Body distribution of toxic peptides in larvae of a pergid and an argid sawfly species

Behavior and body size modulate the defense of toxin-containing sawfly larvae against ants

The sawfly larvae of most Argidae and Pergidae (Hymenoptera: Symphyta) species contain toxic peptides, and these along with other traits contribute to their defense. However, the effectiveness of their defense strategy, especially against ants, remains poorly quantified. Here, five Arge species, A. berberidis, A. nigripes, A. ochropus, A. pagana, A. pullata, plus three Pergidae species, Lophyrotoma analis, Lophyrotoma zonalis, Philomastix macleaii, were tested in laboratory bioassays on ant workers mainly of Myrmica rubra. The experiments focused on short-term predator-prey interactions, sawfly survival rate after long-term interactions, and feeding deterrence of the sawfly hemolymph. The larvae of Arge species were generally surrounded by few ants, which rarely bit them, whereas larvae of Pergidae, especially P. macleaii, had more ants around with more biting. A detailed behavioral analysis of Arge-ant interactions revealed that larval body size and abdomen raising behavior were two determinants of ant responses. Another determinant may be the emission of a volatile secretion by non-eversible ventro-abdominal glands. The crude hemolymph of all tested species, the five Arge species and L. zonalis, was a strong feeding deterrent and remained active at a ten-fold dilution. Furthermore, the study revealed that the taxon-specific behavior of ants, sting or spray, impacted the survival of A. pagana but not the large body-sized A. pullata. The overall results suggest that the ability of Arge and Pergidae larvae to defend against ants is influenced by the body size and behavior of the larvae, as well as by chemicals.

Some sawfly larvae survive predator-prey interactions with pentatomid Picromerus bidens

Most Asopinae stinkbugs (Hemiptera: Pentatomidae) prey on other insects, including sawfly larvae (Hymenoptera: Symphyta). Sawfly larvae of the Argidae and Pergidae contain toxic peptides, but whether they are defended against stinkbugs remains poorly studied. A literature survey indicates that no publication is devoted to laboratory tests specifically using these sawflies against stinkbugs. Here, laboratory bioassays were made with the stinkbug Picromerus bidens and four sawfly species at last larval instars: Arge ochropus (Argidae), Arge pagana (also tested at medium instars), Lophyrotoma zonalis (Pergidae), and Allantus rufocinctus (Tenthredinidae). Following 24 h of possible predator-prey interactions, no larvae of A. rufocinctus survived, whereas most or all larvae of the other sawfly species did survive and were still alive 48 h later. When feeding on an argid or pergid larva, the feeding periods lasted on average 6-20 s only, some bugs removing their rostrum and abruptly backing away. Full-grown larvae of A. pagana were attacked less than younger ones. It is likely that the tested Argidae and Pergidae are well defended against P. bidens by potent, internal antifeedants, while defensive body movements combined with a large body size play a secondary role.

Craniofacial ontogeny in Tylosaurinae

Mosasaurs were large, globally distributed aquatic lizards that lived during the Late Cretaceous. Despite numerous specimens of varying maturity, a detailed growth series has not been proposed for any mosasaur taxon. Two taxa-Tylosaurus proriger and T. kansasensis/nepaeolicus-have robust fossil records with specimens spanning a wide range of sizes and are thus ideal for studying mosasaur ontogeny. Tylosaurus is a genus of particularly large mosasaurs with long, edentulous anterior extensions of the premaxilla and dentary that lived in Europe and North America during the Late Cretaceous. An analysis of growth in Tylosaurus provides an opportunity to test hypotheses of the synonymy of T. kansasensis with T. nepaeolicus, sexual dimorphism, anagenesis, and heterochrony. Fifty-nine hypothetical growth characters were identified, including size-dependent, size-independent, and phylogenetic characters, and quantitative cladistic analysis was used to recover growth series for the two taxa. The results supported the synonymy of T. kansasensis with T. nepaeolicus and that T. kansasensis represent juveniles of T. nepaeolicus. A Spearman rank-order correlation test resulted in a significant correlation between two measures of size (total skull length and quadrate height) and maturity. Eleven growth changes were shared across both species, neither of the ontogram topologies showed evidence of skeletal sexual dimorphism, and a previous hypothesis of paedomorphy in T. proriger was not rejected. Finally, a novel hypothesis of anagenesis in Western Interior Seaway Tylosaurus species, driven by peramorphy, is proposed here.