A number of organochlorine insecticides have been examined for both their in vitro and in vivo effects on the biphenyl system for detecting potential carcinogens. This test is based on previous findings that biphenyl 2-hydroxylase can be selectively enhanced by carcinogens. DDT, DDE, DDD and aldrin caused a statistically significant in vitro stimulation of biphenyl 2-hydroxylation after an initial preincubation period with liver microsomes. Dieldrin, however, elicited such a change without any preincubation. These increases were difficult to interpret since it was shown that at least part of the apparent stimulation produced by known carcinogens such as safrole, 3-methylcholanthrene and 3,4-benzpyrene, was due to the generation of fluorescent metabolites that interferred with the determination of 2-hydroxybiphenyl formation in the assay used. Single intraperitoneal administration of test chemicals to rats showed that the carcinogen, 3-methylcholanthrene, caused a selective enhancement of biphenyl 2-hydroxylase activity whereas phenobarbitone affected both the 2- and 4-hydroxylases to a similar extent. However, induction patterns observed for compounds such as alpha-benzene hexachloride, which is carcinogenic, or delta-benzene hexachloride, which is noncarcinogenic to rats, showed no differences. A long-term feeding study was carried out in rats with dietary DDT at 250 ppm and 500 ppm. Histological, histochemical and ultrastructural alterations in the liver were compared with sequential measurements of hepatic drug-metabolizing enzyme activity. Induction of these enzymes was observed within 10 days of feeding, and this was sustained throughout the experimental period. There was no evidence of liver injury in animals of either dose group up to the termination of treatment at 8 months.

Laboratory-based behavioural bioassays were used to examine the locomotor activity and feeding behaviour of <i>C.</i> <i>septempunctata </i>in response to residues and odours of five commercial insecticides, whose active ingredients were chlorpyrifos (an OP), cypermethrin (a pyrethroid), l-cyhalothrin (a pyrethroid), dimethoate (an OP), and pirimicarb (a carbamate). The greatest behavioural changes were observed in response to the pyrethroids, which reduced locomotor activity, but did not significantly affect mortality. The OPs also affected locomotor behaviour, albeit to a much smaller degree, and significantly increased mortality. The carbamate did not lead to changes in any of the variables tested throughout the study. The same patterns were observed regardless of application rate or spray pattern. Only limited responses were observed to the active ingredients of the products. Pyrethroid-contaminated prey significantly reduced feeding levels, but did not kill the predators. OP-contaminated prey altered feeding rates to a lesser extent, but caused significant levels of mortality. <i>C. septempunctata </i>did not respond behaviourally to odours of the test compounds. Scanning electron microscopy revealed that the greatest numbers of chemically responsive sensilla were located on the maxillary palps, and electrophysiological examination confirmed their sensitivity to both the dimethoate-based product and to the carrier formulation. This may act to reduce insecticide exposure in the field, and preserve the coccinellids in crop strata receiving lower doses, allowing greater aphid control in the days following insecticide application. The mechanism for detection involves contact chemoreception of the carrier formulation, and not olfaction. The use of pyrethroid-based insecticides in IPM requires further study to determine the full impact and potential of these chemicals.

No description available.

Spiders (Arachnida: Araneae) are important polyphagous predators which limit pest numbers in arable crops. To utilise them fully as part of an IPM (integrated pest management) programme a greater understanding of basic population dynamics and ecology is required. Two species common to UK arable land: <I>Lepthyphantes tenuis</I> (Blackwall) and <I>Enoplognatha ovata</I> (Clerck) were studied. These species exhibit different rates of dispersal; the former a highly dispersive ballooning spider, the latter a more sedentary species - permitting the effect of dispersal on patterns of genetic variation to be examined. RAPD data were generated via 5 decamer primers and used to determine variation between and within populations at a local scale (<100 km). Individuals within a species showed a high degree of similarity calculated via the Nei and Li similarity coefficient (<I>E. ovata</I> >83% and <I>L. tenuis</I> >54%). Despite this high level of similarity, PCO (Principle Co-Ordinate) analysis detected a pattern within the similarity matrix which could be related to the geographical separation of the populations. A less obvious structure was detected by PCO analysis of <I>L. tenuis</I> samples. Further statistical analysis revealed that F<SUB>st</SUB> estimates were higher, and heterozygosity levels lower, within <I>E. ovata</I> populations than <I>L. tenuis</I> populations emphasising the effect of dispersal and gene flow on reducing population structure. PCR-RFLP of a rDNA fragment containing ITS1 and 2 was carried out as an initial screen of variability with populations of <I>L. tenuis</I> from England, Scotland and New Zealand, and <I>E. ovata</I> populations from Dundee, Edinburgh and Elgin. Near identical RFLP patterns were found within a species. To investigate variation at the finest level, multiple ITS1 clones from one individual from each site were sequenced in both species. A total sequence variation of 2.7% was recorded across 10 <I>E. ovata</I> clones and 1.5% across 10 <I>L. tenuis</I> clones.

