Brassica is a genus of plants in the mustard family that includes cauliflower, sprouts, broccoli and cabbage. Plants of the brassica family are rich sources of biologically active substance. The beneficial effects of brassica vegetables on human health have been somewhat linked to phytochemicals. They prevent oxidative stress, induce detoxification enzymes, stimulate immune system and decrease the risk of cancers. Crucifers are the important winter crops grown widely in tropical and temperate regions of the world, giving yield of 50.7 million tons. It is cultivated around the year over an area of 8263 hectares in Karnataka with production of 23.63 tons per hectare. Cauliflower and cabbage are the most common crops throughout the world. Diamondback moth (DBM) caused losses of about 16 million dollars by causing a 2.5% damage annually. There are many insect pests that attacked these crops and most common are diamondback moth, tobacco cutworm, aphid, jassid, cabbage worm and many others. The most important of these insect pests is the diamondback moth Plutella xylostella also called cabbage moth that belongs to Plutellidae. There are many controlled strategies including chemical control, biological control, physical control and many other methods. This study contributes to the literature offering understandings about the insect pests of brassica and their best management techniques.
- insect pests
Cruciferous family crops are economically important, and especially cabbage (
2. Bionomic of diamondback moth
2.1. Biology and ecology
DBM is a tiny brownish color moth having triangular markings on their forewing. Eggs are laid signally on the underside of leaves. The female of diamondback moth lays 300 eggs in her reproductive period. The female of DBM lays eggs on the lower and upper side of the leaf surface and the ratio is 3:2, and very little amount of eggs are laid on the stems of the leaf . An egg hatching period is 2–4 days. As new tiny larvae emerge, they start feeding on the lower side of leaves. Larval duration is 10–15 days but it largely depends on the temperature and other environmental conditions. Color of young larvae is from whitish yellow to pale green. The life of an adult is 10–15 days. Larvae cause large defoliation of leaves . Diamondback moth adult is a weak flier and the length of adult moth is about 5 mm and width is 2 mm .
After the emergence, the first instar makes mines in the spongy tissue and the second instar starts feeding on the lower side of the leaf and consumes all the tissue expect the waxy layer. When fourth instar feeding is complete, it converts into a cocoon-like structure that is called the pupal stage, and at this stage feeding stops . The duration of this stage depends upon the temperature and mostly it is 4–10 days, but it can decrease in warm areas and increase in cold areas; after adults emerge who feed on water or dew drops, their adult life is short .
In subtropical and tropical regions, where the cabbage and cauliflower or any other crops belonging to the Crucifers family are grown throughout the year, all the stages of diamondback moth are present at any time. In the temperate region, where the crucifers crop are not grown throughout the year, and in winter season, both pupal and adult stages of diamondback moth hibernate in plant debris . A study was done in the New York state for the presence of diamondback moth during winter season using different pheromone traps and it found that no diamondback moths were caught .
Diamondback moths have great abilities to disperse and migrate over long distances. Mass migration of DBM occurs in Britain, and the adult of diamondback moth migrates from Baltic to Southern Finland and covers about 3000 km, and this study indicates that the adult of DBM remains in flight continuously for several days .
3. Distribution of diamondback moth
Diamondback moth has been recorded all over the world and the largest number of this species was recorded in the USA. Seven species of this insect was recorded in South America and Argentina, Chile and Colombia recorded nine species and only two species of
4. Damaging history of diamondback moth
Diamondback moth is a serious pest of cruciferous plants worldwide and about 1 billion dollars of losses occur annually due to its larval damage . It is reported that 90% of losses occur due to this pest  and also reported that 60% loss occurs in production and 2 billion dollars of losses occur when controlling this pest . It is estimated that 16 million dollars of losses occur on the basis of a 2.5% damage on protective crops per annum by this pest . The larvae of DBM caused damage to all cruciferous family crops especially cabbage in Southeast Asia.
The failure of DBM occurred when this insect became the most destructive pest of the Lepidopteran family. DBM damaged above-ground plant parts and reduced the yield except during rainy weather . When the attack of diamondback moth is very serious the losses reach up to 80–90% .
4.1. Mode of damage
The larvae of diamondback moth
5. Chemical control of diamondback moth
There are many specific insecticides used for the control of DBM while certain chemicals are more effective against other pests as compared to DBM, so it is important to select appropriate chemicals according to insect pests. Some chemicals having longer residual action on later growth stages like prothiophos, cartap and fenvalerate mixtures are suitable for management of diamondback moth . Organophosphates (OPs) have been considered as the most important group of compounds for the control of DBM. In OP groups, enough variations in chemical structures have contributed to the wide spectrum of efficacy and varied levels of resistance observed in DBM .
