Invasive Pest- Diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae)

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is one of the most destructive cosmopolitan pests of cruciferous crops. It is one of the most studied insect pests in the world, yet it is among the 'leaders' of the most difficult pests to control. P. xylostella requires US$ 1.0 billion globally in estimated annual management costs (Talekar & Shelton 1993) in addition to the crop losses estimated US$4-5 billion annually.

P. xylostella is a highly invasive species. This crucifer specialist may have its origin in Europe (Hardy 1938), but on the basis of the presence of its biocontrol agents (14 species of parasitoids) and host plants (175 species, of which 32 are exotic), Kfir (1998) speculated that it originated in South Africa. Using similar arguments, Liu et al. (2000) are of the view that P. xylostella originated in China. This pest is now present wherever its host plants exist and is considered to be the most widely distributed of all Lepidoptera (Shelton 2004). It is highly migratory and wind-borne adults can travel long distances to invade crops in other regions, countries and continents. Immature stages also hitchhike on plant parts and can establish in new areas. Climate change is expected to cause range shifts and change the population dynamics of P. xylostella and its parasitoid associates.

Life Cycle

Many reports describe the seasonal abundance of diamondback moth in relation to different climatic conditions (Harcourt, 1957; Shaw, 1959; Wu, 1968; Iga, 1985). Although the moth breeds throughout the year in tropical conditions, the species, along with many other leaf-feeding insects, infests cruciferous crops during the cool and dry season. Heavy rain appears to be detrimental to infestation (Talekar and Lee, 1985).

Total development time from the egg to pupal stage averages 25 to 30 days, depending on weather, with a range of about 17 to 51 days. The number of generations varies from four in cold climates such as such as Ottawa, Canada (Harcourt, 1957) to 10-14 generations in the tropics (Hardy, 1938; Bonnemaison, 1965; Abraham and Padmanaban, 1968; Koshihara and Yamada, 1981)

Host Plants

Diamondback moth attacks only plants in the family Cruciferae. Virtually all cruciferous vegetable crops are eaten, including broccoli, Brussels sprouts, cabbage, Chinese cabbage, cauliflower, collard, kale, kohlrabi, mustard, radish, turnip, and watercress. Not all are equally preferred, however, and collard will usually be chosen by ovipositing moths relative to cabbage. Several cruciferous weeds are important hosts, especially early in the season before cultivated crops are available.

Insecticide Resistance

The diamondback moth was the first crop insect reported to develop resistance to microbial Bacillus thuringiensis insecticides. The diamondback moth was the first crop insect reported to be resistant to DDT and now, in many crucifer producing regions, it has shown significant resistance to almost every synthetic insecticide applied in the field, including the most recent groups such as diamide. In certain parts of the world, economical production of crucifers has become almost impossible due to insecticidal control failures. Consequently, increased efforts worldwide have been undertaken to develop integrated pest management (IPM) programs, principally based on manipulation of its natural enemies. (Mohammad Sarfaraz,2007)

Novel Control Program

Looking at pesticide resistance status and the failure of Bacillus thuringiensis and synthetic insecticide molecules to control the population of Diamondback moth, a sustainable containment strategy based on integrated pest management is recommended. During open field trials in cabbage fields; our IPM tool AI-Enabled insect-pest control device BraveHawk® Monza in combination with release of biological control agent "Trichogramma brassicae" have shown excellent results. This integrated approach brought down the population of diamondback moth well below economic threshold level (ETL) and kept yield losses well below 3%.