Bad bugs banished
Integrated Pest Management
The Botanic Garden seldom uses pesticides. The roses are rarely sprayed with fungicides - only on an as-needed basis - and the Garden's nursery uses no toxic sprays at all.
Any bug is bound to have another bug that preys on it and detecting and encouraging the right predator is an important part of how Integrated Pest Management (IPM) works.
Beneficial wasp Encarsia formosa has been very successful in the nursery and Begonia House. This wasp lays eggs in whitefly nymphs or in scale crawlers, giving its larvae
a guaranteed food supply and keeping populations of these pesky insects down.
Another parasitic wasp, Thripobius semileutus, is raised on a population of thrips that, in turn, are raised on unripe lemons. This tiny helper is just 0.6mm long.
Mealybugs are given homes in plastic boxes containing old sprouted potatoes, the black and orange ladybird Cryptolaemus montroizieri is put in the boxes and a month later around 200 young ladybirds are ready to be moved (using care and good eyesight because ladybird larvae look very similar to mealybugs) into the glasshouses, where one ladybird can eat 50 mealybugs a day.
When the nursery stopped using toxic sprays many other beneficial insects moved into the area, including lacewings, ladybirds, cockroaches (little cockroaches love to dine on aphids), hoverflies, other aphid and scale parasites, assassin bugs, praying mantis, predatory mites and spiders.
Temperature and life-cycles are important in both pest control and beneficial insect growth. Pest numbers increase rapidly in spring. Some insects multiply faster at a certain temperature, while their predators might multiply fastest at a different temperature. Bio-control is very much a balancing act!
You also need to keep a few pests around to sustain beneficial insects - other than snacking on nectar occasionally, they do not eat plants. Some species that are really popular with pests, such as Rosa multiflora, are kept in the nursery as 'banker' plants - likened to bank storage vaults - to maintain pest populations so that the beneficial insects always have something to eat. The aim of IPM is to reduce pest numbers to an acceptable level, rather than to get rid of them completely.