No description available.

No description available.

No description available.

Approximately 5,000 years ago, eastern hemlock ( Tsuga canadensis) experienced a sudden, rapid, range-wide decline most probably due to pest, disease, or climate change. An aphid-like defoliating insect, the hemlock woolly adelgid (Adelges tsugae), recently (1950’s) introduced to eastern North America has been spreading across the eastern United States. The adelgid attacks all size and age classes of hemlocks causing up to 95% mortality in affected stands. The potential for another range-wide hemlock decline has raised a number of concerns including the increased threat of wildfire. Altered fuel loadings in modern adelgid-affected stands and the effects of presumably similar changes in fuels and subsequently altered fire regimes following the prehistoric decline are examined. Fuels data from an adelgid-infested stand in Connecticut and an uninfested stand in Massachusetts were used to generate custom fuel models and predict fire behavior in each stand. Sediment cores were extracted from three sites in western Massachusetts and analyzed for fossil pollen and charcoal around the period of the prehistoric decline. Fossil data from two previously studied sediment cores from coastal Maine are included in the analysis. Results demonstrate a clear and highly significant increase in both fuel loadings and predicted fire behavior in the modern, adelgid-affected stand. Three of the coring sites reflect distinct, significant, short-lived increases in charcoal associated with the prehistoric decline; two do not. Results from the first three sites suggesting increased fire activity also were associated with changes in vegetation which indicate disturbance. Increased fire activity after the decline seems most pronounced in areas where fire was common before the decline. Results indicate that fire was not universally a significant factor driving post-decline succession. Research across a broader geographic area is needed to clarify the relationship between fire and hemlock following the mid-Holocene decline, but the results presented here suggest that managers of modern stands affected by the adelgid should include the possibility of intense fires as a threat to landscapes heavily affected by hemlock decline.

The ambermarked birch leafminer (AMBLM) (Profenusa thomsoni) is an invasive leafminer native to the Palearctic from the United Kingdom to Turkey to Japan. It was introduced to the eastern United States in 1921 and has since spread to the mid-western U.S. states and Canadian provinces. This leafminer was introduced to Alaska in 1996, where it has since spread over 140,000 acres, from Haines to Fairbanks. The most severe damage is found throughout the Anchorage bowl, which extends south to Girdwood and North to Wasilla. The damage caused by P. thomsoni can be severe, defoliating entire trees. In 2006, it was noted that urban areas in Alaska experienced higher densities of AMBLM leafminer than adjacent forested areas. To examine the effects of habitat on leafminer densities, twenty permanent plots were established in Anchorage, Alaska in 2006 and were classified as urban and forest (ten each). Temperature records for the twenty permanent sites showed that average daily temperatures and average accumulated degree-days differed significantly between urban and forest sites. In 2007 and 2008, leafminer abundance in each habitat was examined weekly at six plots (three urban and three forest) within the city of Anchorage. Asynchronous emergence, flight, and oviposition times were observed between leafminers in forests versus urban areas, with peaks of these parameters in forests being about three weeks later than in urban areas. To control the spread and effects of P. thomsoni, a cooperative biological control project was launched in 2003 and the parasitoid wasp Lathrolestes thomsoni (Hymenoptera: Tenthredinidae) was selected for release. Parasitized leafminer larvae were collected from the provinces of Northwest Territories and Alberta, in Canada and transferred in soil tubs as pre-pupae to Alaska. From 2004-2008, 3636 adult L. thomsoni adults were released in birch tree stands in Anchorage, Soldotna, and Fairbanks, Alaska. Parasitoids have been recovered at all release sites in Alaska and have established populations at most release sites. Currently, AMBLM densities have declined by over 40% in the Anchorage area and the spread of the leafminer throughout the state appears to have slowed. Throughout the course of the biological control program two additional parasitoids were discovered attacking P. thomsoni in Alaska. The first, Lathrolestes soperi, an endoparasitoid with similar biology to the released parasitoid L. thomsoni, was found to attack early instar larvae within the leaf. The second species, Aptesis segnis, is an ecotoparasitoid that attacks pupae and prepupae in their earthen cells in soil. Lathrolestes soperi was found to contribute a significant proportion of mortality against the leafminer. The presence of A. segnis in the parasitoid guild raised mortality of P. thomsoni to 40.3%, showing that the percent parasitism by A. segnis was 26%, double that provided by L. soperi. This suggests that A. segnis is the dominant parasitoid in the guild. It is unknown what effect that the introduced wasp L. thomsoni will have on the presumably native L. soperi and if one species will outcompete the other over time, or both will coexist. Future work on this system is recommended in five to ten years to see if L. thomsoni and L. soperi populations remain stable or to see if one parasitoid outcompetes the other and if A. segnis maintains its dominant place in the system.

