Susceptibility of different developmental stages of the root-knot nematode, Meloidogyne incognita, to the nematicide oxamyl

Oxamyl (6.25 μg ml^-1 soil water) was applied to cucumber roots containing Meloidogyne incognita at different stages of nematode development. Oxamyl was more effective in reducing the proportion of juveniles which developed into females when applied soon after infection to second stage juveniles than when applied later (to third and fourth stage juveniles). Early application of oxamyl also significantly reduced the proportion of females with egg masses, whereas late application had no such effect. However, the number of eggs per egg mass and the size of the young adult females was significantly reduced by all oxamyl treatments - the earlier the application the greater the effect. These results support the hypothesis that actively feeding second stage juveniles of Meloidogyne spp. are more susceptible to systemic nematicides than are the non-feeding third and fourth stage juveniles.     

Effects of the nematicide oxamyl on life cycle stages of Globodera rostochiensis

Hatched second stage juveniles of Globodera rostochiensis were found to be more sensitive than either unhatched juveniles or adult males to low concentrations of oxamyl (EC₅₀ value for activity 0.5 μg oxamyl ml^-1). Development of juveniles in roots was significantly inhibited by 2.0 μg oxamyl ml^-1 probably due to impairment of normal feeding activity. The behavioural events necessary for orientation of juveniles towards roots for invasion and orientation of males towards females for fertilisation were found to be impaired by 0.5 and 1.0 μg oxamyl ml^-1 respectively. A comparison with previous work on Meloidogyne incognita showed G. rostochiensis juveniles to be more sensitive to oxamyl.     

The application of ecological theory to palaeoecological studies, with special reference to equilibrium theory and the Ordovician System

In the light of recent applications of equilibrium theory to palaeoecological investigation, the origins and scope of the model are reviewed as a perspective for considering the viability of such applications in the analysis of Ordovician faunal associations. Alternative methods for the detection of immigration and emigration patterns are advanced in favour of other recently proposed techniques. The mid-Caradoc Gelli-grin Formation is used as an example of a well sampled fossiliferous deposit from which comprehensive faunal data can be derived for use in the detection of intra-association fluctuations in faunal composition. Different methods of defining such fluctuations are shown to produce consistent results. 'Saturation', 'area effect' and 'overshoot effect' are all shown to be aspects of equilibrium theory with potential for application in the palaeoecological field. The calculation of the coefficient of variation for eight faunal associations discussed here is shown to be a useful method for the determination of the degree of saturation of such associations; comparable associations show similar saturation values.     

Behaviour of the systemic nematicide oxamyl in plants in relation to control of invasion and development of Meloidogyne incognita

A single foliar application of oxamyl (12.5 μg) in acetone significantly reduced invasion of cucumber seedlings by Meloidogyne incognita juveniles for at least 21 days but did not affect the early stages of development of juveniles which had already invaded the roots. In contrast, application of oxamyl to the roots significantly reduced both invasion and development of juveniles. Concurrent studies using radiolabelled oxamyl showed that the amount of toxicant in the roots after 3 days was 13 times greater following root application than after foliar treatment. It is probable that oxamyl concentrates at the sites of nematode attack as an overall concentration of only 3 ng oxamyl g^-1 root was sufficient to prevent invasion. Much greater concentrations than this were required to affect the nematode in vitro. Oxamyl appeared to be lost from the roots into the soil principally in the form of its non-toxic oxime and it is suggested that the site of action following foliar application is at the root surface or outer cortex. Studies on the invasion behaviour of M. incognita juveniles on agar showed that the action of oxamyl had a sensory component.     

A theory for the chemical mediation of the excitability of the brain, with special reference to natural and drug-induced sleep.

We review evidence which suggests to us that uracil, or a molecule structurally resembling uracil, is likely to be involved in the mediation of level of arousal. In addition we attempt to show that at least one theory, based on this idea, provides a molecular mechanism for certain features of natural sleep, and for the effect on arousal of several classes of drugs and of certain gene mutations. This theory, and related ones, can feasibly be tested further with existing methods.     

Carbon dioxide for euthanasia: concerns regarding pain and distress, with special reference to mice and rats

Carbon dioxide (CO2) is the most commonly used agent for euthanasia of laboratory rodents, used on an estimated tens of millions of laboratory rodents per year worldwide, yet there is a growing body of evidence indicating that exposure to CO2 causes more than momentary pain and distress in these and other animals. We reviewed the available literature on the use of CO2 for euthanasia (as well as anaesthesia) and also informally canvassed laboratory animal personnel for their opinions regarding this topic. Our review addresses key issues such as CO2 flow rate and final concentration, presence of oxygen, and prefilled chambers (the animal is added to the chamber once a predetermined concentration and flow rate have been reached) versus gradual induction (the animal is put into an empty chamber and the gas agent(s) is gradually introduced at a fixed rate). Internationally, animal research standards specify that any procedure that would cause pain or distress in humans should be assumed to do so in non-human animals as well (Public Health Service 1986, US Department of Agriculture 1997, Organization for Economic Cooperation and Development 2000). European Union guidelines, however, specify a certain threshold of pain or distress, such as 'skilled insertion of a hypodermic needle', as the starting point at which regulation of the use of animals in experimental or other scientific procedures begins (Biotechnology Regulatory Atlas n.d.). There is clear evidence in the human literature that CO2 exposure is painful and distressful, while the non-human literature is equivocal. However, the fact that a number of studies do conclude that CO2 causes pain and distress in animals indicates a need for careful reconsideration of its use. Finally, this review offers recommendations for alternatives to the use of CO2 as a euthanasia agent.