Factors affecting the presence of Typhlodromusspp. (Acarina: Phytoseiidae) in the calyx cavities of apple fruits and implications for integrated pest management
Predatory mites of the family Phytoseiidae include several species of importance as biological control agents of phytophagous mites in various crops including apples. We report on the post-harvest presence of the motiles of two species, Typhlodromus occidentalis and Typhlodromus pyri, in the calyx cavities of apple fruits of three cultivars. The mean numbers of motiles per fruit were as high as 6.10. The phytoseiid densities were lowest in cv. Bonza and tended to be greater in samples taken in late autumn, particularly in cv. Red Delicious. No significant effect (p > 0.05) was observed for different insecticide treatments. Phytoseiids remained present within fruits of cv. Granny Smith left on the orchard floor in winter. Together with an observed reduction in the numbers of T. occidentalis in the early spring, this suggests that fruits constitute an overwintering refuge. The findings are discussed in relation to the implications for biological control, in particular the minimization of the removal of natural enemies from orchards.
Living at the threshold: Where does the neotropical phytoseiid mite Typhlodromalus aripo survive the dry season?
The establishment of the neotropical predatory mite Typhlodromalus aripo in sub-Saharan Africa has resulted in broadly successful biological control of the cassava green mite Mononychellus tanajoa throughout the cassava belt of Africa. In some mid-altitude areas and drier lowland savannahs of sub-Saharan Africa, which are characterized by cool or hot long (≥5 months) dry seasons, the predator disappears from its habitat in the cassava apex during the dry season and reappears after the onset of rains. It is not known, however, where the predator remains during this time period. In this study, we conducted a field enclosure experiment of cassava plants with the objectives to determine if (a) T. aripo survives at very low densities in the apex, if (b) it survives in the soil or leaf litter below the cassava plant, and if (c) it recolonizes the cassava plant from the surrounding vegetation. Towards the end of the dry season, when the predators had disappeared from all cassava plants included in the experiment, five treatments were applied: (1) plants without enclosure; (2) plants with enclosure; (3) plants with enclosure, apices removed; (4) plants with enclosure, glue barrier around stem; and (5) plants kept free of T. aripo, without enclosure. Predator (re)appearance on cassava apices was monitored non-destructively at weekly intervals and was expressed as the proportion of plants with at least one apex with T. aripo per total number of plants of the treatment. The predators reappeared first on the plants of the treatments (1), (2), and (4). With a time lag of 7–8 weeks, the predators appeared also on the plants of the treatments (3) and (5). The time pattern of the predator’s (re)appearance in the cassava apex of the different treatments suggests that (a) T. aripo survives the dry season in very low densities in the cassava apex; this result is supported by an assessment of the efficiency of non-destructive visual in-field apex inspections which proved that about 10% of the cassava apices that had T. aripo were not recognized as such; (b) T. aripo does not survive in the soil or leaf litter, but we did document cases in a screenhouse experiment, where few individuals migrated down to the ground and walked over exposed soil until they reached the apex bouquet traps; additionally, microclimate measurements in various cassava plant strata proved that the cassava apex and the cassava stem base are the locations with the highest relative humidity during the dry season—which makes the stem base a potentially interesting refuge; (c) T. aripo does not survive in the surrounding vegetation, which is supported by a vegetation survey, where T. aripo was not found on any other plant species than cassava.
Population and Settlement
Part 1 Population distribution: world population distribution variations in world population distribution population distribution in the Highlands and Islands population distribution in Japan population distribution in Brazil. Part 2 Population growth and movement: population structure the world population explosion variations in population growth migration why do people migrate types of migration in North and West Africa West German migration populating the USSR populating Australia attitudes to population control population and natural resources. Part 3 Settlements: location of settlement settlement types settlement functions settlement patterns South Wales valley settlements the changing village. Part 4 Urbanization: million cities world urbanization rural-urban migration in the developing world urban land use inner city problems urban transport the Tyneside metro spheres of influence changing shopping habits the Dutch Randstad Lagos - a city in the developing world new and expanding towns in the UK new settlements in developing countries green belts or red bricks? Part 5 Further studies: UK population migration Kenya's population problems Sheffield Washington New Town.