Cockroach fat body vitellogenesis has been employed as a model for studies concerning the juvenile hormone (JH) induction and biosynthetic processing of insect vitellogenins (VGs). Fat body of Blaberus discoidalis was shown to synthesize and secrete two discrete VGs in response to JH. Oocyte-bound vitellins (VTs) corresponding to each VG were purified by salt fractionation and gel filtration. The native VTs were of similar size (17S, 8.8 nm radii, 680K Mr), yet (i) separated in NaBr density gradients, (ii) possessed unique peptide substructures (6 and 8 peptides of 36K to 192K Mr), and (iii) were immunologically unrelated. Using antiserum to purified VT, precursor VGs for each VT were demonstrated to be synthesized and secreted by fat body cultured in vitro. In fat body cytosol, JH binding components potentially mediating JH induction of VG were indicated by a developmental concomitancy in the onset of vitellogenesis, and the expression of a saturable, specific, high-affinity JH-III binding protein (Kd (TURN) 10-9M, 5.5nm radius, 7.5S, 180K Mr). Prior to equilibrium analyses, JH-degradative, low Mr fat body esterases were separated from JH binding activity on Biogel A-1.5. The JH analogue ZR-515 competed for saturable JH-III sites (Kd (TURN) 2 x 10-6) while farnesal did not, indicating that both the epoxy and terminal ester functions of JH were required for efficient binding. Additionally, maximum likelihood nonlinear regression analysis of equilibrium data, JH-III dissociation kinetics, and DEAE-Cellulose fractionation of JH binding activity resolved a second JH binder (Kd (TURN) 10-8 M) constitutively expressed by fat body. In Blattella germanica, efficient in vivo radiolabeling of VG allowed an examination of the role of glycosylation in its biosynthetic processing and secretion from fat body. The antibiotic tunicamycin inhibited VG glycosylation and the subsequent cleavage of a pro-VG peptide into the 160K and 100K peptides of controls. Glycosylation was also required for the efficient secretion of VG from fat body. Mapping of VG and VT peptides helped to define the normal sequence of VG processing during its secretion and ovarian storage.

Includes bibliographical references (leaves 94-107). / The Australian river red gum (Eucalyptus camaldulensis Denhardt) (Myrtaceae) is regarded in South Africa as a valuable general-purpose utility and ornamental tree, as well as an essential source of nectar and pollen to sustain the honeybees which are crucial for pollinating the economically important fruit crops in mainly the Western Cape Province. Despite its utility value, it is regarded as invasive in South Africa, the major concern being the large amounts of water it consumes when growing along watercourses. River red gum is therefore the subject of conflicts in interests between government agencies that target it for control actions, and farmers and beekeepers who utilize it. As a contribution towards resolving this conflict in interests, a research project was initiated to investigate the potential use of host-specific insects that might reduce the number of viable seeds produced by E camaldulensis. The aim was to reduce its invasive potential while retaining its general utilizability for all concerned. From the start, the need for introduced agents from Australia was weighed against the presence of two species of chalcidoid wasps, both regarded as gall inducers, in the seed capsules of E camaldulensis in South Africa. The current study was motivated by the need for information on the biology of these two species and the effect they were having on seed production in their host plant. As it progressed, three more chalcidoid species, all undescribed at that time and probably of Australian origin, were found to be emerging from the seed capsules of E camaldulensis collected in several parts of South Africa, and these became part of the investigation.

