Genotypic differences in the growth of bananas (Musa spp.) infected with migratory endoparasitic nematodes. 1. Roots

The effects of nematodes on root morphology and the association of root characteristics with resistance to nematodes of seven banana varieties were investigated in two experiments. Banana plants were grown in controlled conditions within polytunnels and harvested on three occasions for the measurement of root morpholopy, and biomass. Varieties differed in their resistance to nematodes, from resistant (Yg Km5, FHIA 17, FHIA 03) and partly resistant (FHIA 01, FHIA 25) to not resistant ((FHIA 23, Williams). Nematodes reduced the root dry weight of FHIA 01, FHIA 17 and FHIA 23 at some harvests. Primary root number was on average 9.5% lower in nematode-infected plants than controls, with no differences among the varieties. Thus, there was no simple association between the resistance of these varieties and their tolerance to nematodes. Varieties differed in root morphology. Root dry weight was greatest for resistant varieties Yg Km5 and FHIA 03, and least for non-resistant varieties FHIA 23 and Williams. Thus, resistance to nematodes was associated with varieties with greater root mass and more and larger primary roots.

Genotypic differences in the growth of bananas (Musa spp.) infected with migratory endoparasitic nematodes. 2. Shoots

In order to identify the effect of burrowing nematodes on the shoots (pseudostem and leaves) of banana plants and to determine whether or not shoot characteristics are associated with plant resistance to nematodes two experiments were conducted in controlled conditions within polytunnels. The banana plants were harvested on three occasions for the measurement of root morphology and biomass. Varieties differed in their resistance to nematodes from resistant (Yg Km5, FHIA 17, FHIA 03) and partly resistant (FHIA 01, FHIA 25) to not resistant (FHIA 23, Williams). Nematodes reduced total plant dry weight at the first harvest in Experiment 1 and by an average of 8.8% in Experiment 2, but did not affect leaf area in either experiment. The ratio of above-ground Weight to total plant weight was reduced from 75% to 72% in nematode-infected plants compared with the control plants for all varieties tested in Experiment 1, but was only reduced in FHIA 25 and FHIA 23 in Experiment 2. Varieties differed in above-ground growth. The FHIA varieties had greater shoot weights and leaf area than YgKm5 and Williams. Overall, resistance to nematodes was associated with the partitioning of a greater proportion of biomass to the roots than to above-ground parts.

Influence of temperature on the production and infectivity of entomopathogenic nematodes against larvae and pupae of vine weevil, Otiorhynchus sulcatus, (Coleoptera: Curculionidae)

Susceptibility of late instar vine weevil Otiorhynchus sulcatus larvae and pupae to four species entomopathogenic nematodes were tested. Bioassays on production and infectivity to larvae and pupae were compared for two steinernematids and two heterorhabditis such as Steinernema carpocapsae, S. feltiae, Heterorhabditis indica and H. bacteriophora. Nematodes production of all species was determined by the number infective juveniles (IJs) established in vine weevil larvae and pupae O. sulcatus using sand and filter paper bioassay. S. feltiae produced the maximum number in larvae and pupae at 20°C as compared to other nematodes but production of H. indica, was better at 25°C in larvae and pupae followed by H. bacteriophora, S. carpocapsae and Infectivity test of larvae and pupae was also done in sand media. Infective juveniles recovered from larvae and pupae when infected with S. feltiae produced maximum infective juveniles at 20°C temperatures than all other isolates. H. bacteriophora produced higher number of IJs in larvae and pupae than all other nematode isolates at 25°C. This paper indicates the application of nematodes with the knowledge of insect pest biology represents a possible new strategy for O. sulcatus larvae and pupae.

A comparative study on the effectiveness of laboratory bioassays of entomopathogenic nematodes against desert locust nymphs Schistocerca gregaria (Acrididae:Orthoptera)

Entomopathogenic nematodes, Steinernema carpocapsae, S. feltiae (Steinernematids) Heterorhabditis indica and H. bacteriophora (Heterorhabditids) were studied to control nymphs of desert locust Schistocerca gregaria. Results of all experiments showed a significant difference in mortality percentage among all isolates. All nematodes were found more effective when exposure time was increased up to 10 days. On the other hand, both Heterorhabditids caused maximum mortality as compared to Steinernematids at 30 degree C. When different moisture levels were tested in the sand arena, a medium level of moisture (1%) caused maximum insect mortality in all isolates. However, highest concentration of each isolate (200 IJs per ml) proved to be most appropriate for maximum insect death. Similarly, both Heterorhabditis nematodes when orally applied to insects killed maximum nymphs as compared to other two Steinernematids. A similar response was observed in infectivity test when maximum percentage of IJs of both isolates of Heterorhabditis successfully penetrated into the body of locust nymphs. This research suggests some useful basic findings in developing biocides with suitable virulent of entomopathogenic nematode for controlling nymphs of desert locust.

