Summary 1.The shield beetle Cassida rubiginosa Müller (Coleoptera, Chrysomelidae) is one of the most prominent herbivores on creeping thistle, Cirsium arvense (L.) Scop. and is considered as a biological control agent against this weed. In order to investigate if augmented densities of this species could be sustained, predation on C. rubiginosa larvae was studied in the field with the aid of continuous video surveillance of individual prey during three seasons at two different study sites. 2. The paper wasp Polistes dominulus Christ (Hymenoptera, Vespidae) was responsible for 99·4% predation on C. rubiginosa larvae at both study sites. Prey densities were always reduced to a few individuals at the sites after a few days only. Thus, P. dominulus may annihilate the effect of augmentative releases of the beetle as a biocontrol agent. 3. P. dominulus showed no aggregation in patches of high host density (numerical response). The observed density dependence was attributed to the functional response of the wasp. 4. P. dominulus showed a Type III functional response. In mark-and-recapture experiments we found no indication that this type of functional response was the result of single wasps specializing on this particular prey type. 5. Type III functional responses in generalists can result by switching to prey species which become temporarily abundant. Since in a natural setting a mixture of prey species coexists in different abundance and which are differentially accepted by generalist predators, it is imperative to study their functional response in the field.

Summary1. There is a current debate about the appropriateness of prey-dependent vs. ratiodependent functional responses in predator-prey models. This is an important issue as systems governed by these models exhibit quite different dynamical behaviour. However, the issue is not yet resolved on a theoretical basis, and there is a lack of experimental evidence in natural systems. We used a paper wasp-shield beetle system in a natural setting to assess the validity of either approach. 2. We manipulated the abundance of herbivorous insect prey on thistle plants and of predatory paper wasps in the immediate environment of the prey by opening or closing cages containing wasp nests. 3. The number of wasps foraging at the site increased when cages were opened, but rapidly reached an asymptote, indicating predator interference. The predation rate per predator decreased with the number of wasps in the environment. Thus, the functional response depended on both prey and predator density. 4. Neither a pure prey-nor a pure ratio-dependent model fitted perfectly our observations. However, the functional response of the paper wasps towards shield beetle larvae was closer to ratio-dependence. To our knowledge, this is the first experimental evidence discriminating between ratio-and prey-dependence in a natural setting with unconfined predators and prey. 5. Predator interference was most probably responsible for the specific form of the functional response found. We found indications that both direct (e.g. aggression) and indirect interference mechanisms (e.g. depletion of easy-to-find prey) were at work in our system. We conclude that predator density cannot be ignored in models of predatorprey interactions.

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Type 1 diabetes (T1DM) is associated with an increased fracture risk, specifically at nonvertebral sites. The influence of glycemic control and microvascular disease on skeletal health in long-standing T1DM remains largely unknown. We aimed to assess areal (aBMD) and volumetric bone mineral density (vBMD), bone microarchitecture, bone turnover, and estimated bone strength in patients with long-standing T1DM, defined as disease duration ≥25 years. We recruited 59 patients with T1DM (disease duration 37.7 AE 9.0 years; age 59.9 AE 9.9 years.; body mass index [BMI] 25.5 AE 3.7 kg/m 2 ; 5-year median glycated hemoglobin [HbA1c] 7.1% ) and 77 nondiabetic controls. Dual-energy X-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HRpQCT) at the ultradistal radius and tibia, and biochemical markers of bone turnover were assessed. Group comparisons were performed after adjustment for age, gender, and BMI. Patients with T1DM had lower aBMD at the hip (p < 0.001), distal radius (p = 0.01), lumbar spine (p = 0.04), and femoral neck (p = 0.05) as compared to controls. Cross-linked C-telopeptide (CTX), a marker of bone resorption, was significantly lower in T1DM (p = 0.005). At the distal radius there were no significant differences in vBMD and bone microarchitecture between both groups. In contrast, patients with T1DM had lower cortical thickness (estimate [95% confidence interval]: À0.14 [À0.24, À0.05], p < 0.01) and lower cortical vBMD (À28.66 [À54.38, À2.93], p = 0.03) at the ultradistal tibia. Bone strength and bone stiffness at the tibia, determined by homogenized finite element modeling, were significantly reduced in T1DM compared to controls. Both the altered cortical microarchitecture and decreased bone strength and stiffness were dependent on the presence of diabetic peripheral neuropathy. In addition to a reduced aBMD and decreased bone resorption, long-standing, well-controlled T1DM is associated with a cortical bone deficit at the ultradistal tibia with reduced bone strength and stiffness. Diabetic neuropathy was found to be a determinant of cortical bone structure and bone strength at the tibia, potentially contributing to the increased nonvertebral fracture risk.

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Cassida rubiginosa Muell. (Col., Chrysomelidae) is considered to be a native biocontrol agent of the creeping thistle, Cirsium arvense (L.) Scop, one of the world's worst weeds. However, predation is a major mortality factor in C. rubiginosa populations and prevents high beetle densities in nature. We determined temperature-dependent detection periods of shield beetle remains within predators by immunological gut analysis, in order to define the time period within which predation must have occurred. We conducted feeding trials with the model predators Nabis mirmicoides Costa and Chrysopa carnea Stephen at two and three different temperatures, respectively, using C. rubiginosa larvae as prey. Indirect enzyme-linked immunosorbent assay (ELISA) was used to examine the predators for the presence of prey antigen. The monoclonal antibody (MAb) CRL5-1 clearly identified predation by N. mirmicoides for up to 47 h and by C. carnea up to 96 h post-feeding at 15°C. An exponential decay gave a good description of the antigen time course within predators. Calculated detection periods for the antigen were 234.7 h at 15°C and 85.0 h at 20°C in N. mirmicoides and 215.3 h (15°C), 91.9 h (20°C) and 79.1 h (25°C) in C. carnea. The reported detection periods of prey remains in predators are the longest known in immunology, and are much higher than the recently published detection periods of prey DNA in predators. Therefore MAb CRL5-1 is a highly valuable tool for quantifying predation in the field.