Deposition and longevity of oviposition-deterring pheromone in the cabbage seed weevil

Abstract The cabbage seed weevil ( Ceutorhynchus assimilis Payk.) lays eggs singly into pods of oilseed rape ( Brassica napus L.) through punctures bored with the mouthparts, preferring pods not recently used for oviposition. A simple new choice test has been used to test individual components of egg-laying behaviour for their effect on oviposition site selection. It is confirmed that an oviposition-deterring pheromone (ODP) is deposited during abdomen brushing of the pod which follows egg-laying. Neither pin punctures, weevil feeding punctures, oviposition punctures nor eggs had any deterrent effect. Pods walked on by female weevils were not avoided by those laying eggs. Observations suggest that the ODP is sensed by contact chemoreceptors on the antennae. The deterrent effect lasted only 1–2 h. The implications of these findings on the adaptive significance of the pheromone and its possible use in pest control are discussed.     

Scale and uncertainty in modeled soil organic carbon stock changes for US croplands using a process‐based model

Process‐based model analyses are often used to estimate changes in soil organic carbon (SOC), particularly at regional to continental scales. However, uncertainties are rarely evaluated, and so it is difficult to determine how much confidence can be placed in the results. Our objective was to quantify uncertainties across multiple scales in a process‐based model analysis, and provide 95% confidence intervals for the estimates. Specifically, we used the Century ecosystem model to estimate changes in SOC stocks for US croplands during the 1990s, addressing uncertainties in model inputs, structure and scaling of results from point locations to regions and the entire country. Overall, SOC stocks increased in US croplands by 14.6 Tg C yr^?1 from 1990 to 1995 and 17.5 Tg C yr^?1 during 1995 to 2000, and uncertainties were ±22% and ±16% for the two time periods, respectively. Uncertainties were inversely related to spatial scale, with median uncertainties at the regional scale estimated at ±118% and ±114% during the early and latter part of 1990s, and even higher at the site scale with estimates at ±739% and ±674% for the time periods, respectively. This relationship appeared to be driven by the amount of the SOC stock change; changes in stocks that exceeded 200 Gg C yr^?1 represented a threshold where uncertainties were always lower than ±100%. Consequently, the amount of uncertainty in estimates derived from process‐based models will partly depend on the level of SOC accumulation or loss. In general, the majority of uncertainty was associated with model structure in this application, and so attaining higher levels of precision in the estimates will largely depend on improving the model algorithms and parameterization, as well as increasing the number of measurement sites used to evaluate the structural uncertainty.     

Subsidiary-cell development in the Catasetinae (Orchidaceae) and related groups

Developmental studies of stomata in the tribes Cymbidieae, Maxillarieae and Gongoreae (Orchidaceae) demonstrate the presence of definite subsidiary cells in these groups of the Orchidaceae, contrary to recent reports that the Orchidaceae lack subsidiary cells. Fifteen species in these groups were studied developmentally and an additional 36 species were studied from mature leaves. In the Cymbidieae the subsidiary cells may be the lateral trapezoid cells derived from the lateral contact cells, or the subsidiary cells may be derivatives of the trapezoid cells. In the species of Maxillarieae and Gongoreae studied the subsidiary cells were derivatives of the trapezoid cells. The type of subsidiary cell development in these groups is essentially the same as has been found in other advanced groups of epidendroid orchids that have subsidiary cells.     

Antennal contact chemosensilla in Psylliodes chrysocephala responding to cruciferous allelochemicals

Sensilla chaetica, which protrude above all other sensilla on the antenna of Psylliodes chrysocephala L., the cabbage stem flea beetle, were investigated ultrastructurally and found to be innervated by five to six sensory neurones. A dendrite from one of these neurones terminates in a tubular body at the shaft base, whereas dendrites from the others run unbranched to a pore at the shaft tip. Such a structure typifies a sensillum with a combined gustatory/mechanosensory function. Electrophysiological recordings using the tip-recording technique confirmed that this sensillum contains one mechanosensory cell and several chemosensory cells. The chemosensory cells were responsive to host plant chemicals. Sensilla chaetica were also found to be responsive to glucosinolates. One of the sensilla chaetica emerges from a domed area of cuticle on antennomere six. This was found to be relatively less responsive to the chemical stimuli tested and more responsive to mechanical stimulation. It is suggested that the sensilla chaetica are contact chemosensilla, that respond to chemicals present in plant surface waxes when P. chrysocephala antennates a leaf.     

Univariate analysis of tsetse habitat in the common fly belt of Southern Africa using climate and remotely sensed vegetation data

Abstract Tsetse are vectors of trypanosomes that cause diseases both in humans and livestock. Traditional tsetse surveys, using sampling methods such as Epsilon traps and black screen fly rounds, are often logistically difficult, costly and time-consuming. The distribution of tsetse, as revealed by such survey methods, is strongly influenced by environmental conditions, such as climate and vegetation cover, which may be readily mapped using satellite data. These data may be used to make predictions of the probable distribution of tsetse in unsurveyed areas by determining the environmental characteristics of areas of tsetse presence and absence in surveyed areas. The same methods may also be used to characterize differences between tsetse species and subspecies. In this paper we analyse the distribution of Glossina morsitans centralis, Glossina morsitans morsitans and Glossina pallidipes in southern Africa with respect to single environmental variables. For G.m.centralis the best predictions were made using the average NDVI (75% correct predictions; range > 0.37) and the average of the maximum temperature (70% correct predictions; 27.0–29.2°C). For G.m.morsitans the best prediction was given by the maximum of the minimum temperature (84% correct predictions; range > 18.8°C), and for G.pallidipes , also by the maximum of the minimum temperature (86% correct predictions; range > 19.6 °C). The following paper compares a range of multivariate techniques for making predictions about the distribution of these species in the same region.