Nutrient Utilization during Male Maturation and Protein Digestion in the Oriental Hornet

Males of social Hymenoptera spend the first days following eclosion inside the nest before dispersing to find a young queen to mate with. During this period, they must acquire enough nutrients to enable their sexual maturation and store energy to sustain them through their nuptial journey. It was previously argued that adult hornets are unable to process dietary proteins and rely on the larvae to supply them with free amino acids and carbohydrates that they secrete via trophallaxis. Using isotopically enriched diets, we examined nutrient allocation and protein turnover in newly-emerged males of the Oriental hornet during their maturation period and tested the protein digestion capability in the presence and absence of larvae in both males and worker hornets. The results indicated that protein turnover in males occurs during the first days following eclosion, while carbohydrates are incorporated into body tissues at higher rates towards the end of the maturation period. Additionally, we found that males cannot digest protein and depend on larval secretions as a source of nutrition, while workers, in contrast to previous reports, can metabolize protein independently. Our findings demonstrate the contribution of adult male nutrition and larval secretions to colony fitness

Morphological and Molecular Revision of the Genus Ozirhincus (Diptera: Cecidomyiidae)—Long-Snouted Seed-Feeding Gall Midges on Asteraceae

The Palaearctic gall-midge genus Ozirhincus is unique among the Cecidomyiidae for its morphology and biology. Unlike most other phytophagous gall midges, species in this genus do not induce galls but develop inside achenes of Asteraceae plants. The heads of adults are characterized by an unusually elongate proboscis, the function of which is unclear. Despite a lot of attention from taxonomists in the 19th and early 20th century, a proper revision of the genus has been hindered by complex host associations, the loss of most relevant type material, and the lack of a thorough comparative study of all life stages. The present revision integrated morphological, molecular, and life-history data to clearly define species boundaries within Ozirhincus, and delimit host-plant ranges for each of them. A phylogenetic analysis based on the mitochondrial COI and 16S genes confirmed the validity of four distinct species but did not resolve the relationships among them. All species are oligophages, and some may occur together on the same host plant. Species with wider host-plant ranges have wider European and circum-Mediterranean distribution ranges, whereas species with narrower host ranges are limited to Europe and the Russian Far East. As part of the present work, O. hungaricus is reinstated from synonymy, O. tanaceti is synonymized under O. longicollis, neotypes are designated for O. longicollis and O. millefolii, and a lectotype is designated for O. anthemidis

Nutrient Utilization during Male Maturation and Protein Digestion in the Oriental Hornet

Males of social Hymenoptera spend the first days following eclosion inside the nest before dispersing to find a young queen to mate with. During this period, they must acquire enough nutrients to enable their sexual maturation and store energy to sustain them through their nuptial journey. It was previously argued that adult hornets are unable to process dietary proteins and rely on the larvae to supply them with free amino acids and carbohydrates that they secrete via trophallaxis. Using isotopically enriched diets, we examined nutrient allocation and protein turnover in newly-emerged males of the Oriental hornet during their maturation period and tested the protein digestion capability in the presence and absence of larvae in both males and worker hornets. The results indicated that protein turnover in males occurs during the first days following eclosion, while carbohydrates are incorporated into body tissues at higher rates towards the end of the maturation period. Additionally, we found that males cannot digest protein and depend on larval secretions as a source of nutrition, while workers, in contrast to previous reports, can metabolize protein independently. Our findings demonstrate the contribution of adult male nutrition and larval secretions to colony fitness

Pupae heads.

<p>a. <i>Ozirhincus anthemidis</i>, frontal; b. <i>O</i>. <i>anthemidis</i>, lateral; c. <i>O</i>. <i>hungaricus</i>, frontal; c. <i>O</i>. <i>hungaricus</i>, lateral; e. <i>O</i>. <i>longicollis</i>, frontal; f. <i>O</i>. <i>millefolii</i>, frontal.</p

Male abdomen, <i>Ozirhincus anthemidis</i>.

<p>a. Post abdomen and terminalia, lateral; b. Terminalia, dorsal, setation shown on right gonopod; c. Terminalia, lateral, one gonopod removed; d. Terminalia, ventral, showing mediobasal lobes and aedeagus; e. Gonostylus, dorsal (top), ventral (bottom). Aed–Aedeagus, Cer–cercus, Dl–Dorsal part of mediobasal lobe, Gs–Gonostylus, Gx–Gonocoxite, Vl–Ventral part of mediobasal lobe. Scale bars = 0.1 mm.</p

Phylogenetic tree of <i>Ozirhincus</i> Rondani based on Bayesian analysis of partial sequence of the cytochrome oxidase subunit I (COI) and ribosomal RNA16S mitochondrial genes.

<p>Support values are shown next to nodes, above branches. Character states representing proboscis length as suggested by the ancestral states analysis are shown below branches (in square brackets). Letters and numbers following species name refer to collecting localities and dates (details in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130981#pone.0130981.t002" target="_blank">Table 2</a>). Colors correspond to host-plant genera.</p

<i>Ozirhincus hungaricus</i>.

<p>a-c. Female on <i>Tanacetum vulgare</i> inflorescence (photos: Hedy Jansen); d. <i>Tanacetum vulgare</i> flowers containing <i>O</i>. <i>hungaricus</i> larvae (upper row), and normal flowers (lower row).</p

Adult heads.

<p>a. <i>Ozirhincus anthemidis</i>, male; b. <i>O</i>. <i>hungaricus</i>, male; c. <i>O</i>. <i>millefolii</i>, female; d. <i>O</i>. <i>longicollis</i>, female; e. <i>O</i>. <i>longicollis</i>, male, showing typical shape of flagellomeres.</p

Larvae.

<p>a. <i>O</i>. <i>anthemidis</i>, head; b. <i>O</i>. <i>anthemidis</i>, spatula and associated papillae; c. <i>O</i>. <i>anthemidis</i>, terminal abdominal segment; d. <i>O</i>. <i>hungaricus</i>, terminal abdominal segment. e. Spatula and associated papillae, <i>O</i>. <i>hungaricus</i>; f. Spatula and associated papillae, <i>O</i>. <i>longicollis</i>; g. Spatula and associated papillae, <i>O</i>. <i>millefolii</i>; h. Variation of spatula shape in <i>O</i>. <i>anthemidis</i>; i. Variation of spatula shape in <i>O</i>. <i>hungaricus</i>. Lp–Lateral papillae, Sp–Sternal papilla, Vp–Ventral papilla. Scale bars = 0.1 mm.</p

Potential Asteraceae host plants screened in this study for the presence of <i>Ozirhincus</i> gall midges.

<p>Potential Asteraceae host plants screened in this study for the presence of <i>Ozirhincus</i> gall midges.</p