Effects of group size and pine defence chemicals on Diprionid sawfly survival against ant predation

Abstract

The defence chemicals and behavioural adaptations (gregariousness and active defensive behaviour) of pine sawfly larvae may be effective against ant predation. However, previous studies have tested their defences against very few species of ants, and few experiments have explored ant predation in nature. We studied how larval group size (groups of 5 and 20 in Neodiprion sertifer and 10, 20 and 40 in Diprion pini) and variation in levels of defence chemicals in the host tree (Scots pine, Pinus sylvestris) affect the survival of sawfly larvae. Food preference experiments showed that ants do eat sawfly larvae, although they are not their most preferred food item. According to our results, ant predation significantly increases the mortality rate of sawfly larvae. Larval mortality was minor on pine tree branches where ant traffic was excluded. We also found that a high resin acid concentration in the host tree significantly decreased the mortality of D. pini larvae when ants were present. However, there was no such relationship between the chemical concentrations of the host tree and larval mortality for N. sertifer. Surprisingly, grouping did not help sawfly larvae against ant predation. Mortality risk was the same for all group sizes. The results of the study seemingly contradict previous understanding of the effectiveness of defence mechanisms of pine sawfly against ant predation, and suggest that ants (Formica exsecta in particular) are effective predators of sawfly larvae.

Histology of the LarvalNeodiprion abietis(Hymenoptera: Diprionidae) Digestive Tract

“…Sawflies are phytophagous and the Diprionidae are defoliators of conifer trees (Pinaceae) with digestive systems adapted to that purpose. The diverticular pouches, which branch off the diprionid larval foregut, are used to store hostplant-derived terpenoids that are regurgitated in defensive behaviors against predators [21][22][23][24][25][26][27]. Like N. abietis, the diverticular pouches of N. sertifer larvae have been shown to be muscular sacs lined with an impervious layer of cuticle [21].…”

Larval Aggregation of Heortia vitessoides Moore (Lepidoptera: Crambidae) and Evidence of Horizontal Transfer of Avermectin

“…Social aggregation is one of the strategies that provide protective and facilitation effects aiding the survival and development of larvae [25], and has arisen independently in diverse animal taxa [26][27][28][29][30]. The majority of insects have immature stages, and the aggregation behaviors of larvae have been reported in many lineages including true flies [24,[31][32][33], sawflies [34][35][36][37], and beetles [38][39][40].…”

Can the absence of ants interfere in the arthropods abundance on corn plants (Zea mays L. - Poaceae)?

“…According to the results of this Other study showed that Dermaptera of genus Dorus are efficient herbivorous predators in corn monoculture (see Cruz 1991). Additionally, Buschman et al (1977) Some studies have shown that the result of ant-plant interaction is dependent of the species of predatory ants involved interaction (Byk & Del-Claro, 2010;Calabuig et al, 2015) and of the strategies of herbivorous against predation (Bächtold & Alves-Silva, 2013;Carita et al, 2006;Styrsky & Eubanks, 2010). Nevertheless, little is known about the behavior between pairs (predator-prey) determining plant protection.…”