Pr. dauricus on the Tsushima Islands. We present novel estimates of the lateral transmission process of microbial symbionts based on phylogenetic, SDM and environmental analyses among lucanid beetles.

Diverse Heat Tolerance of the Yeast Symbionts of Platycerus Stag Beetles in Japan.

The genus Platycerus (Coleoptera: Lucanidae) is a small stag beetle group, which is adapted to cool-temperate deciduous broad-leaved forests in East Asia. Ten Platycerus species in Japan form a monophyletic clade endemic to Japan and inhabit species-specific climatic zones. They are reported to have co-evolutionary associations with their yeast symbionts of the genus Sheffersomyces based on host cytochrome oxidase subunit I (COI) and yeast intergenic spacer (IGS) phylogenies. Here we examined the heat tolerances of the yeast colonies isolated from the mycangia of 37 females belonging ten Japanese Platycerus species. The upper limits of growth and survival temperatures of each colony were decided by cultivating it at ten temperature levels between 17.5 and 40°C. Although both temperatures varied during 25.0-31.25°C, the maximum survival temperatures (MSTs) were a little higher than the maximum growth temperatures (MGTs) in 16 colonies. Pearson's correlations between these temperatures and environmental factors (elevation and 19 bioclimatic variables from Worldclim database) of host beetle collection sites were calculated. These temperatures were significantly correlated with elevation negatively, the maximum temperature of the warmest month (Bio5) positively, and some precipitative variables, especially in the warm season (Bio12, 13, 16, 18) negatively. Sympatric Platycerus kawadai and Platycerus albisomni share the same lineage of yeast symbionts that exhibit the same heat tolerance, but the elevational lower range limit of P. kawadai is higher than that of P. albisomni. Based on the field survey in their sympatric site, the maximum temperature of host wood of P. kawadai larvae is higher about 2-3°C than that of P. albisomni larvae in the summer, which may restrict the elevational range of P. kawadai to higher area. In conclusion, it is suggested that the heat tolerance of yeast symbionts restricts the habitat range of their host Platycerus species or/and that the environmental condition that host Platycerus species prefers affect the heat tolerance of its yeast symbionts.

Red imported fire ants (Hymenoptera: Formicidae) cover inaccessible surfaces with particles to facilitate food search and transportation.

Eusocial insects have evolved diverse particle-use behaviors. A previous study reported that red imported fire ants, Solenopsis invicta Buren, deposited soil particles on substances treated with essential balm, a fire ant repellent. We hypothesized that S. invicta modifies inaccessible surfaces by covering them with soil particles to facilitate food search and transportation. Here, laboratory experiments were conducted to study the particle-covering behavior of S. invicta in response to viscose surfaces or surfaces treated with essential balm or liquid paraffin in the presence of real food (sausage) or non-food objects (acrylic plates). S. invicta workers deposited significantly more soil particles on these three types of treated surfaces than on untreated surfaces. In addition, significantly more particles were relocated on viscose and paraffin-smeared surfaces in the presence of food than in the presence of non-food objects. The particle-covering behavior on viscose surfaces was also observed in the field. Interestingly, when no soil particles were available, ants searched and transported food on viscose surfaces only if the surfaces were artificially covered with sufficient quantities of soil particles but could not do so on viscose surfaces without soil particles or with insufficient quantities of soil particles. In addition, ants actively relocated particles to cover viscose surfaces if the transportation distance was within 200 mm, whereas significantly fewer particles were relocated at longer transportation distances (400 mm). Our study provides a novel example of particle use by fire ants during foraging.

How do groups of red imported fire ants (Hymenoptera: Formicidae) feed on a droplet of sugar water?

