Plutella xylostella

Colour: when disturbed, tiny adults fly from plant to plant. When at rest, three or four diamond-shaped areas formed by two forewings, are visible on the dorsal surface. Pale-green larvae with pale green to brown head capsules or brown pupae covered in white silken cocoons are present on plant parts damaged by P. xylostella.
Size: adult 10-12 mm long, fully-grown larva 10 mm long, pupa 5-6 mm long.
Behaviour: adults fly when disturbed. Larvae curl up when disturbed, or drop from the foliage to the ground.
Traps: adults are attracted to light traps. Adult males are attracted to sex pheromone which consists of three chemicals: (Z)-11-hexadecenal, (Z)-11-hexadecenyl acetate and (Z)-11-hexadecenyl alcohol (Chow et al., 1978). The yellow sticky traps can also be used to monitor populations in the field (Sivapragasam and Saito, 1986).
Food: Major host plants associated with the family Cruciferae with a few host plants in the family Capparidaceae (Idris, 1998;Tanaka et al., 1999).
Scouting Techniques in Oilseed rape
The count method, although often laborious, is currently the most accurate method of estimating P. xylostella population densities in oilseed rape. It involves performing counts of larvae in several locations throughout the field and determining the average population per unit area. Remove plants in an area of 0.1 m 2, beat them onto a clean surface, and count the number of larvae dislodged from the plants. Scout at least five locations per field and monitor crops at least twice weekly (Canola Council of Canada, 2014).
The action threshold in Canadian oilseed rape crops is 20-30 larvae/0.1 m 2 at the advanced pod stage. This works out to approximately two to three larvae/plant, given the plant population is about 100 plants/m 2 (Canola Council of Canada, 2014).
Sweep net sampling and trapping (e.g. sticky, pheromone and bowl traps) can be used to detect the presence and general abundance of P. xylostella in the field, but these tools alone may not provide a reliable estimate of larval density. Nevertheless, high counts in sweep sampling and trapping can prompt growers to use the more accurate 'count method' (Sarfraz et al., 2010;Canola Council of Canada, 2014).
In regions such as Canada where P. xylostella infestations are associated with annual migrations, pheromone traps coupled with wind trajectory models are useful tools to determine the size and timing of the moth flight.
Scouting Technique in Brassica Vegetables
In Brassica vegetable crops, the 'percent infested' threshold scouting technique is more efficient in detecting damaging pest populations as it avoids the need to remove plants and count pests and is relatively easy for growers to use (Berry, 2000). This technique is successfully used to scout several other insect and mite pests in commercial crops.
Various types of traps (e.g. sticky, pheromone, pitfall and bowl traps) can also be used to detect the presence and relative abundance of P. xylostella in the field.