The performance and preference of a specialist herbivore, Catorhintha schaffneri (Coreidae), on its polytypic host plant, Pereskia aculeata (Cactaceae)

Plant species moved beyond their natural ranges may be liberated into enemy-free spaces, where they increase resource allocation to fitness, rather than defence against natural enemies, and become invasive as suggested by the Evolution of Increased Competitive Ability (EICA) Hypothesis. Several cacti are notable invaders and are targeted for biological control. The leafy cactus, Pereskia aculeata Miller, introduced into South Africa from South America, has become a target for biological control after becoming invasive. The absence of natural enemies of P. aculeata in the introduced range may be the reason for its invasiveness. This thesis seeks to investigate the role of the evolution of increased competitive ability (enemy release) as the probable driver of P. aculeata’s success, and ascertain how the plant’s intraspecific variation influences the impact, fitness of, and preference by its biological control agent, Catorhintha schaffneri Brailovsky and Garcia (Coreidae), in South Africa. Enemy release and evolution of traits in P. aculeata were examined by quantifying plant growth parameters of fifteen genotypes of P. aculeata from both the native and invaded distribution of the plant. Ten genotypes of P. aculeata were used in testing the effect of agent herbivory (impact and damage) under similar conditions. These studies indicated that most invaded-range genotypes were more vigorous than the native genotypes. Rapid growth may account for the quick access of invasive genotypes of P. aculeata to tree canopies. Catorhintha schaffneri damage varied between genotypes but differences in the damage and impact from the agent could not be explained by whether the plant originated in the introduced or native distribution. In sum, while the growth of the invasive genotypes largely conforms to the EICA hypothesis, the impact of C. schaffneri did not support the hypothesis. The influence of host variation in P. aculeata on the fitness of C. schaffneri within the context of local adaptation to plant genotypes from different localities was tested using agent survival, stage-specific and total developmental time, and the extent of damage to ten host genotypes. Maw’s Host Suitability Index (HIS) and Dobie’s Susceptibility Index (DSI) showed the preference by and performance of C. schaffneri on the different genotypes of the plant. Catorhintha schaffneri survived to the adult stage on 70% of genotypes tested. Evidence consistent with the assumption that C. schaffneri would be fitter on the native genotypes than the invasive genotypes due to local adaptation was not found. In addition, there was no evidence in support of fitter agents on the invasive genotypes than on the native genotypes as proposed by EICA hypothesis. Catorhintha schaffneri developed equally well on the invasive genotypes of P. aculeata as on the native genotypes. To establish whether host variation would affect diet selection by C. schaffneri, both nymphs and adults were examined in paired-choice and multiple-choice trials. The nymphs and adults chose their hosts regardless of host genotype differences. The agent may be good at selecting good succulent shoots from bad shoots, but is incapable of distinguishing a good host genotype from a poorer one. This thesis shows, therefore, that P. aculeata and its array of genotypes in South Africa could be effectively controlled by C. schaffneri, as it has the potential to suitably utilise and impact the different genotypes of the weed in South Africa with neither any demonstrable preference nor local adaptation for the native genotypes. Consequently, the use of C. schaffneri, as a biological control agent in the weed biological control programme of P. aculeata remains promising, as the agent is insensitive to the intraspecific variation of the invasive host plants

The Physicochemical Characteristics of Ibiekuma River Ekpoma, Nigeria

The Ibiekuma River is an important source of livelihood to its catchment. It contributes enormously to research success and living standard of students and staffs of the Ambrose Alli University Ekpoma, Nigeria. The aim of the study was to determine the impact of anthropogenic activities on the physicochemical properties of Ibiekuma River. Twenty seven water samples were collected at four stations during the study period and analyzed accordingly. The results obtained shows that the physicochemical parameters of the river were in conformity with the World Health Organization (WHO), National Agency for Food, Drug Administration and Control (NAFDAC) and Nigerian Industrial Standard (NIS) safe limits, except for pH values which ranged from 4.69 to 4.81. The heavy metal concentrations were found to be within the limit of the guidelines prescribed by WHO and NAFDAC. Also, there was no significant difference (P > 0.05) in the concentrations of the physicochemical parameters across the four stations sampled along the Ibiekuma River. Water obtained from Ibiekuma River will be fit for domestic use, only if purified