Phytophagous insects such as lepidopteran species utilise both olfactory and visual cues to locate their host-plants used as mating or oviposition sites, shelter or food. Larvae of <i>Acraea acerata </i>feed on sweet potato plant leaves causing more that 50% loss of sweet potato tuber yield in some East African countries. Attempting to elaborate a management strategy to control <i>A. acerata </i>suitable to a tropical resource-poor farming system, it was essential to investigate how the butterfly finds its hosts-plants. The results of a wind tunnel bioassay using glass-screened, muslin-screened and non-screened sweet potato plants suggested that sweet potato plant volatiles play an important role in attracting <i>A. acerata </i>to its host-plant. This was supported by both the distance moved by female <i>A. acerata </i>towards muslin-screened plants (olfactory cues) and the percentage of butterflies which landed on the screen. Visual stimuli seemed to have a negative effect. The attractiveness of sweet potato plant volatiles to <i>A. acerata</i> was later confirmed by the use of volatiles collected by headspace entrainment from sweet potato plants. The main components of sweet potato plant volatiles were tentatively identified by GC-MS (Gas Chromatography coupled with Spectrometry) analysis and electrophysiological responses were recorded for some of them. Compared to ethylbenzene, 3-carene and (-) trans-caryophyllene, 3-hexen-1-ol,(Z), a general green leaf alcohol, elicited far more substantial EAG (electroantennogram) responses in <i>A. acerata.</i> This result suggested that <i>A. acerata</i> might well respond to a specific blend of volatiles made up of the different chemical components of sweet potato plant volatiles instead of one or two specific chemical components. Considering the important role of sweet potato plant volatiles in attracting <i>A. acerata, </i>a number of plants reported to be repellent to herbivorous insects were mixed with sweet potato plants and screened for repelling/disorienting of female <i>A. acerata</i> in olfactometer and wind tunnel bioassays.

The use of space by laying hens in free-range systems is often very uneven, with birds displaying an apparent reluctance to leave (and move away from) the house. Using mainly small groups as models for the larger flocks normally housed in commercial free-range systems, this thesis investigated the role of social and environmental factors on hens' movement and use of space. Hens displayed a greater readiness to emerge from a familiar covered box into an unfamiliar outdoor area when the outdoor area contained familiar feeders, even though the birds had free access to food in their home pens. Emergence latencies decreased with repeated testing. Birds also spent more time in the outdoor area when feeders were present, though they tended not to move past the feeder which was nearest the box. Birds which had been exposed to an enriching stimulus (traffic cones) in their home pens tended to leave the box earlier than those which had not, thought this was not dependent on the actual presence of cones in the outdoor area. This suggests that a more complex home environment can influence birds' responses to novel environments. Furthermore, the order of emergence into the paddock was not significantly influenced by social rank. Birds which had been regularly exposed to the outside environment during the rearing process displayed little or no fear of the outdoor area as adults. In contrast, regular handling had little effect on birds' readiness to enter the outdoor area. Regular exposure to the outside environment also reduced birds' underlying fearfulness (measured by tonic immobility), both in small experimental groups and in a larger free-range flock.

The electrophysiological and behavioural responses of the aphidophagous hoverfly <I>Episyrphus balteatus</I> Degear, and polyphagous ground beetles <I>Pterostichus melanarius</I> Illiger and <I>Nebria brevicollis</I> Linneaus, to a range of volatile semiochemicals were studied. <I>Phacelia tanaectfiolia </I>flower extract, <I>Nepeta cataria </I>whole plant extract, and (E)-β-farnesene where found to be attractive to the predators in laboratory and windtunnell assays. Field trials demonstrated that the attractive semiochemicals could be placed in dispensers in arable crops to increase the amount of predators present throughout the field system. There was also a corresponding decrease in the number of pest species present in the treated field plots relative to the control plots. <I>Phacelia </I>flower extract was found to have the greatest effects on predator and prey numbers. The mechanisms of the reduction in prey numbers were studied using exclusion experiments in the field and enzyme linked immunosorbant assays on the gut contents of the predators. There was found to be a link between the increased rates of predation in the field and the decline in pest numbers. The potential of semiochemicals to enhance natural control of crop pests is discussed.