Many synthetic pyrethoids (permethrin constituting 0.01%, decamethrin of 0.004%, fenvalerate of 0.01% and cypermethrin of 0.005%) have no good results for controlling after 48 h of the treatment on adult diamondback moth while quinalphos constituting 0.05%, phosalone of 0.05%, endosulfan of 0.05%, monocrotophos of 0.05% and dichlovos of 0.05% have greater toxic effects on both adult and larval stages; after 6 h dichlovos and quinalphos recorded 100% mortality, endosulfan 93% and monocrotophos 63% . Spinosad and permethrins caused 100% mortalities to diamondback moth adults and larvae in leaf dip and residual bioassays method after 72 h of treatment .
Spinosad and fenvalerate provide good results for the control of diamondback moth larvae at various development stages. Novalurin at 6–12 oz./acre is effective for the control of DBM as compared to non-treated plants, and spinosad is superior to all other insecticides for controlling DBM . Emamectin benzoate with trademark PROCLAIMR is extensively used in the USA and has great degradation on leaf surface and provides good control of DBM larvae and other pest species . Benzoyl phenyl urea and chitin synthesis inhibitors also show good results for controlling resistance-developed population of diamondback moth [25, 26].
5.3. Neem-based insecticides
Neem-based insecticides are most effectively used for the management of
6. Biological control of DBM
There are many biological control agents used for the control of diamondback moth including parasitoids and bio-pesticides . In 1998, the main focus was on introducing the two important species of parasitoids, that is,
Mixture of some chemical and Bt products is very useful for the control of diamondback moth. There is belief that such mixtures are also useful and have large potential for the control of Crucifer insect pests. Similar results was reported as mention above by the use of mixture of typically 20 chemicals formulations . The mixture of Bt products and parasitoids
6.1. Egg parasitoids
6.2. Larval parasitoids
6.3. Pupal parasitoids
7. Bacterial control of DBM
8. Nematodial control of diamondback moth
Entomopathogenic nematodes in families Steinernematidae and Heterorhabditidae have great effects for controlling the Lepidopteran pest and the best alternative control by insecticides . It is reported that Steinernematidae,
9. Viral control of diamondback moth
Granulosis virus (PxGV),
10. Resistance against different control strategies
One of the major reasons for the development of resistance to insecticides by DBM is the increasing of number of sprays and thereby increasing cultivation costs. Eco-friendly and less-toxic new chemicals are also available in the market but the farmers are still using broad-spectrum pyrethroids, organophosphates, organochlorines and many other conventional insecticides diamondback moth has developed resistance against these insecticides . Thiodicarb, fipronil, lufenuron, spinosad, carbosulfan and indoxicarb are still performing well as compared to malathion . In Malaysia, high uses of abamectin in Crucifer crops against diamondback moth develop serious problems of resistance .
High rate of resistance developed in many insecticides such as cypermethrin, pyrethroids, fenvalerate, organophosphate, deltamethrin and quinalphos was found in DBM population, collected from areas where farmer used mostly pyrethroids at heavy doses . Diamondback moth has developed resistance against fenvalerate, cypermethrin and deltamethrin in the Indian province of Punjab . A new chemical cartap hydrochloride is a successful insecticide for controlling resistance population of DBM. A 170-fold resistance to quinalphos developed in DBM .
In some part of the world, DBM became most difficult insects to control because of development of resistance due to the use of extensively toxic chemicals [56, 57]. The extensive use of toxic commercial insecticides against DBM in India is the one of the major constrains in the profitable cultivation of cole crops because these chemicals in heavy and toxic doses developed resistance in DBM . Both mechanisms of resistance and baseline susceptibility are necessary for the effective management of location-specific resistance strategies [59, 60].
Resistances developed 144-fold against diamondback moth due to the use of cyperpethrin at Panipat (Haryana) in India . In DBM, resistance persisted longer in Taiwan against pyrethroids . It is reported that
The larvae of South Texas strain were less susceptible to indoxacarb than that of the Minnesota strain, and mortality increased with the time of exposure . It is reported that there is no significant difference in the laboratory strain and field population when comparing the resistance . Outside Southeast Asia, it has been reported that there is great development of resistance in this insect pest in several countries, for example, Japan, the USA, Honduras and Australia . In some regions it has been also detected that DBM developed resistance against IGRs which are so-called benzoylphenyl urea (BPUs) .
It is documented that difference between two populations of DBM at LC50 was 2.9 fold and high levels of resistance developed in DBM against lambda-cyhalothrin and lufenuron . In China, LC50 of 1.22, 0.61 and 0.004 ppm against emamectin benzoate from His-Hu strain and Lu-Chu strain and susceptible strain .