Fossils in Myanmar amber demonstrate the diversity of anti-predator strategies of Cretaceous holometabolan insect larvae.

Holometabolan larvae are a major part of the animal biomass and an important food source for many animals. Many larvae evolved anti-predator strategies and some of these can even be recognized in fossils. A Lagerstätte known for well-preserved holometabolan larvae is the approximately 100-million-year-old Kachin amber from Myanmar. Fossils can not only allow to identify structural defensive specializations, but also lifestyle and even behavioral aspects. We review here the different defensive strategies employed by various holometabolan larvae found in Kachin amber, also reporting new cases of a leaf-mining hymenopteran caterpillar and a hangingfly caterpillar with extensive spines. This overview demonstrates that already 100 million years ago many modern strategies had already evolved in multiple lineages, but also reveals some cases of now extinct strategies. The repetitive independent evolution of similar strategies in distantly related lineages indicates that several strategies evolved convergently as a result of similar selective pressures.

Morphology of the abdominal segmental glands and spinning behaviour of Stenus larvae (Coleoptera, Staphylinidae).

We focus on the morphology of the "segmental glands" and their openings in third instar Stenus larvae. The location of the openings was similar in both studied species, with paired rosette-like structures present on the head, all thoracic segments and abdominal segments 1-9. No such openings could be found on the antennae, the maxillary palps, the urogomphi, and the legs as suggested in some older publications. We presume that the glands up to abdominal segment 7 are "adhesive" glands. They are compound glandular units consisting of a secretory syncytium with a common reservoir and a canal cell. The common reservoir is connected through a single efferent duct with the opening of the gland. Glands of abdominal segments 8 and 9 show differences in their length, number of reservoirs, the orientation of the efferent canal, the inner structures of the gland openings towards the exterior and the shape and content of the secretion vesicles indicating that they are silk glands for cocoon building. The spinning behaviour has been observed during the building of the hatching and pupation retreats. The larva first attaches to the substrate with its pygopod, secretes silk droplets from silk gland openings and pulls out a silk filament from the tip of its urogomphi. Whereas L1 and L2 instars produce an open single-layered net, L3 build a closed bi-layered cocoon.

The Morphological Diversity of Antlion Larvae and Their Closest Relatives over 100 Million Years.

Among lacewings (Neuroptera), representatives of the groups Ascalaphidae (owlflies) and Myrmeleontidae (antlions) are likely the most widely known ones. The exact taxonomic status of the two groups remains currently unclear, each may in fact be nested in the other group. Herein, we refer to the group including representatives of both with the neutral term "owllion". Owllion larvae are voracious ambush hunters. They are not only known in the extant fauna, but also from the fossil record. We report here new findings of a fossil owlfly larva from Eocene Baltic amber, as well as several owlfly-like larvae from Cretaceous Kachin amber, Myanmar. Based on these fossils, combined with numerous fossil and extant specimens from the literature, collections, and databases, we compared the morphological diversity of the head and mouthpart shapes of the larvae of owllions in the extant fauna with that of owllion-like larvae from three time slices: about 100 million years ago (Cretaceous), about 40 million years ago (Eocene), and about 20 million years ago (Miocene). The comparison reveals that the samples from the Eocene and Miocene are too small for a reliable evaluation. Yet, the Cretaceous larvae allow for some conclusions: (1) the larval morphological diversity of owllion larvae increased over time, indicating a post-Cretaceous diversification; (2) certain morphologies disappeared after the Cretaceous, most likely representing ecological roles that are no longer present nowadays. In comparison, other closely related lineages, e.g., silky lacewings or split-footed lacewings, underwent more drastic losses after the Cretaceous and no subsequent diversifications.

The first fossil immature of Elmidae: an unusual riffle beetle larva preserved in Baltic amber.

Elmidae, riffle beetles, have both adult and immature stages that show specializations for water environments. Fossils of adults of Elmidae are already known from amber, however a record of immatures was so far lacking. We report here the first fossil larva of Elmidae, preserved in Baltic amber. To be able to access details of the body hidden by inclusions and "Verlumung" we conducted, in addition to optical documentation methods, micro-CT and synchrotron documentation methods. The larva is characterised by prominent dorso-lateral and lateral processes and a plate-like ventral operculum at the end of the abdomen. The new fossil has similarities in the general body shape and the prominent characters with some modern larvae of Elmidae. The posterior protrusions on the trunk end possibly represent gills, which would imply that fossil larvae of Elmidae also led a water-related life style similar to modern representatives.

Changes in the Morphological Diversity of Larvae of Lance Lacewings, Mantis Lacewings and Their Closer Relatives over 100 Million Years.

Neuroptera, the group of lacewings, comprises only about 6000 species in the modern fauna, but is generally assumed to have been more diverse and important in the past. A major factor of the modern-day ecological diversity of the group, and supposedly in the past as well, is represented by the highly specialised larval forms of lacewings. Quantitative analyses of the morphology of larvae revealed a loss of morphological diversity in several lineages. Here we explored the diversity of the larvae of mantis lacewings (Mantispidae), lance lacewings (Osmylidae), beaded lacewings (Berothidae and Rhachiberothidae, the latter potentially an ingroup of Berothidae), and pleasing lacewings (Dilaridae), as well as fossil larvae, preserved in amber, resembling these. We used shape analysis of the head capsule and stylets (pair of conjoined jaws) as a basis due to the high availability of this body region in extant and fossil specimens and the ecological importance of this region. The analysis revealed a rather constant morphological diversity in Berothidae. Mantispidae appears to have lost certain forms of larvae, but has seen a drastic increase of larval diversity after the Cretaceous; this is in contrast to a significant decrease in diversity in adult forms.