Beds are a crucial source of house dust mite (HDM) allergens, which play a major role in allergic disease, particularly asthma. HDM require a specific combination of hygrothermal conditions to thrive. These bed conditions depend on a number of interacting factors, such as: external climate; building characteristics; heating, ventilation and moisture-producing habits; mattress properties; etc. Because of the complexity of the many interacting factors occuring in real dwellings, a modelling approach is required, whereby the models' predictions have to be consistent with field results. This thesis tested the hypothesis that a combined HDM population-hygrothermal model for beds can adequately predict field data and that the model can be a valuable tool for scenario modelling and intervention studies focused on the psychrometric control of house dust mites in UK housing. Two combined models were considered: a simple steady-state one-dimensional model (BED/MPI), and a complex transient three-dimensional mode (Lectus/Popmite). A combination of fieldwork and scenarios modelling was carried out, which involved hygrothermal and mite monitoring of 25 beds, utilising a novel technique whereby live mites were caged in mite bags and installed in monitored beds and bedrooms (82 sets of mites bags). The work was carried out as part of a multidisciplinary project aimed at developing and testing the models. Good agreement was found between field data and the models predictions, particularly when the uncertainties due to input variables and measurements were taken into account. The results showed that under borderline conditions for HDM growth, simple steady-state predictions may not be accurate. Temperature, not only RH, is a critical variable for HDMs. Areas for model improvement were also identified. In particular, factors other than hygrothermal conditions may be crucial for a beds mite carrying capacity, requiring further investigation: food, space availability, and mite movement. Despite these uncertainties, it can be concluded that greater ventilation, increased thermostat settings and reduced moisture rates can decrease mite levels in beds. The ventilation rates provided by some mechanical ventilation with heat recovery systems may be inadequate to sufficiently control moisture and reduce mite growth. Scenarios modelling suggests that there is considerable potential for the psychrometric control of house dust mites in UK dwellings.

Microbial symbionts of insects have been demonstrated to play an important role in the nutrition and protection of the host; these include aphids and tsetse. Studies often use antibiotics to eliminate the symbionts but the deleterious impact of using these antibiotics is not commonly addressed. The impact of chlortetracycline treatment on Aedes aegypti and Drosophila melanogaster was investigated by assessing life-span, fecundity, development time, survival, nutrition and metabolism. The impact on microbial numbers and diversity was also determined. With Drosophila, treatment with 50 µg ml-1 and above showed a significant extension in development time and life-span, reduction in fecundity and change in nutritional content. Microbial numbers were significantly reduced at 50 µg ml-1 and above. Culturable techniques and 454 pyrosequencing, demonstrated that the microbial diversity of Drosophila was predominantly Acetobacter. Bacterial elimination through egg dechorionation yielded some similar results to chlortetracycline treatment. However, fecundity and life-span was not significantly affected. Microarray analysis established a significant reduction in the abundance of transcripts associated with immunity, particularly antimicrobial peptides. With Aedes aegypti, treatment significantly reduced the survival and also affected the life-span and nutrition of the insect. Microbial numbers of mosquito larvae were reduced at 30 and 100 µg ml-1. Colonies grew on plates supplemented with 50 µg ml-1 of chlortetracycline, indicating that the larvae bore chlortetracycline-resistant bacteria. 454 pyrosequencing demonstrated a change in diversity of bacteria found in mosquitoes +/- chlortetracycline, switching from Elizabethkingia meningoseptica to Raoultella sp with chlortetracycline. It is concluded that chlortetracycline significantly impacts the performance of the 2 insects through bacterial depletion, changes to bacterial diversity and toxicity. Nevertheless, different responses were observed with Aedes aegypti and Drosophila melanogaster. Moreover, experiments with Drosophila using egg dechorionation, emphasised the toxic impact of using antibiotics to eliminate microbes in the insect host.

During the last few year dengue has become an emerging vector borne disease in Pakistan. Aedes aegypti once considered eradicated from almost whole of Pakistan was again collected from 13 different cities. This mosquito has not only started reinvading its previously occupied areas (Karachi, Peshawar and Lahore) but is also spreading to new areas where it was not present before (Attock, Haripur, Hasanabdal, Taxilla, Rawalpindi, Gujranwala, Sheikhupura, Faisalabad, Multan and Hyderabad). This mosquito is breeding in almost all types of artificial containers especially in tyres. Though this mosquito is mostly using outdoors containers for ovipositon but was also found breeding indoors in household. Eleven microsatellite markers were used to determine the genetic population structure of Aedes aegypti in Pakistan using mosquitoes collected from 13 different cities. There appears to be a single population of this mosquito in Pakistan with a pattern of isolation by distance rather than distinct sub-populations. The large scale of isolation by distance suggests long range passive dispersal which may be facilitated by the tyre trade in Pakistan. A decrease in genetic diversity from north to south suggests a recent spread of this mosquito from Karachi. A strong negative correlation between genetic distance and quality of road connections between cities suggests human-aided passive dispersal of Ae. aegypti in Pakistan. Dengue detection in mosquitoes collected from different areas of Pakistan with special reference to tyres shows that vertical transmission is not playing any significant role in the maintenance of dengue virus in mosquito of population. Absence of virus in larvae collected from tyres suggest that though tyres are playing important role in the spread of vector mosquito in Pakistan but its not playing any role in the spread of dengue virus in the study area. The long-range dispersal of Aedes aegypti in Pakistan could facilitate the strategy of introducing transgenic Aedes aegypti or an intracellular bacterium, like the endosymbiotic Wolbachia, for controlling the population of this dengue vector in Pakistan.