Ecological genetics of Melaleuca quinquenervia (Myrtaceae): Population variation in Florida and its influence on performance of the biological control agent Oxyops vitiosa (Coleoptera: Curculionidae)

Melaleuca quinquenervia (Cav.) Blake (Myrtaceae) was imported into Florida from Australia over a century ago as a landscape plant. A favorable climate and periodic wildfires helped M. quinquenervia thrive; it now occupies about 200,000 hectares in southern Florida. A biological control (i.e., biocontrol) program against M. quinquenervia has been initiated, but not all biocontrol releases are successful. Some scientists have argued that poor biocontrol agent success may relate to genetic differences among populations of invasive weeds. I tested this premise by determining (1) the number and origins of M. quinquenervia introductions into Florida, (2) whether multiple introduction events resulted in the partitioning of Florida's M. quinquenervia populations into discrete biotypes, and (3) whether Oxyops vitiosa, an Australia snout beetle imported to control this weed, might discriminate among putative M. quinquenervia biotypes. Careful scrutiny of early horticultural catalogs and USDA plant introduction records suggested at least six distinct introduction events. Allozyme analyses indicated that the pattern of these introductions, and the subsequent redistribution of progeny, has resulted in geographic structuring of the populations in southern Florida. For example, trees on Florida's Gulf Coast had a greater effective number of alleles and exhibited greater heterozygosity than trees on the Atlantic Coast. Essential oil yields from M. quinquenervia leaves followed a similar trend; Gulf Coast trees yielded nearly twice as much oil as Atlantic Coast trees when both were grown in a common garden. These differences were partially explained by the predominance of a chemical phenotype (chemotype) very rich in the sesquiterpene (E)-nerolidol in M. quinquenervia trees from the Gulf Coast, but rich in a mixture of the monoterpene 1,8-cineole and the sesquiterpene viridiflorol in trees from the Atlantic Coast. Performance of O. vitiosa differed dramatically in laboratory studies depending on the chemotype of the foliage they were fed. Larval survivorship was four-fold greater on the (E)-nerolidol chemotype. Growth was also greater, with adult O. vitiosa gaining nearly 50% more biomass on the (E)-nerolidol plants than on the second chemotype. The results of this study thus confirmed the premise that plant genotype can affect the population dynamics of insects released as weed biocontrols. ^

Sugar and coffee: A history of settler agriculture in nineteenth-century Liberia

This dissertation is about commercial agriculture in nineteenth-century Liberia. Based primarily on the archives of the American Colonization Society (founder of Liberia), it examines the impact of environmental and demographic constraints on an agrarian settler society from 1822 to the 1890s. Contrary to the standard interpretation, which linked the poor state of commercial agriculture to the settlers' disdain for cultivation, this dissertation argues that the scarcity of labor and capital impeded the growth of commercial agriculture. The causes of the scarcity were high mortality, low immigration and the poverty of the American “Negroes” who began to settle Liberia in 1822. ^ Emigration to Liberia meant almost certain death and affliction for many immigrants because they encountered a new set of diseases. Mortality was particularly high during the early decades of colonization. From 1822 to 1843, about 48 percent of all immigrants died of various causes, usually within their first year. The bulk of the deaths is attributed to malaria. There was no natural increase in the population for this early period and because American “Negroes” were unenthusiastic about relocation to Liberia, immigration remained sparse throughout the century. Low immigration, combined with the high death rate, deprived the fledgling colony of its potential human resource, especially for the cultivation of labor-intensive crops, like sugar cane and coffee. Moreover, even though females constituted approximately half of the settlers, they seldom performed agricultural labor. ^ The problem of labor was compounded by the scarcity of draft animals. Liberia is in the region where trypanosomiasis occurs. The disease is fatal to large livestock. Therefore, animal-drawn plows, common in the United States, were never successfully transplanted in Liberia. Besides, the dearth of livestock obstructed the development of the sugar industry since many planters depended on oxen-powered mills because they could not afford to buy the more expensive steam engine mills. ^ Finally, nearly half of the immigrants were newly emancipated slaves. Usually these former bondsmen arrived in Liberia penniless. Consequently, they lacked the capital to invest in large-scale plantations. The other categories of immigrants (e.g., those who purchased their freedom), were hardly better off than the emancipated slaves. ^