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Foraging parasitoid females should preferentially oviposit on hosts most suitable for progeny development to maximize their fitness. However, the introduction of a new host species may disrupt the link between the reliability of the cues and the expected adaptive outcome of female choice, leading to an evolutionary trap. This mismatch between behavioural acceptance and lack of development exists for North American and European egg parasitoids (Scelionidae) that encounter invasive Halyomorpha halys in areas where this exotic host has recently established. To explain this mismatch, we utilized an L9 orthogonal array design to assess and rank the influence of several critical factors characterizing host resource (host species, egg age, egg status, and surface wash) on behaviour (acceptance, patch residence and patch exploitation) and development of North American native Trissolcus euschisti egg parasitoid. Our results indicate that the host egg age is most important for behaviour, but is least influential for development of the progeny. This study suggests that the maladaptive decision to oviposit in an unsuitable host is due to a mismatch between the cues that females use, and the subsequent expected outcome of this choice. Therefore, it is the relative importance of individual factors when assessed simultaneously that influences the decision-making of female parasitoids.

Invasive species can destabilize ecological communities by becoming novel hosts, prey, predators or competitors for native species. They can have lasting effects on population dynamics when they reduce the fitness of native individuals. The establishment and spread of invasive Halyomorpha halys, in Europe and North America, have presented native natural enemies in the introduced areas with such a challenge. The native parasitoids readily parasitize eggs of H. halys, but their progeny rarely develops in fresh eggs of this host. The barriers to successful development of native parasitoids in H. halys eggs remain unidentified, and the affected developmental processes therein remain unclear. To determine the timing of failed development of native parasitoids in fresh H. halys eggs, we examined the temporal development of the Trissolcus euschisti parasitoid within suitable (Podisus maculiventis) and unsuitable (Halyomorpha halys) host eggs using a DNA barcode-based approach, and in situ 3D visualization by X-ray micro-computed tomography (micro-CT). Trissolcus euschisi parasitoid development in fresh H. halys eggs fails soon after parasitization either during the egg stage or during early-stage larval development, as limited or no larval development was observed 24 h after initial parasitization. In light of these findings, we propose a time window for further investigation of several potential mechanisms that might result in failed parasitoid development in H. halys.

Different factors (e.g., light, humidity, and temperature) including exposure to static magnetic fields (SMFs), referred here as critical factors, can significantly affect horticultural seed performance. However, the link between magnetic field parameters and other interdependent factors affecting seed viability is unclear. The importance of these critical factors affecting tomato (Solanum lycopersicum L.) var. MST/32 seed performance was assessed after performing several treatments based on a L9 (34) (four factors at three levels) orthogonal array (OA) design. The variable factors in the design were magnetic flux density (R1 = 332.1 ± 37.8 mT; R2 = 108.7 ± 26.9 mT; and R3 = 50.6 ± 10.5 mT), exposure time (1, 2, and 24 h), seed orientation (North polarity, South polarity, and control – no magnetic field), and relative humidity (RH) (7.0, 25.5, and 75.5%). After seed moisture content stabilisation at the different chosen RH, seeds were exposed in dark under laboratory conditions to several treatments based on the OA design before performance evaluation. Treatments not employing magnetic field exposure were used as controls. Results indicate that electrolyte leakage rate was reduced by a factor of 1.62 times during seed imbibition when non-uniform SMFs were employed. Higher germination (∼11.0%) was observed in magnetically-exposed seeds than in non-exposed ones, although seedlings emerging from SMF treatments did not show a consistent increase in biomass accumulation. The respective influence of the four critical factors tested on seed performance was ranked (in decreasing order) as seed orientation to external magnetic fields, magnetic field strength, RH, and exposure time. This study suggests a significant effect of non-uniform SMFs on seed performance with respect to RH, and more pronounced effects are observed during seed imbibition rather than during later developmental stages.

Little is known about the influence of magnetic fields on growth of primitive eukaryotes such as the ciliate Paramecium. The latter are known to exhibit interesting characteristics such as electrotaxis, gravitaxis, and membrane excitability not commonly encountered in higher organisms. This preliminary study reports the effects of static magnetic fields on growth of Paramecium caudatum. The microorganisms were either permanently or 24 h on-and-off exposed to North and South polarity magnetic fields of average field gradient 4.3 T/m, for a period of 96 h. The growth rate and lag phase of all exposed populations were not significantly different from control ones exposed to normal geomagnetic field (P > .05). However, a significant negative shift in tmax (time taken for maximum growth) of 10.5%–12.2% and a significant decrease (P

We studied molecular order in native plant plasma membranes in the presence of static magnetic fields. Plasma membranes of seeds of the tomato plant were purified, extracted, and applied to a silicon substrate in a buffer suspension and their molecular structure was studied using X-ray diffraction. We observed correlation peaks that we assigned to the lipid and protein components of the plasma membrane. Two field strengths were available: B = 0.126 T and B = 0.208 T. While magnetic fields had no observable effect on protein structure, enhanced lipid order was observed, leading to an increase in the gel components and a decrease in the fluid component of the lipids. © 2013 The Royal Society of Chemistry.