<p> </p> <p>The relationship between termites and their gut microbiome is inseparable as the microbes provide plenty of physiological benefits such as digestion, acetogenesis, nitrogen fixation, caste differentiation and immunity. Therefore, it is very important to understand this relationship to attain innovations in pest management solutions. This project was undertaken to study the dynamics of termite gut microbiomes in response to environmental and colony-genetic factors. Here I investigated environmental variations under lab conditions by manipulating the social environment of termite workers via hormonal treatments (Chapter 2) and by exposing termites to commonly used insecticides (Appendix A). To investigate the interaction of gut microbes with natural environmental variation, I sampled field termites every month from May through October (Chapter 3). In addition, to study the impact of termite colony genetics, I reared termites originally from two different field colonies in a controlled environment in the lab (Chapter 4). The combination of lab and field investigations, and bioinformatic analyses have resulted in the following major findings- (1) gut microbes do impact the social environment within a colony, (2) seasonality has an impact on gut microbial abundances, (3) significant variation in microbiome follows genetics of termite colonies, and (4) insecticide applications do change the gut microbial loads specifically the protists load.</p> <p>Results from these experiments support the idea that termite gut symbionts change their community structure possibly to help the host termite to be best fit to survive changing environmental conditions. For example, when termites were provided hormonal treatment to artificially induce caste differentiation, gut microbes were linked with this eusocial mechanism via differential selection. However, when termites were in the field experiencing change in the season, monthly temperature was correlated with several bacterial taxa, possibly selecting for taxa that help termite to thrive the changed environmental conditions. These results indicate that studying termite system without considering their gut microbiome would not provide a complete picture of physiological, biological or pest management studies. This dissertation altogether highlights the possible dynamics of gut microbiome to help a host adapt to changing conditions and emphasizes the importance of a holobiont approach while studying an insect system. </p>

Citrus fruits are one of the world’s major fruit crops, ranking first in trade value among all fruits and significantly contributing to global food and nutritional security. In Africa, South Africa is the leading producer of citrus with an annual production of 2.4 million tons whereas the leading producers in East Africa are: the United Republic of Tanzania and Kenya with an annual output of about 500,000 and 190,000 tons, respectively in 2017. The reason for this low production is attributed to the incidence of the African citrus triozid (ACT), Trioza erytreae Del Guercio (Hemiptera: Triozidae) and other pests and diseases. In Kenya, T. erytreae is considered the most important pest only after aphids, Toxoptera citricidus Kirklady. Though T. erytreae causes death of young shoots, it is considered economically important because it vectors “Candidatus” Liberibacter africanus (CLaf), causative bacteria of the citrus greening disease (CGD). Citrus greening disease and its Asian counterpart, Huanglongbing (HLB) vectored by the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) are the most economically important diseases of citrus worldwide. Since the greening disease has no known cure, management is mainly aimed at the vector. Using behavioural assays and chemical analysis, the interaction between T. erytreae and Citrus jambhiri Lush. (Sapindales: Rutaceae), a common host plant was studied. Nine- and three- component blends comprising limonene, sabinene and β-ocimene, the most abundant terpenes in rough lemon volatiles, were identified from the healthy host plant as a potential arrestment/short-range host location cue for T. erytreae. However, a six-component blend lacking in these three components elicited an avoidance response in both sexes. Trioza erytreae-infested host plants were unattractive to T. erytreae. On the other hand, Tamarixia dryi Waterston (Hymenoptera: Eulophidae), the nymphal parasitoid of T. erytreae was attracted to both uninfested and infested host plants, when they were presented simultaneously with plain air. However, when presented with uninfested and infested host plants simultaneously, it preferred the latter. Chemical analysis of T. erytreae-infested plants revealed the induction of Methyl N-methylanthranilate (MNMA) and methyl anthranilate (MeA). Thus, these compounds could be responsible for the observed avoidance by T. erytreae, suggesting, that citrus plant is able to defend itself against herbivory. (E)-β-Caryophyllene was upregulated in CLaf-infected plants and it was shown to increase attraction of T. erytreae to the infected plants. Additionally, methyl salicylate (MeSA), (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), p-ethyl acetophenone and geranyl acetone, among other compounds were induced in the diseased plants. The effect of non-host plants volatiles, lemongrass (Cymbopogon citratus (DC) Stapf (Poales: Poaceae)), garlic (Allium sativum L. (Asparagales: Amaryllidaceae)) and guava (Psidium guajava L. (Myrtales: Myrtaceae)) were screened against T. erytreae responses using a newly developed cage assay. Results showed that garlic and guava but not lemongrass odours, possessed repellent effect against triozids, thus can be potential border plants which can be used to manage T. erytreae in citrus nurseries or orchards. These findings help to better understand the chemical ecology of the triozid and its interspecific relationships with host and non-host plants. Identified kairomones and repellent crops can be useful in a push-pull strategy against the pest. / Thesis (PhD (Entomology))--University of Pretoria, 2020. / BMZ/ GIZ through the project on “Strengthening Citrus Production Systems through the Introduction of Integrated Pest Management (IPM) Measures for Pests and Diseases in Kenya and Tanzania (SCIPM)” (Project no.: 14.1432.5-001.00/Contract no.: SCIPM 81180346) through the International Centre of Insect Physiology and Ecology (icipe); UK Aid from the UK Government; Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); and the Kenyan Government. AKAA was supported by a German Academic Exchange Service (DAAD) In-Region Postgraduate Scholarship. / Zoology and Entomology / PhD (Entomology) / Restricted

