Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Susceptibility of leatherjackets (Tipula paludosa and Tipula oleracea; Tipulidae; Nematocera) to the entomopathogenic nematode Steinernema feltiae.

Abstract

Laboratory bioassays were conducted to investigate the susceptibility of larvae of Tipula paludosa and T. oleracea to Steinernema feltiae [Steinernema bibionis]. Dauer juveniles (DJs) entered the larval haemocoel mainly by direct penetration of the cuticle and were encapsulated in the haemocoel in all except 1st instars. Depending on the number of invading nematodes larval death could be prevented by this encapsulation. Larval mortality was correlated with the number of invading nematodes, indicating that penetration by DJs was the limiting step during pathogenesis. In contrast to other instars, the dose-mortality response of young 1st instars was less pronounced. T. oleracea was more susceptible to S. bibionis than T. paludosa. In both Tipula species maximum mortality was recorded for the 1st instar approaching the 1st moult, while young 1st instars were less susceptible. Susceptibility of 2nd- to 4th-instar larvae decreased with their age. For T. oleracea, LC50 values ranged from 7 DJs per insect for the 1st instar approaching the 1st moult, to 56 DJs for the 4th instar. Nematode invasion was not correlated to CO2 release by the different larval stages. It was therefore, concluded that penetration was not triggered by CO2, but by other more specific stimuli.