Oviposition behaviour as influenced by the oviposition deterring pheromone in the large white butterfly, Pieris brassicae

This thesis deals with a detailed analysis of egglaying behaviour of adult females of the Large White Butterfly, Pieris brassicae, and the way this behaviour is influenced by the oviposition deterring pheromone (ODP) in order to investigate the prospects for field application of this pheromone in cabbage pest control.The study begins with a short introduction on the role of oviposition behaviour in the relationship between herbivorous insects and plants (Chapter 1).In Chapter 2 the ultimate effect of the ODP on egglaying behaviour of Pieris brassicae was demonstrated. In a choice situation with control leaves and ODP treated cabbage leaves females performed a strong preference to lay their eggs on the control leaves. The pheromone, which is associated with the eggs, appeared to be water- and methanol-soluble and could be stored for more than three years without loosing activity. In addition we found some evidence that eggs may contain large amounts of pheromone. The existence of this oviposition deterring pheromone in P. brassicae might contribute to a regular distribution of eggs over available hostplants.In Chapter 3, a detailed description is given of egglaying behaviour of P. brassicae in the absence of the pheromone. This description formed the ethological framework on which further investigations of the behavioural effects of the ODP were based. In addition to this ethogram, the various sensory cues which may be involved in oviposition behaviour are discussed.Perception of the oviposition deterring pheromone by P. brassicae females was studied in some detail in Chapter 4. Electrophysiological experiments indicated that females possess sense cells specifically sensitive to the ODP in their fore-tarsal taste hairs. In morphological studies, by means of the scanning electron microscope, and by electrophysiological recordings we established the presence of contactchemoreceptors on the ovipositor of P. brassicae females. Stimulations with ODP solutions indicated that to some extent these taste hairs might be involved in ODP perception. Responses to hostplant chemicals revealed that hostplant recognition is not mediated by sensory input from these hairs.Chapters 5 and 6 are concerned with an experimental analysis of female preoviposition behaviour in order to determine the detailed behavioural effects of the ODP and the chemoreceptors females actually employ in ODP perception. The experimental set-up was identical in both chapters with single females offered a choice between a control and an ODP treated leaf. The behaviour of females was recorded by means of a keyboard system and afterwards analysed for several parameters, including the sequence of behavioural acts.In Chapter 5 the results with untreated females are described. Our observations indicated that the ODP induces only minor changes in pre- alighting behaviour of these females, suggesting that the pheromone is not very volatile. Most obvious behavioural differences between the two leaves were observed after landing, which indicate that tarsal contactchemoreceptors probably mediate the behavioural response to ODP. In addition, females were observed to perform a reduced tendency to stay on or around the treated leaf. This observation is congruent with the idea that the ODP induces P. brassicae females to disperse.In Chapter 6, these experiments were extended to six groups of females with various sensory ablations. When all six tarsi, whether or not in combination with the antennae, were inactivated (by HCl treatment), oviposition was almost completely suppressed and females did not discriminate anymore between the two types of leaves. In females with intact chemoreceptors on at least one pair of tarsi egglaying activity was about normal and also discrimination was found to occur. Behavioural evidence was presented that females may employ antenna] olfactory hairs, fore-tarsal taste hairs, as well as taste hairs on midand hind-tarsi to perceive the pheromone. Chemoreceptors on the ovipositor were not found to be involved in ODP perception. Finally, it was observed that females did not respond to the ODP anymore once the first egg had been laid.In Chapter 7, the first field tests with the ODP are described. In control experiments without pheromone, the plants chosen for oviposition by P. brassicae females were distributed rather evenly over the cage. When the majority of plants was sprayed with ODP, oviposition attempts were mainly observed on plants along the sides of the cage. This strongly suggests that the ODP indeed evokes females to disperse from the field. The presence of the pheromone did not result, however, in a significant decrease of oviposition on treated plants. This might have been due to our experimental conditions.In Chapter 8, behavioural responses of Pieris rapae butterflies to the ODP of P. brassicae are investigated. ODP treated cabbage leaves remained deterrent to ovipositing P. rapae females for at least 8 days. A conspecific ODP in P. rapae could not be demonstrated. It is concluded that this interspecific effect of the ODP enhances the prospects for field application of this pheromone in cabbage pest control

