Aggregation and a strong Allee effect in a cooperative outbreak insect.

Most species that are negatively impacted when their densities are low aggregate to minimize this effect. Aggregation has the potential to change how Allee effects are expressed at the population level. We studied the interplay between aggregation and Allee effects in the mountain pine beetle (Dendroctonus ponderosae Hopkins), an irruptive bark beetle that aggregates to overcome tree defenses. By cooperating to surpass a critical number of attacks per tree, the mountain pine beetle is able to breach host defenses, oviposit, and reproduce. Mountain pine beetles and Hymenopteran parasitoids share some biological features, the most notable of which is obligatory host death as a consequence of parasitoid attack and development. We developed spatiotemporal models of mountain pine beetle dynamics that were based on the Nicholson-Bailey framework but which featured beetle aggregation and a tree-level attack threshold. By fitting our models to data from a local mountain pine beetle outbreak, we demonstrate that due to aggregation, attack thresholds at the tree level can be overcome by a surprisingly low ratio of beetles per susceptible tree at the stand level. This results confirms the importance of considering aggregation in models of organisms that are subject to strong Allee effects.

Chirality of methamphetamine and amphetamine from workplace urine samples.

Several positive methamphetamine/amphetamine urine samples were reexamined to determine the chirality of the detected drug or drugs. (S)-N-(Trifluoroacetyl)prolyl derivatives were prepared and analyzed using GC/MS. In one case, pure d-isomers of methamphetamine and amphetamine were detected. In the remainder of the samples involving both drugs, skewed racemates were detected, with the l-isomer of methamphetamine and the d-isomer of amphetamine predominating slightly over their enantiomers. In samples involving amphetamine only, 50:50 mixtures of d- and l-isomers were detected. In no instance was pure i-methamphetamine (from a Vicks inhaler) detected.

Use of erythrocyte fragility profiles for monitoring immune-mediated haemolysis in horses.

The fragility of erythrocytes is easily demonstrated by their ability to withstand osmotic swelling and lysis in solutions of increasingly hypotonic saline. In healthy animals a plot of percentage haemolysis against increasing hypotonicity produces a sigmoid curve. Using the same data a derivative curve calculated from haemolytic increments shows a normal distribution of fragility within samples. In enhanced fragility due to immune-mediated haemolytic anaemia, these profiles of haemolysis are markedly altered and the derivative curve becomes multiphasic, indicating the presence of subpopulations of erythrocytes with differing fragility ranges. Analysis of these profiles in a case of intravascular immune-mediated haemolysis in a horse provided useful graphic information for diagnosis and prognosis. In particular, the size of the subpopulation showing increased fragility could be assessed in the acute phase and monitored during recovery.