Effects of forage source and soybean and marine algal oil supplementation on milk fatty acid composition in ewes

The objective of the present studies was to determine effects of basal dietary forage source on the response of milk fatty acid composition to an oil supplement based (2:1, respectively, w/w) on soybean oil and marine algae biomass oil high in cis-9, cis-12 C18:2n − 3 and C22:6n − 3, respectively. In Study 1, Hampshire × Dorset ewes (48) were randomly assigned to one of four treatments and 12 pens in a completely randomized design blocked on the basis of lambing date and number of lambs suckled. Control rations (60:40 forage:concentrate, dry matter (DM) basis) based on alfalfa pellets (AP) or corn silage (CS) were fed from lambing. Beginning at 22 days postpartum, three pens of ewes fed AP and three pens of ewes fed CS were supplemented with oil (30 g/kg of ration DM) in place of corn meal. Average ewe DM intake (DMI) and average daily gain (ADG) were measured weekly. Milk yield and composition were measured at 42 days postpartum. DMI was lower (P<0.02) for CS and for oil, but milk yield was not affected by forage source or oil supplementation. Milk fat content was higher for oil (P<0.10) and milk protein content was higher for AP (P<0.04). Total CLA concentration (g/100 g fatty acids) increased (P<0.01) with CS and oil, and the response to oil was greater for AP (P<0.04). Similarly, total trans-C18:1 and C22:6ω−3 concentrations were higher for CS and oil, but the response to oil was greater for CS (P<0.06 and P<0.01, respectively). In Study 2, the experiment was repeated using alfalfa haylage (AH) instead of AP. The DMI decreased (P<0.05) with oil feeding, but was not affected by forage source. Milk yield was decreased by feeding oil with AH, but not by feeding oil with CS (P<0.03). Milk fat content tended to be increased by feeding oil with AH, but tended to be decreased by feeding oil with CS (P<0.08). Total CLA concentration was increased (P<0.01) for AH versus CS and by oil, and the response to oil supplementation was greater for AH (P<0.01). In contrast, total trans-C18:1 concentration was higher for CS versus AH, with a greater response to oil for CS (P<0.05). Feeding marine oil increased the C22:6ω−3 (P<0.01) concentration, and the response was greater for AH (P<0.04). To further characterize the response of milk fat composition to dietary oil in ewes, a third study used six pens of three ewes each assigned to either the control CS diet used for Study 2 or the same diet supplemented with 45 g/kg (DM basis) of the oil mixture. Feeding oil had no effect on DMI, milk yield or milk fat concentration, but again increased (P<0.001) total trans-C18:1 and C22:6ω−3 concentrations and numerically increased (114%) total CLA concentration. Milk fatty acid composition responses to supplemental vegetable and marine oils were affected by forage source. Milk trans-C18:1 concentration was higher when CS was fed in Studies 1 and 2, but the effect of forage species on CLA concentration differed between studies, which may reflect differences in diet PUFA content and consumption, as well as amounts of dietary starch and fiber consumed. Despite large increases in trans-C18:1 concentration, milk fat content was not decreased by feeding unsaturated oils to ewes, even at diet levels of 45 g/kg of ration DM.