Tsetse flies (Diptera: Glossinidae) are vectors of the trypanosome parasites causing African trypanosomosis which hinders sustainable agriculture and livestock production, affects human health, and negatively impacts the economy of most African countries. Available vector control strategies including sequential aerosol techniques, use of stationary attractive devices and live baits, and sterile insect techniques have limitations and are mostly used in tandem. Sense of smell largely dictates tsetse flies’ ability to discriminate among preferred hosts such as buffalo and cattle, and non-preferred ones including waterbuck and zebra, and can be exploited for innovative vector control strategies. Previous studies identified a four-component repellent blend, waterbuck repellent compounds (WRC), comprising geranyl acetone, guaiacol, pentanoic acid and δ-octalactone, from waterbuck, a non-preferred host. Among the equids, zebra is less preferred by tsetse flies for blood feeding compared to horse and donkey. However, the chemical basis for this feeding preference has not been elucidated, thus the focus of this study. Chapter one is a general introduction of the study. Chapter two investigated the semiochemical basis of the avoidance of zebras by tsetse flies. Crude skin odours of zebra were evaluated for repellency on savannah tsetse flies Glossina pallidipes in the field. Odour extracts were subjected to chemical analyses (gas chromatography-mass spectrometry, GC/MS and GC-electroantennographic detection, GC/EAD) to identify physiologically-active compounds. Identified compounds were screened for repellency in field-based behavioural assays. It was established that zebra skin volatiles contribute to the avoidance behaviour of the savannah tsetse fly, G. pallidipes. Tsetse flies consistently detected and responded to three ketones (6-methyl-5-hepten-2-one, acetophenone, geranyl acetone) and four aldehydes (heptanal, octanal, nonanal, decanal) from zebra skin odours. Additionally, a synthetic blend of the three ketones (blend K) repelled G. pallidipes in a similar way as the known tsetse repellent blend, WRC. In chapter three, the three repellent compounds identified from zebra skin in chapter two were evaluated for repellency on the riverine tsetse fly G. fuscipes fuscipes, whose chemical ecology has mostly been understudied but are key vectors of trypanosomes causing HAT. The three-component blend (blend K) significantly reduced field trap catches of G. f. fuscipes, similar to WRC. Geranyl acetone, a component of both WRC and blend K, exhibited comparable repellency to the blends (WRC and blend K). Chapter four presents a comparative analysis of GC/MS skin volatile profiles of zebra and two other equids (donkey and horse). Results show skin odours of the three equids contain the seven EAD-active compounds earlier identified in Chapter two. Moreover, there were quantitative variations of these compounds among the equids, with generally higher concentrations in zebra odours in relation to donkey and horse. Taken together, the study established the allomonal effect of zebra skin on both savannah and riverine tsetse flies and revealed the semiochemical basis for the differential attraction of tsetse flies to the equids examined. The three-component repellent blend identified in zebra skin odour has potential for integration into the management toolkit for savannah and riverine species of tsetse flies and African trypanosomosis. / Thesis (PhD (Entomology))--University of Pretoria, 2020. / Zoology and Entomology / PhD (Entomology) / Unrestricted