ABSTRACT
Proto-anhydrobiosis of the nematode, Beddingia siricidicola, was achieved by incubation in polyethylene glycol or various concentrations up to 4 M of glycerol. The associated changes in the levels of glycerol, unbound proline, trehalose, lipids, and glycogen were determined by alkylation strategies, followed by gas chromatography or gas chromatography/mass spectrometry. The level of glycerol reached 8.9% of dry weight, proline 2.4% of dry weight, and trehalose 8.0% of dry weight within B. siricidicola that were incubated in 1.5 M glycerol over 6 d, while glycerol reached 17.9% of dry weight after incubation for the same period in 4 M glycerol. Movement was thereby reduced but the nematodes from 1.5 M glycerol revived after a few minutes upon rehydrating and they were able to avoid osmotic damage by rapidly excreting the glycerol, much of it being expelled within the first hour. The potential for storage and transport of this nematode for the biological control of the pine-killing wasp, Sirex noctilio, was greatly improved when nematode suspensions were maintained in 1.5 M glycerol under refrigeration.
ABSTRACT
The corticoid fungus, Amylostereum areolatum, is deposited in pine trees by the woodwasp, Sirex noctilio, at the time of oviposition. This fungus is essential in S. noctilio larval growth and it is also a food source for Beddingia siricidicola, the nematode used for S. noctilio biological control. In recent years, the historically successful biological control programme has been disrupted in Australia by the bark beetle, Ips grandicollis. This study investigated whether the mechanism of this disruption involves a fungus, Ophiostoma ips, which I. grandicollis introduces into trees. In artificial and wood media, A. areolatum was unable to grow in areas occupied by O. ips. The latter fungus was faster growing, especially at 25 °C rather than 20 °C. Larval galleries of S. noctilio in field-collected samples were strongly associated with wood infested by A. areolatum and absent from areas affected by O. ips. The nematode failed to survive and reproduce on O. ips as it can on A. areolatum. Competitive interactions between O. ips and A. areolatum within the trap trees are demonstrated to be key factors in the negative effect of I. grandicollis on S. noctilio biological control programmes.
Subject(s)
Biological Control Agents , Coleoptera , Nematoda , Pinus , Wasps , Animals , Australia , Basidiomycota/growth & development , Competitive Behavior , Female , Trees , Wasps/microbiology , WoodABSTRACT
Two hypotheses on the synthesis of the protectants glycerol and trehalose of the infective juveniles (IJs) of Steinernema carpocapsae during osmotic dehydration were tested and utilised to evaluate the function and importance of glycerol on survival of the nematodes during osmotic dehydration. This was achieved by comparing the changes in survival, morphology, behaviour and levels of glycerol, trehalose and permeated compounds of the IJs dehydrated in seven hypertonic solutions at two temperature regimes: (1) 5 degrees C for 15 days; and (2) 23 degrees C for 1 day followed by 5 degrees C for another 14 days. The results substantiate both hypotheses tested: (1) the permeability of the IJs to various compounds, such as sucrose or ethylene glycol, when they are dehydrated in hypertonic solutions of these compounds; and (2) suppression of the synthesis of protectant glycerol but not trehalose when IJs are dehydrated at low temperature. The results also showed that: (1) although trehalose was the preferred dehydration protectant, glycerol played an important role in rapidly balancing the osmotic pressure when IJs were exposed in hypertonic solutions; (2) the presence of glycerol was essential for the IJs to survive and function properly even under moderate osmotic dehydration, especially when IJs were dehydrated in salt solutions; and (3) some exogenous compounds permeated into IJs during osmotic dehydration such as ethylene glycol, may function in the same way as glycerol and significantly improve the survival and function of the IJs. The results indicate that each of the protectants glycerol and trehalose has a specific function and neither is replaceable by the other.
