Interactions between imidacloprid and Metarhizium brunneum on adult Asian longhorned beetles (Anoplophora glabripennis (Motschulsky)) (Coleoptera: Cerambycidae)

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), a longhorned beetle species native to Asia, has been introduced into several North American and European cities. Currently eradication and preventive measures are limited to identifying and destroying infested trees and protecting uninfested trees with trunk or soil-injections of the systemic insecticide imidacloprid. Because entomopathogenic fungi like Metarhizium brunneum Petch have been identified as virulent against these beetles we conducted several tests to determine the compatibility of the two agents in combination. Radial hyphal growth and the sporulation capacity of M. brunneum on Sabouraud dextrose agar with yeast were not significantly affected by the presence of imidacloprid. In a 2 × 3 factorial experiment investigating interactions between exposure to imidacloprid and M. brunneum we observed no effect of imidacloprid alone on beetle survival when beetles were given a single dose of 10 or 100 ppm compared to control insects. We observed a significant effect of exposure to M. brunneum, and a significant interaction between imidacloprid and M. brunneum representing a synergistic effect of dual treatment. Beetles exposed to the fungus alone lived significantly longer compared to insects treated with a single dose of 100 ppm imidacloprid (9.5 vs. 6.5 d). Consumption of striped maple twigs by beetles exposed to imidacloprid, across concentrations, was reduced 48% compared to control insects, where as consumption by M. brunneum-exposed beetles was reduced by 16% over the first 6-days of the test period. Beetles fed 100 ppm imidacloprid consumed 32% less over the first 3 d compared to beetles not exposed to imidacloprid and thereafter consumed as much as beetles not fed 100 ppm imidacloprid. M. brunneum-exposed beetles consumed significantly less food than control insects throughout the test period, and beetles treated with imidacloprid produced significantly fewer conidia compared to beetles not treated with imidacloprid.     

Parasite altered micro-distribution of Gammarus pulex (Crustacea: Amphipoda)

In a river survey, Gammarus pulex amphipods both unparasitised and parasitised with the acanthocephalan Echinorhynchus truttae were distributed similarly with respect to flow regimen, tending to be more abundant in faster, shallower, riffle patches. However, there was a higher prevalence of parasitism in faster, shallower areas than in slower, deeper areas and abundance correlated with macrophyte coverage for unparasitised but not parasitised amphipods, indicating subtle differences in habitat usage. A laboratory 'patch' simulation indicated that parasitism influenced micro-distribution. There were higher proportions of unparasitised amphipods in/under stone substrates and within weed. In contrast, there were higher proportions of parasitised amphipods in the water column and at the water surface. As the experiment progressed, unparasitised but not parasitised amphipod habitat usage shifted from those micro-habitats above the substrate and in the water column to those in/under the substrates. Experiments also demonstrated that parasitised amphipods were more active and had a greater preference for illumination. Previous studies of the effects of acanthocephalan parasitism of amphipod hosts have focussed on how drift behaviour is altered, now we show that subtle differences in micro-habitat usage could translate to greatly increased vulnerability to fish predation. We discuss how aggregation of parasitised individuals within specific habitats could promote parasite transmission.     

Parasite transmission and cannibalism in an amphipod (Crustacea)

In its freshwater amphipod host Gammarus duebeni celticus, the microsporidian parasite Pleistophora mulleri showed 23% transmission efficiency when uninfected individuals were fed infected tissue, but 0% transmission by water-borne and coprophagous routes. Cannibalism between unparasitised and parasitised individuals was significantly in favour of the former (37% compared to 0%). In addition, cannibalism between parasitised individuals was significantly higher than between unparasitised individuals (27% compared to 0%). Thus, parasitised individuals were more likely to be cannibalised by both unparasitised and parasitised individuals. We discuss the conflicting selective forces within this host/parasite relationship, the implications of parasite mediated cannibalism for host population structure and the impacts this may have on the wider aquatic community.     

Phospholipase C is required for the control of stomatal aperture by ABA

The calcium-releasing second messenger inositol 1,4,5-trisphosphate is involved in the regulation of stomatal aperture by ABA. In other signalling pathways, inositol 1,4,5-trisphosphate is generated by the action of phospholipase C. We have studied the importance of phospholipase C in guard cell ABA-signalling pathways. Immunolocalisation of a calcium-activated phospholipase C confirmed the presence of phospholipase C in tobacco guard cells. Transgenic tobacco plants with considerably reduced levels of phospholipase C in their guard cells were only partially able to regulate their stomatal apertures in response to ABA. These results suggest that phospholipase C is involved in the amplification of the calcium signal responsible for reductions in stomatal aperture in response to ABA. As full ABA-induced inhibition of stomatal opening was not observed, our results support a role for the action of other calcium-releasing second messengers in the guard cell ABA-signalling pathway. It is not known whether these different calcium-releasing second messengers act in the same or parallel ABA-signalling pathways.     

The NO pathway acts late during the fertilization response in sea urchin eggs

Both the inositol 1,4,5-trisphosphate (InsP(3)) and ryanodine receptor pathways contribute to the Ca(2+) transient at fertilization in sea urchin eggs. To date, the precise contribution of each pathway has been difficult to ascertain. Evidence has accumulated to suggest that the InsP(3) receptor pathway has a primary role in causing Ca(2+) release and egg activation. However, this was recently called into question by a report implicating NO as the primary egg activator. In the present study we pursue the hypothesis that NO is a primary egg activator in sea urchin eggs and build on previous findings that an NO/cGMP/cyclic ADP-ribose (cADPR) pathway is active at fertilization in sea urchin eggs to define its role. Using a fluorescence indicator of NO levels, we have measured both NO and Ca(2+) at fertilization and establish that NO levels rise after, not before, the Ca(2+) wave is initiated and that this rise is Ca(2+)-dependent. By inhibiting the increase in NO at fertilization, we find not that the Ca(2+) transient is abolished but that the duration of the transient is significantly reduced. The latency and rise time of the transient are unaffected. This effect is mirrored by the inhibition of cGMP and cADPR signaling in sea urchin eggs at fertilization. We establish that cADPR is generated at fertilization, at a time comparable to the time of the rise in NO levels. We conclude that NO is unlikely to be a primary egg activator but, rather, acts after the initiation of the Ca(2+) wave to regulate the duration of the fertilization Ca(2+) transient.