Toxic Peptides Occur Frequently in Pergid and Argid Sawfly Larvae

Abstract

Toxic peptides containing D-amino acids are reported from the larvae of sawfly species. The compounds are suspected to constitute environmental contaminants, as they have killed livestock grazing in areas with congregations of such larvae, and related larval extracts are deleterious to ants. Previously, two octapeptides (both called lophyrotomin) and three heptapeptides (pergidin, 4-valinepergidin and dephosphorylated pergidin) were identified from three species in the family Pergidae and one in Argidae. Here, the hypothesis of widespread occurrence of these peptides among sawflies was tested by LC-MS analyses of single larvae from eight pergid and 28 argid species, plus nine outgroup species. At least two of the five peptides were detected in most sawfly species, whereas none in any outgroup taxon. Wherever peptides were detected, they were present in each examined specimen of the respective species. Some species show high peptide concentrations, reaching up to 0.6% fresh weight of 4-valinepergidin (1.75 mg/larva) in the pergid Pterygophorus nr turneri. All analyzed pergids in the subfamily Pterygophorinae contained pergidin and 4-valinepergidin, all argids in Arginae contained pergidin and one of the two lophyrotomins, whereas none of the peptides was detected in any Perginae pergid or Sterictiphorinae argid (except in Schizocerella pilicornis, which contained pergidin). Three of the four sawfly species that were previously known to contain toxins were reanalyzed here, resulting in several, often strong, quantitative and qualitative differences in the chemical profiles. The most probable ecological role of the peptides is defense against natural enemies; the poisoning of livestock is an epiphenomenon.

Endogenous toxins and the coupling of gregariousness to conspicuousness in Argidae and Pergidae sawflies

“…The most striking and regularly encountered defensive strategy among both Argidae and Pergidae larvae is to contain toxic peptides. However, these compounds were neither detected in the sterictiphorines Sterictiphora geminata and Aproceros leucopoda , nor in the pergines Perga affinis and Pergagrapta polita 36 . Pergines use mandibular structures to mechanically sequester toxic leaf compounds as a defense against natural enemies 49 .…”

“…3 ). Among the species used in this test, however, C. janthina contains particularly high amounts of each peptide 36 , and statistical significance was lost when excluding this species from the test (r = 0.174, r 2 = 0.030, P = 0.349; N = 31). Moreover, our stochastic mapping analyses indicated that peptide quantity was not associated with the other traits: diet breadth, gregariousness, predominant body coloration, contrasting spots on body, appearance, and host-plant diversity (Table 1 ).…”

“…Such species actually occur among sawflies. On the one hand, at least five Argidae species are known to contain toxic peptides while being solitary and cryptic 36 (Fig. 2 ).…”

“…To test our hypothesis, we used larvae in the sawfly families Argidae and Pergidae. The larvae of most analyzed species of these closely related groups 34 contain hepta- and octapeptides 35 , 36 . These chemicals are unique among insects and, seemingly even in nature, because of a high proportion of D to L amino acids and due to the presence of phosphoserine 35 .…”

Sawflies (Hymenoptera: Argidae, Pergidae, Tenthredinidae) from southern Ecuador, with a new record for the country and some ecological data

“…It is unclear whether the defence is only physical, or includes chemical compounds. Larvae of Pergidae contain toxic peptides which are active against vertebrates and invertebrates (Boevé et al 2014), but whether Lagideus sp. contains such compounds remains unknown.…”