Many previous studies have focused on the foraging behaviors and strategies of the red imported fire ants, Solenopsis invicta Buren on solid food or granular bait; little attention has been paid to how liquid sugar is fed upon. In the present study, behavioral responses of S. invicta to 25% sucrose water droplets were observed. Five foraging patterns were identified in S. invicta colonies under laboratory conditions: (i) no feeding, no sucrose water feeding was observed; (ii) surround feeding, ants surrounded and fed along the edge of the sucrose droplet; (iii) stacked feeding, ants stacked and fed along the edge of the sucrose droplet; (iv) droplet-break feeding, ants broke the liquid droplet and sucked sucrose water that spread on surface of the substance or soil particles previously transported by ants; and (v) cover feeding, whole surface of the sucrose droplet was covered by layers of feeding ants. This is the first time cover feeding in S. invicta has been reported, which obviously requires more ants compared to the other patterns. In addition, individual ants were tracked in videos under laboratory conditions, and behavioral repertoires that led to stacking, covering and droplet-breaking were identified and described. The field investigation showed that surround feeding was most frequently performed by S. invicta foragers; however, cover feeding was not observed under field conditions during this study. Both laboratory and field studies showed colony-level variations in sugar-water feeding.

Analysis of Tea Geometrid (Ectropis grisescens) Pheromone Gland Extracts Using GC-EAD and GC×GC/TOFMS.

The tea geometrid, Ectropis grisescens Warren, is one of the most severe defoliator insect pests in tea plantations, China. The use of insecticides, etc., is forbidden on organic tea plantations. No female-produced sex pheromones of E. grisescens had been previously identified. In the present study, female gland extracts were analyzed by gas chromatography coupled with electroantennographic detection (GC-EAD) and two-dimensional gas chromatography (GC×GC) using a time-of-flight mass spectrometric detector (TOFMS). Two components, (Z,Z,Z)-3,6,9-octadecatriene (Z3Z6Z9-18:Hy) and (Z,Z)-3,9-6,7-epoxyoctadecadiene (Z3Z9-6,7-epo-18:Hy), were identified from pheromone gland extracts, and their electrophysiological and behavioral activity evaluated. Under laboratory conditions, Z3Z9-6,7-epo-18:Hy elicited a stronger electrophysiological response than Z3Z6Z9-18:Hy. In the field, traps baited with Z3Z9-6,7-epo-18:Hy alone showed better results than traps baited with Z3Z6Z9-18:Hy, and the binary mixture of Z3Z9-6,7-epo-18:Hy and Z3Z6Z9-18:Hy in a ratio of 4:1 (approximate ratio of females emitting pheromone) caught more males than the single components or any other blends. This study showed that Z3Z6Z9-18:Hy and Z3Z9-6,7-epo-18:Hy are the sex pheromone components of E. grisescens and that they prove useful in developing alternative management tools for the pest.

Electrophysiological and behavioral responses of Diaphania glauculalis males to female sex pheromone.

The aim of this study is to identify the pheromone active component of female moths, Diaphania glauculalis, an important pest of Anthocephalus chinensis in China. The sex pheromone was extracted from sex pheromone gland extracts of virgin female moth of D. glauculalis using n-hexane, and the pheromone gland extracts of females were analyzed using coupled gas chromatography-electroantennogram detection (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). The sex pheromone active components were based on the comparison the retention time and mass spectrum, with suitable synthetic compounds. (E)-11-hexadecenal (E11-16:Ald) and (E,E)-10,12-hexadecadienal (E10E12-16:Ald) were identified as the major sex pheromone components in the females. Their biological activities were evaluated in a series of electroantennogram (EAG) experiments and four-arm olfactometer assays using synthetic compounds. D. glauculalis males could be attracted by any single component, but a mixture of the E11-16:Ald and E10E12-16:Ald in a ratio of 5:5 elicited a substantial response, demonstrating that the binary blend is essential in male attraction. We therefore conclude that the aldehyde compounds, a mixture of E11-16:Ald and E10E12-16:Ald, comprise the sex pheromone components of D. glauculalis, which might be applied for insect field trapping.