Facultative scavenging as a survival strategy of entomopathogenic nematodes

Entomopathogenic nematodes cannot be considered only as parasitic organisms. With dead Galleria mellonella larvae, we demonstrated that these nematodes use scavenging as an alternative survival strategy. We consider scavenging as the ability of entomopathogenic nematodes to penetrate, develop and produce offspring in insects which have been killed by causes other than the nematode-bacteria complex. Six Steinernema and two Heterorhabditis species scavenged but there were differences among them in terms of frequency of colonisation and in the time after death of G. mellonella larvae that cadavers were penetrated. The extremes of this behaviour were represented by Steinernema glaseri which was able to colonise cadavers which had been freeze-killed 240 h earlier and Heterorhabditis indica which only colonised cadavers which had been killed up to 72 h earlier. Also, using an olfactometer, we demonstrated that entomopathogenic nematodes were attracted to G. mellonella cadavers. (c) 2007 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

Scavenging or infection? Possible host choosing by entomopathogenic nematodes

Entomopathogenic nematodes are able to survive by scavenging. We tested Steinernema feltiae, S. affine and Heterorhabditis megidis alone or in different combinations to evaluate the responses of these nematodes when dead or live Galleria mellonella larvae were offered. Steinernema feltiae and S. affine scavenged upon dead G. mellonella larvae and about 30% more dead larvae were penetrated than live ones. By contrast, H. megidis penetrated more live larvae than dead ones. When the nematode species were combined, the results varied among the combinations, but the dead larvae were always used as a host. The behaviour of natural field populations of S. feltiae and S. affine was also compared. Steinernema feltiae showed no difference between scavenging and performing 'normal infections', whereas S. affine scavenged to a reduced amount (around 60% less); this difference could be related to the particular foraging strategy of these nematodes.

The control of root-knot nematodes (Meloidogyne spp.) by Pseudomonas oryzihabitans and its immunological detection on tomato roots

Pseudomonas oryzihabitans, a bacterium associated with the entomopathogenic nematode Steinernema abbasi, was evaluated for its potential to colonise roots and thereby control a field population of root-knot nematodes. Immunological techniques were developed to detect root colonisation of P. oryzihabitans on tomato roots using a specific polyclonal antibody raised against vegetative bacterial cells. In vitro, bacterial cell filtrates were also shown significantly to inhibit juveniles hatching. In a glasshouse pot experiment, there were 22 and 82% fewer females in roots of plants treated with suspensions containing 10(3) and 10(6) cells ml(-1) of P oryzihabitans, respectively. In addition, there were significantly fewer egg masses produced; however, the numbers of eggs per egg mass did not differ significantly. The relationship between root colonisation and nematode control is discussed.

Genotypic sex determination enabled adaptive radiations of extinct marine reptiles

Adaptive radiations often follow the evolution of key traits, such as the origin of the amniotic egg and the subsequent radiation of terrestrial vertebrates. The mechanism by which a species determines the sex of its offspring has been linked to critical ecological and life-history traits(1-3) but not to major adaptive radiations, in part because sex-determining mechanisms do not fossilize. Here we establish a previously unknown coevolutionary relationship in 94 amniote species between sex-determining mechanism and whether a species bears live young or lays eggs. We use that relationship to predict the sex-determining mechanism in three independent lineages of extinct Mesozoic marine reptiles (mosasaurs, sauropterygians and ichthyosaurs), each of which is known from fossils to have evolved live birth(4-7). Our results indicate that each lineage evolved genotypic sex determination before acquiring live birth. This enabled their pelagic radiations, where the relatively stable temperatures of the open ocean constrain temperature-dependent sex determination in amniote species. Freed from the need to move and nest on land(4,5,8), extreme physical adaptations to a pelagic lifestyle evolved in each group, such as the fluked tails, dorsal fins and wing-shaped limbs of ichthyosaurs. With the inclusion of ichthyosaurs, mosasaurs and sauropterygians, genotypic sex determination is present in all known fully pelagic amniote groups (sea snakes, sirenians and cetaceans), suggesting that this mode of sex determination and the subsequent evolution of live birth are key traits required for marine adaptive radiations in amniote lineages.

Litomosoides sigmodontis: vaccine-induced immune responses against Wolbachia surface protein can enhance the survival of filarial nematodes during primary infection

Wolbachia are bacteria present within the tissues of most filarial nematodes. Filarial nematode survival is known to be affected by immune responses generated during filarial nematode infection and immune responses to Wolbachia can be found in different species harbouring filarial nematode infections, including humans. Using the rodent filarial model Litomosoides sigmodontis, we show that pre-exposure to wolbachia surface protein in a Th1 context (but not in a Th2-context) enhances worm survival on subsequent challenge. This study suggests that despite abundant evidence that pro-inflammatory reactions to the endosymbiont have detrimental effects on the both the nematode and mammalian host, they may under some circumstances be beneficial to the nematode.