The effect of gregariousness in cyprid settlement assays

The in vitro settlement assay using cyprids of Balanus, amphitrite is an important tool in basic and applied research. The aim of this study was to quantify the effect of gregariousness within these assays, and to determine the interaction between gregariousness and container size, and settlement promoters and inhibitors. Assays with 1, 5, 10, 15, 20, and 40 cyprids in containers with a log range of surface area to volume ratios were conducted in a fully factorial design. Assays with the same range of cyprid numbers and six concentrations of the settlement promoter 3-isobutyl-1-methylxanthine (IBMX) or the inhibitor phloroglucinol were also conducted in a fully factorial design. Percentage settlement was analysed by GLM ANOVA. Significant (p < 0.05) gregarious effects were detected at ≥ 5 cyprids in a well. Surface area:volume ratio had a strong effect on cyprid settlement, but this effect could be masked by overcrowding in very small wells. Gregarious interactions between only five cyprids magnified the effect of IBMX by a factor of 10, whereas phloroglucinol had no effect without gregarious interactions. The cyprid settlement bioassay is a valuable tool for basic and applied research but must be used with care

The effect of dissolved organic carbon on bacterial adhesion to conditioning films adsorbed on glass from natural seawater collected during different seasons

Adhesion of three marine bacterial strains, i.e. Marinobacter hydrocarbonoclasticus, Psychrobacter sp. and Halomonas pacifica with different cell surface hydrophobicities was measured on glass in a stagnation point flow chamber. Prior to bacterial adhesion, the glass surface was conditioned for 1 h with natural seawater collected at different seasons in order to determine the effect of seawater composition on the conditioning film and bacterial adhesion to it. The presence of a conditioning film was demonstrated by an increase in water contact angle from 15° on bare glass to 50° on the conditioned glass, concurrent with an increase in the amount of adsorbed organic carbon and nitrogen, as measured by X-ray photoelectron spectroscopy. Multiple linear regression analysis on initial deposition rates, with as explanatory variables the temperature, salinity, pH and concentration of dissolved organic carbon (DOC) of the seawater at the time of collection, showed that the concentration of DOC was most strongly associated with the initial deposition rates of the three strains. Initial deposition rates of the two most hydrophilic strains to a conditioning film, increased with the concentration of DOC in the seawater, whereas the initial deposition rate of the most hydrophobic strain decreased with an increasing concentration of DOC

Poly(ethylene glycol)-based thiol-ene hydrogel coatings: curing chemistry, aqueous stability, and potential marine antifouling applications

Photocured thiol-ene hydrogel coatings based on poly(ethylene glycol) (PEG) were investigated for marine antifouling purposes. By varying the PEG length, vinylic end-group, and thiol cross-linker, a library of hydrogel coatings with different structural composition was efficiently accomplished, with or without ester linkages. The thiol-methacrylate and thiol-allyl systems were evaluated with respect to curing, degradation, as well as antifouling properties. Methacrylate-based systems exhibited homopolymerization, whereas allyl-based systems reacted more selectively through thiol-ene couplings reaction. The ester-free hydrogels elucidated higher hydrolytic stability whereas longer PEG chains accelerated the degradation process. The antifouling properties were evaluated by protein adsorption with Bovine serum albumin (BSA) and bioassays with the marine bacteria, Cobetia marina, and the marine diatom, Amphora coffeaeformis; in all tests, longer PEG lengths improved the antifouling propertie

Fluorescence microscopy techniques for quantitative evaluation of organic biocide distribution in antifouling paint coatings: application to model antifouling coatings

A test matrix of antifouling (AF) coatings including pMMA, an erodible binder and a novel trityl copolymer incorporating Cu2O and a furan derivative (FD) natural product, were subjected to pontoon immersion and accelerated rotor tests. Fluorescence and optical microscopy techniques were applied to these coatings for quantification of organic biocide and pigment distribution. Total leaching of the biocide from the novel copolymer binder was observed within 6 months of rotor immersion, compared to 35% from the pMMA coating. In pontoon immersions, 61% of the additive was lost from the pMMA coating, and 53% from the erodible binder. Profiles of FD content in the binders revealed an accelerated loss of additive from the surface of the CDP resulting from rosin degradation, compared to even depletion from pMMA. In all samples, release of the biocide was inhibited beyond the Cu2O front, corresponding to the leached layer in samples where Cu2O release occurred