Eight decades of invasion by Chromolaena odorata (Asteraceae) and its biological control in West Africa: the story so far

Chromolaena odorata (L.) R.M. King and H. Robinson (Asteraceae) is a perennial weedy shrub of neotropical origin and a serious biotic threat in its invasive range. The Asian-West Africa (AWA) biotype of C. odorata present in West Africa is both morphologically and genetically different from the southern African (SA) biotype. The AWA biotype was first introduced into Nigeria in the late 1930s and rapidly spread across West Africa. Currently, 12 of the 16 countries in West Africa have been invaded, with significant negative effects on indigenous flora and fauna. However, locals in West Africa have found several uses for the weed. As chemical, physical and other conventional methods were unsustainable, costly and largely ineffective, three biological control agents, Apion brunneonigrum (Coleoptera: Brentidae), Pareuchaetes pseudoinsulata (Lepidoptera: Erebidae) and Cecidochares connexa (Diptera: Tephritidae), have been released in West Africa between the 1970s and the early 2000s. However, only C. connexa and P. pseudoinsulata established, contributing to the control of the weed, in six and four countries in West Africa respectively. Limited research funding, the absence of post-release evaluations of the established agents, and the ?conflict of interest? status of C. odorata (i.e. being beneficial for local use but damaging to ecosystem services and agriculture), are serious factors deterring the overall biological control effort. Here, using historical records and field surveys, we examine the invasion history, spread, impacts, and management of C. odorata in West Africa and make recommendations for the sustainable management of C. odorata in the region

Eight decades of invasion by Chromolaena odorata (Asteraceae) and its biological control in West Africa: the story so far

Chromolaena odorata (L.) R.M. King and H. Robinson (Asteraceae) is a perennial weedy shrub of neotropical origin and a serious biotic threat in its invasive range. The Asian-West Africa (AWA) biotype of C. odorata present in West Africa is both morphologically and genetically different from the southern African (SA) biotype. The AWA biotype was first introduced into Nigeria in the late 1930s and rapidly spread across West Africa. Currently, 12 of the 16 countries in West Africa have been invaded, with significant negative effects on indigenous flora and fauna. However, locals in West Africa have found several uses for the weed. As chemical, physical and other conventional methods were unsustainable, costly and largely ineffective, three biological control agents, Apion brunneonigrum (Coleoptera: Brentidae), Pareuchaetes pseudoinsulata (Lepidoptera: Erebidae) and Cecidochares connexa (Diptera: Tephritidae), have been released in West Africa between the 1970s and the early 2000s. However, only C. connexa and P. pseudoinsulata established, contributing to the control of the weed, in six and four countries in West Africa respectively. Limited research funding, the absence of post-release evaluations of the established agents, and the ‘conflict of interest’ status of C. odorata (i.e. being beneficial for local use but damaging to ecosystem services and agriculture), are serious factors deterring the overall biological control effort. Here, using historical records and field surveys, we examine the invasion history, spread, impacts, and management of C. odorata in West Africa and make recommendations for the sustainable management of C. odorata in the region

Plant size, latitude, and phylogeny explain within-population variability in herbivory

Interactions between plants and herbivores are central in most ecosystems, but their strength is highly variable. The amount of variability within a system is thought to influence most aspects of plant-herbivore biology, from ecological stability to plant defense evolution. Our understanding of what influences variability, however, is limited by sparse data. We collected standardized surveys of herbivory for 503 plant species at 790 sites across 116° of latitude. With these data, we show that within-population variability in herbivory increases with latitude, decreases with plant size, and is phylogenetically structured. Differences in the magnitude of variability are thus central to how plant-herbivore biology varies across macroscale gradients. We argue that increased focus on interaction variability will advance understanding of patterns of life on Earth