Population modelling of Varroa jacobsoni Oud

To understand population dynamics of the mite Varrroa jacobsoni and to enable computer simulations, Fries et al. [Bee World 75 (1994) 5-28] incorporated available knowledge into a mite population model. In this paper, we update and extend this model by incorporating more recent data, in particular on mite invasion from bees into brood cells. By predicting invasion into and emergence from brood cells, the model proves to be useful to evaluate the effects of changes in model parameters on the mite population when the distribution of mites over bees and brood are important. The model predicts that a longer brood rearing period dramatically increases the mite population size and that a relatively larger number of drone brood cells leads to an increased population growth. As mite control treatments often only affect mites either in brood cells or on adult bees, the model can be used to evaluate their effectiveness and timing. The model indicates that changes in parameters that affect the reproductive success of the mites in brood cells have a large impact on the mite population. © Inra/DIB/AGIB/Elsevier, Pari

REACTIVITY OF CHLOROPHYLL a/b-PROTEINS AND MICELLAR TRITON X-100 COMPLEXES OF CHLOROPHYLLS a OR b WITH BOROHYDRIDE

The reaction of several plant chlorophyll-protein complexes with NaBH4 has been studied by absorption spectroscopy. In all the complexes studied, chlorophyll b is more reactive than Chi a, due to preferential reaction of its formyl substituent at C-7. The complexes also show large variations in reactivity towards NaBH4 and the order of reactivity is: LHCI > PSII complex > LHCII > PSI > P700 (investigated as a component of PSI). Differential pools of the same type of chlorophyll have been observed in several complexes. Parallel work was undertaken on the reactivity of micellar complexes of chlorophyll a and of chlorophyll b with NaBH4 to study the effect of aggregation state on this reactivity. In these complexes, both chlorophyll a and b show large variations in reactivity in the order monomer > oligomer > polymer with chlorophyll b generally being more reactive than chlorophyll a. It is concluded that aggregation decreases the reactivity of chlorophylls towards NaBH4 in vitro, and may similarly decrease reactivity in naturally-occurring chlorophyll-protein complexes

Herbivores enable plant survival under nutrient limited conditions in a model grazing system

We make a theoretical study of nitrogen cycling in a model of a grazing system with five compartments. The rates of uptake of nutrient by plants and herbivores are allowed nonlinear forms which involve no a priori assumptions about whether the system is subject to top-down or bottom-up control. We derive a method of piecewise linear approximation which allows analytical study of the system. We then use this method to investigate the properties of the equilibrium states of the system, and in particular whether the system favours donor- or recipient-control, the grazing optimization problem, and the potential benefits of herbivory to plant growth. We are able to generalise our results to all uptake functions of the same qualitative class as those considered, and to show that in general the system will tend to a stable equilibrium state of donor-controlled herbivory. In this model, the presence of the ‘right’ class of herbivore is not only beneficial to plant growth in certain circumstances, but can be essential to their survival, allowing plants to co-exist with herbivores under conditions in which they would be unable to survive alone.17 page(s