Robin Anthony Bedding

Controlling the Pine-Killing Woodwasp, Sirex noctilio, with Nematodes

The pine-killing woodwasp Sirex noctilio, a native to Eurasia/Morocco, was accidentally introduced into various Southern Hemisphere countries during the last century and has recently (2005) been detected in north-eastern North America. The parasitic nematode Beddingia siricidicola is by far the most important control agent of sirex and has been introduced into each Southern Hemisphere country soon after sirex became established. The nematode has a complex life cycle with morphologically very different forms. One form feeds on the tree-pathogenic, sirex-symbiotic fungus (Amylostereum areolatum) as this fungus grows throughout the tree, while the other form grows in and then sterilises adult female S. noctilio. The fungal-feeding form of B. siricidicola is used to mass-produce the nematode. Methods are described for liberating nematodes in pine plantations. The nematode has caused major crashes in S. noctilio populations so that sirex-infested trees can no longer be found in many plantations. A problem arose when it was discovered that long-term in vitro culture using only the fungal cycle without intervention of parasitic cycles had selected, over many years, for a nematode strain (the “defective strain”) that rarely formed the infective stage and was therefore much less effective in the field. Isolation of the “Kamona strain”, annual replenishment from liquid nitrogen storage and other procedural changes are enabling strain replacement in the field. While nematode control in most of the Southern Hemisphere has proved to be highly successful, there are problems in the KwaZulu-Natal region of South Africa where warm dry winters cause sirex-infested trees to dry out before the nematode populations can spread throughout the tree. In North America an inferior strain of nematode appears to have been accidentally introduced with sirex. The symbiotic fungus of sirex introduced to North America is a different strain of A. amylostereum to that in the Southern Hemisphere and does not permit optimal nematode development.

Energy metabolism and its relation to survival and infectivity of infective juveniles of Steinernema carpocapsae under aerobic conditions

Energy metabolism of the infective juveniles (IJ) of Steinernema carpocapsae under aerobic conditions and its relation to survival and infectivity of the IJ was studied by monitoring the changes in mean dry weight, levels of key energy reserve compounds, oxygen consumption rate, respiratory quotient, survival and infectivity of freshly harvested IJ incubated in tap water on a shaker at 28°C over time. The survival rate of the IJ exceeded 90% for the first 6 weeks and then dropped sharply to about 50% at week 8. The infectivity of the IJ did not change markedly within the first 3 weeks, dropped slightly during weeks 4 and 5 and then decreased sharply to week 6. The mean dry weight of the IJ dropped at a roughly constant rate from an initial level of 74 ng/IJ to 41 ng/IJ at week 6. Thus, during the period of 6 weeks at 28°C, each IJ consumed nearly half of its initial dry weight. Consumption of the lipids, proteins, glycogen and trehalose accounted for 91, 41, 56 and 78% of the initial levels of these compounds and 47, 41, 9 and 3% of the total dry weight of materials consumed, respectively. Most lipids were consumed in the first 3 weeks while most proteins, glycogen and trehalose were consumed in the last 2 or 3 weeks. Oxygen consumption rate decreased from 3.0 to 0.5 ml/million IJ/day from day 1 to week 6 while the respiratory quotient remained constant at about 0.7 for the first 4 weeks then dropped sharply to 0.3 at week 6. Both survival time and the rate of reduction in mean dry weight of IJ were severely affected by temperature and buffering. The functions of the individual energy reserve materials, characteristics of the energy metabolism and the relationship between energy metabolism and the survival and infectivity of the IJ are discussed. Der Energiestoffwechsel und seine Beziehung zum Uberleben und zur Infektivitat der Infektionsjuvenilen von Steinernema carpocapsae unter aeroben Bedingungen - Der Energiestoffwechsel der Infektionsjuvenilen (IJ) von Steinernema carpocapsae unter aeroben Bedingungen und seine Beziehungen zum Uberleben und zur Infektivitat der IJ wurde untersucht durch die Erfassung der Anderungen im mittleren Trockengewicht, des Niveaus der wichtigen Energiereservestoffe, des Sauerstoffverbrauchs, des Respirationsquotienten sowie der Uberlebensrate und der Infektivitat frisch gewonnener IJ, die in Leitungswasser bei 28°C auf einem Schuttler gehalten wurden. Die Uberlebensrate uberschritt wahrend der ersten sechs Wochen 90% und fiel dann in der achten Woche schnell auf etwa 50% ab. Die Infektivitat anderte sich innerhalb der ersten 3 Wochen wenig, fiel dann im Laufe der Wochen 4 und 5 etwas ab, verminderte sich dann aber schnell in Woche 6. Das mittlere Trockengewicht der IJ fiel ungefahr gleichmasig von einem Ausgangsniveau von 74 ng/IJ auf 41 ng/IJ in Woche 6 ab. Jedes IJ verbrauchte also bei 28°C innerhalb von 6 Wochen fast die Halfte seines ursprunglichen Trockengewichts. Vom ursprunglichen Gehalt an Lipiden wurden 91% verbraucht, von Proteinen 41%, von Glykogen 56% und von Trehalose 78%. Vom Gesamtverbrauch entfielen 47% auf Lipide, 41% auf Proteine, 9% auf Glykogen und 3% auf Trehalose. Die meisten Lipide wurden in den ersten drei Wochen verbraucht, wahrend die meisten Proteine, Glykogen und Trehalose in den letzten 2 oder 3 Wochen verbraucht wurden. Der Sauerstoffverbrauch fiel von 3,0 auf 0,5 ml/million IJ/Tag von Tag 1 bis Woche 6, wahrend der Respirationsquotient in den ersten 4 Wochen konstant bei 0,7 und dann schnell auf 0,3 in Woche 6 abnahm. Uberlebensdauer und Abnahme des mittleren Trockengewichts wurden durch Temperatur und Pufferung stark beeinflusst. Die Funktionen der einzelnen Energiereservestoffe, die Kennzeichen des Energiestoffwechsels und die Beziehungen zwischen Energiestoffwechsel, Uberleben und Infektivitat der IJ werden diskutiert.

