Infestation

About: Infestation is a research topic. Over the lifetime, 8308 publications have been published within this topic receiving 82305 citations.

Competition in Cereal Aphids (Homoptera: Aphididae) on Wheat Plants

Abstract: The cereal aphids Rhopalosiphum padi L. and Sitobion avenae (F.) coexist on the same host plant but occupy different ecological niches. R. padi arrives first in the season and reaches its population peak before S. avenae. In addition, R. padi prefers the stem and lower leaves, whereas S. avenae is found mostly on the ears and upper leaves of the plant. In greenhouse experiments, the likelihood of competition between R. padi and S. avenae on wheat seedlings and tillering plants was evaluated. The reproductive rate of S. avenae on tillering plants was negatively affected by previous infestation by R. padi, and this effect was larger when R. padi infestation started at an earlier plant growth stage. Likewise, previous infestation by R. padi decreased S. avenae reproduction on seed- lings. In contrast, previous infestation by S. avenae on the flag leaf of flowering plants did not affect R. padi on that plant part. When both aphid species co-occurred from the beginning, the presence of either aphid species negatively affected the reproductive rate of the other. R. padi consistently had a higher rate of population increase than S. avenae. The presence of the other aphid species did not affect within-plant aphid distribution or alate aphid production. Results were similar on wheat seedlings and tillering plants. Finally, alate S. avenae preferred uninfested seedlings over R. padi- infested ones, whereas no preference was observed when the experiment was performed with tillering plants.

Body size and habitat as determinants of tick infestations of wild ungulates in South Africa

Abstract: The purpose of the present work was to test the hypothesis that the intensity of tick infestation on South African wild ungulates is proportional to surface area of the host (body weight0.67) and to assess the role of habitat preference on the intensity of infestations. The results support previous suggestions that larger ungulates are more important hosts for adult ticks, however, the intensity of infestation of nymphs and larvae is proportional to the surface area of the host. Grazers had a lower intensity of infestation than browsers and intermediate feeders. The difference was most pronounced in the 30 to 150 kg weight range within which the grazers were predominantly short-grass grazers which utilize habitat less suitable for ticks. These patterns appeared to be consistent within the three major collection areas, Kruger National Park, KwaZulu-Natal and Mountain Zebra National Park.

Insect pests and beneficial arthropod populations under different hedgerow intercropping systems in semiarid Kenya.

Abstract: Exploiting the principles of biological control of crop pests is an important management strategy for the resource-poor smallholder farmers of the tropics. The effects of nine hedgerow species on the abundance of major insect pests of beans and maize, and predatory/parasitic-arthropods were monitored over two cropping seasons and the intervening dry period. The tree/shrub species evaluated were Gliricidia sepium, Grevillea robusta, Senna siamea, Senna spectabilis, Flemingea congesta, Croton megalocarpus, Morus alba, Calliandra calothyrsus and Lantana camara. Arthropod abundance was monitored through counts of infested plants and using yellow pan and pitfall traps. Beanfly (Ophiomyia spp.) infestation was significantly higher in the presence of hedgerows (35%) than in their absence (25%). Hedgerows did not influence aphid (Aphis fabae) infestation of beans. In contrast, maize associated with hedgerows experienced significantly lower stalk borer (Busseola fusca and Chilo spp.) and aphid (Rhophalosiphum maidis) infestations than pure maize, the margin of difference being 13% and 11% respectively for the two pests. Ladybird beetles closely followed their prey, aphids, with significantly higher catches in sole cropped-plots than in hedgerow-plots and away from hedgerows. Activity of wasps was significantly greater close to hedgerows than away from them. Spider catches during maize season were 77% greater in the presence of hedgerows than in their absence, but catches during other seasons were similar between the two cropping systems. Differences among hedgerow species were not significant for most of the arthropods monitored, except that beanfly infestation was greater with Gliricidia hedgerows. The study indicates that the effect of hedgerows on pest infestations of crops and their role as refugia for predators cannot be generalized but depends on the specific arthropods.

Mechanisms contributing to the competitive success of the invasive fruit fly Bactrocera invadens over the indigenous mango fruit fly, Ceratitis cosyra: the role of temperature and resource pre‐emption

Abstract: We investigated the influence of temperature and infestation sequence on interspecific competition between two fruit flies: an invasive (Bactrocera invadens Drew, Tsuruta '' White, (B) and a native (Ceratitis cosyra Walker, C) (both Diptera: Tephritidae) species. Mango fruits [Mangifera indica L. (Anacardiaceae)] were co-infested with larvae at different constant temperatures (15, 20, 25, and 30 °C) and relative humidity of 50 ± 8%, using different infestation sequences at each temperature (BC together; BC/CB 1, 2, and 3 days apart). There were significant effects of competition in most experimental treatments, resulting in reduced larval survival, pupal mass, and adult emergence for both species. At most of the infestation/temperature combinations, C. cosyra was clearly the inferior competitor. The only exception was at 20 °C when the outcome depended on the sequence of infestation: no C. cosyra survived when the sequence was BC, but more C. cosyra than B. invadens survived when it was CB. At 15 °C, all C. cosyra larvae died, while the development of B. invadens was prolonged and adult emergence reduced. We conclude that resource pre-emption and fluctuations in temperature in mango agroecosystems help to explain observed shifts in dominance between B. invadens and C. cosyra on mango in many parts of Africa. The small window of competitive superiority for C. cosyra at 20 °C and CB infestation sequence, together with other factors such as fecundity and alternative hosts, may allow for co-existence in some environments.

Effects of salmon lice infection on the behaviour of sea trout in the marine phase

Abstract: Salmon lice Lepeophtheirus salmonis Kroyer may affect survival and growth of anadromous salmonids through physiological stress and/or behavioural changes. Using acoustic telemetry tracking, we investigated the behaviour of 30 infected sea trout Salmo trutta throughout the summer in a fjord with very high salmon lice infection pressure. Most of the tracked sea trout adopted a movement pattern expected to suppress salmon lice infestation, as they showed a strong preference for fresh or brackish water, spending most of the time close to a river outlet or even migrating into the river. Highly infested sea trout preferred shallower depths, associated with lower salinity. The fish lost to predation stayed further away from the river outlet than non- predated fish, and were likely subjected to a stronger infection pressure. Half of the tracked group were treated with a salmon lice prophylaxis, emamectin benzoate. The effect of treatment on infestation was monitored in a separate group held in a sea cage and found to be moderate; the mortality in this group was associated with infestation by motile lice stages. In contrast, treatment was not found to have an effect on tracked fish behaviour. It is likely that some physiological and behavioural responses to high salmon lice infection pressure may be present even after a prophy- laxis treatment, in particular when the treatment is given after exposure to salmon lice infection. We conclude that increased salmon lice infection pressure associated with altered salmon farming practice may have the potential to influence the marine behaviour and growth of sea trout.