Horticultural pests Life cycle. The 1 mm long, narrow-bodied insect has feather-like wings. The last instar of the life cycle, called the pupa , descends to the soil, and it is this stage which overwinters. In greenhouses there may be seven generations per year, while outdoors one life cycle is common. Spread. Adults may be blown considerable distances from nursery to nursery in the wind. (The occurrence in Britain of Western ower thrip (Frankliniella occidentalis ) on both greenhouse and outdoor ower and vegetable crops has created serious problems for the industry, particularly because it transmits the serious tomato spotted wilt virus, and is able to pupate on the plant, deep within dense owers such as carnation.) Control. Thrips infestations may be reduced in greenhouses by the use of ne screens over vents, and by a double door system.

Amateur gardeners are able to use a recently introduced product for thrip control containing natural plant extracts which block the insects breathing holes. Professional growers use the predatory mite Neoseiulus cucumeris , and the predatory bug Orius laevigatus. Chemicals used include the ingredient abamectin and the above named natural plant extract . Western ower thrip has shown greater resistance to chemical control than the other thrips and a careful rotation of chemical groups has proved necessary. Earwigs ( Forfi cula auricularia )

These pests belong to the order Dermaptera, and bear characteristic pincers (cerci) at the rear of the 15 mm long body. They gnaw away at leaves and petals of crops such as beans, beet, chrysanthemums and dahlias, usually from July to September, when the nymphs emerge from the parental underground nest. They usually spread by crawling on the surface of the soil, but they can also y. Upturned ower pots containing straw are sometimes used in greenhouses for trapping these shy nocturnal insects. The professional grower may use pirimiphos-methyl as a spray or smoke.

Moths and butterfl ies This group of insects belongs to the large grouping, the Endopterygota (see p205) which has different life cycle details from the aphid group. The order (Lepidoptera) characteristically contains adults with four large wings and curled feeding tubes. The larva ( caterpillar) , with six small legs and eight false legs, is modi ed for a leaf-eating habit (see Figures 14.6 and 14.7 ). Some species are specialized for feeding inside fruit (codling moth on apple, see Figure 14.15 ), underground (cutworms), inside leaves (oak leaf miner), or inside stems (leopard moth). The gardener may nd large webbed caterpillar colonies of the lackey moth (Malacosoma neustria ) on fruit trees and hawthorns, or the juniper webber ( Dichomeris marginella ) causing webs and defoliating junipers. 213 214 Principles of horticulture (a) (b) Figure 14.13 (a) Cabbage-white adult . (b) Yellow underwing moth with cutworm larva and brown