Permeability of the infective juveniles of Steinernema carpocapsae to glycerol during osmotic dehydration and its effect on biochemical adaptation and energy metabolism

Permeability of the sheath and cuticle of the infective juveniles (IJs) of Steinernema carpocapsae to glycerol and its effect on biochemical adaptation of the IJs to osmotic dehydration were examined by incubating both sheathed and exsheathed IJs in glycerol-d5 solution then monitoring the changes in levels of deuterium labelled and non-labelled glycerol and trehalose. Energy metabolism of the IJs during osmotic dehydration and subsequent rehydration and the effect of the permeated glycerol on this process were investigated by examining and comparing the changes in mean dry weight and key biochemical composition of the IJs dehydrated in glycerol and sodium chloride solutions. The results show: (1) similarly to evaporative dehydration, osmotic dehydration induces IJs to synthesise the protectants glycerol and trehalose; (2) glycerol permeates the sheath and the cuticle into the body of IJs during dehydration in glycerol solution. Part of the permeated glycerol plays a role as protectant like that synthesised by IJs from their energy reserve materials while part is incorporated into trehalose; (3) the sheath reduces the rate of permeation of glycerol and therefore affects the equilibrium glycerol and trehalose levels of the IJs and also the time needed to reach the equilibrium levels; (4) the reduction in mean dry weight and lipids of the IJs during dehydration in glycerol solution is substantially less than those dehydrated in sodium chloride solution. Both the total protectant level and the ratio of glycerol to trehalose of the IJs dehydrated in glycerol solution are higher than those dehydrated in sodium chloride solution; (5) glycogen reserves of the IJs play a role as a buffer reservoir of the protectants during both dehydration and rehydration but the principal sources of the protectants during dehydration are more likely to be lipids and proteins rather than glycogen.

Characteristics of protectant synthesis of infective juveniles of Steinernema carpocapsae and importance of glycerol as a protectant for survival of the nematodes during osmotic dehydration.

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.

Biology of the bark beetle Ips grandicollis Eichhoff (Coleoptera: Scolytinae) and its arthropod, nematode and microbial associates: a review of management opportunities for Australia.

The five‐spined bark beetle, Ips grandicollis, is an exotic pest in Australia that preferentially attacks stressed pine trees, including Pinus radiata D. Don, but it can also attack healthy trees. The beetle has been present in Australia for 70 years, feeding principally on logging debris, with occasional outbreaks resulting in damage to plantations. Attack on trees stressed by drought, fire or storm damage leads to occasional significant losses. In recent years, I. grandicollis has been observed to attack ‘trap trees’ treated with herbicide to make them attractive to Sirex noctilio Fabricius as part of a successful biological control programme against this wood wasp. Ips grandicollis is able to tolerate a wide range of climatic conditions, and has an extensive geographical range (limited by host tree plantings). The economic impact of I. grandicollis is exacerbated by adults vectoring a fungus, Ophiostoma ips (Rumbold) Nannfeldt, which discolours the outer sapwood and contributes to tree death. Nematodes also are also associated with I. grandicollis, both in the body cavity and under the elytra. The dominant nematode is Contortylenchus grandicolli Massey, which is found internally, in haemocoel, the gut and the head region of the majority of adult beetles. Mites and bacteria are also associated with I. grandicollis but their biology is not well known. Since the first detection of I. grandicollis in Australia, various bio‐control and other management strategies have been tested. While a better understanding of the microbial and nematode associates of I. grandicollis may yield novel approaches for the management of this exotic pest, semiochemical‐based disruptants offer more immediate scope, particularly for protecting small areas of high value trees such as trap tree plots.

Using deuterium as an isotopic tracer to study the energy metabolism of infective juveniles of Steinernema carpocapsae under aerobic conditions.

Changes in survival, mean dry weight, levels of key energy reserve compounds and respiration of non-feeding infective juveniles (IJs) of Steinernema carpocapsae incubated in various ratios of D2O/H2O on a shaker at 28 degrees C were determined. Patterns of deuterium distribution in trehalose, glycogen and key fatty acids of the IJs incubated in 50% (v/v) D2O/H2O were also examined. The rates of decline in mean dry weight and lipid levels of IJs incubated in D2O/H2O were proportional, while the survival times of IJs were inversely proportional, to the ratio of D2O/H2O. Deuterium was randomly and extensively incorporated into the C-H bonds of trehalose and glycogen but was barely incorporated in fatty acid moieties of the IJs. The changes in the patterns and the extents of deuterium incorporation, as well as the levels of trehalose, glycogens and fatty acids during the experimental period indicate that: (1) The lipogenesis pathway is not functioning in the Ijs. (2) Trehalose and glycogen are constantly consumed and replenished and they are mainly derived from lipids. (3) Futile cycles involving trehalose and glycogen, which enable IJs to regulate the levels of these two compounds more effectively, may exist. The results support the view that lipids are the primary energy reserve of the IJs while trehalose, glycogen and proteins can be used for energy generation, even though this is not their primary role.