Trichoplusia ni (Hübner)
Common name: Cabbage looper, the ni moth.
Systematic position: Insecta, Holometabola, Lepidoptera, Noctuidae.
Geographic distribution: Almost cosmopolitan.
Morphology: Body of adult about 15 mm long, the forewings are red-brown with a silvery mark
resembling the letters U or Y; hindwings gray-brown. The larva has 3 prolegs (therefore “looper”“), is up to 30 mm long, greenish with a paler lateral stripe and a darker ldorsal line.
Life history: The moths are active at night, feeding on nectar of flowers. A female lays 350 or more eggs singly, on the upper surface of leaves, whereon the emerging larvae (caterpillars) feed. They move about by holding on to the leaf with their forelegs, arching the body and thus bringing the posterior legs forward (thus “loping”). The threshold of development is around 10-12°C, and there are usually five annual generations. Pupation usually takes place in leaf litter and crop debris.
Host plants: This pest feeds on over 160 species of plants in 36 families, especially of the family Brassicaceae (Cruciferae), with a preference for cabbage and also other crops, like tomatoes.
Economic importance: This looper is a serious pest of many Brassicaceae, especially cabbage. The young larvae feed on the lower sides of leaves, their gnawing leaving “windows” in the leaf, whereas elder larvae chew larger holes in the leaves. Young plants may be killed if the growing point is damaged, or its injury is manifested by branching. Other damage consists of feeding on or in the head and contaminating it with frass. If not controlled, the larvae remain within broccoli heads at harvest and because they cannot easily be washed out, will go to market with the broccoli. Damage to tomatoes includes feeding on the leaves which exposes the fruit to the sun, resulting in sun scald.
Management
Monitoring: Various traps, using blacklight and/or pheromones have been used, singly or combined, to predict pest population densities. Looper presence is suspected when insect-eaten leaves, from which “windows” have been eaten are found.
Horticultural methods: Row covers, if economically practical, are effective at preventing the moths from depositing eggs on crops.
Plant tolerance: Red cabbage appears to be relatively tolerant, but that may be dissipated under heavy pest pressure. Early maturing broccoli cultivars were less attacked as compared to those that mature late.
Chemical control: The cabbage looper has developed much resistance to insecticides, whose intensity varies among locations. Neem and pyrethroids are effective, especially if applied during the early larval stages. Commercial compounds of Bacillus thuringiensis (Bt) often control the small larvae, but the pest is developing resistance to Bt. Another product is “Loopex”, which contains the specific T. ni nuclearpolyhedrosis virus (known as “Trichoplusia ni single nucleopolyhedrovirus”, abbreviated to TnSNPV), to which the pest is also developing resistance. Various botanical compounds have been assayed with uneven results.
Biological control: Many parasitoids and microorganisms attack the pest in different parts of the world, and are sometimes the main factors affecting looper populations. Major parasitoids include the polyembryenic Coptisoma truncatellum (Dalman) (Encyrtidae, Trichogramma spp. (Trichogrammatidae) , and the tachinid Voria ruralis (Fallen). The best known microorganism is the specific _“Trichoplusia ni_PNV”, which may cause considerable pest mortality. Undetermined fungi can kill about 10% of the population. The effectiveness of the microorganisms may vary according to the crop that they are meant to protect.
References
Akhtar, Y., Yeoung, Y.-R. and Isman, M.B. 2008. Comparative bioactivity of selected extracts from Meliaceae and some commercial botanical insecticides against two noctuid caterpillars, Trichoplusia ni and Pseudaletia unipuncta. Phytochemical Review 7: 77–88.
Ali, M.A., Abdel-Salam, A.L., Gadallah, A.I. and El-Khouly, A.S. 1988. Influence of host plant on the development and annual generations of the cabbage looper Trichoplusia ni (Hb.) in Egypt. Journal of Applied Entomology 106: 297–301.
Dickson, M.H. and Eckenrode, C.J. 1975. Variation in Brassica oleracea resistance to cabbage looper and imported cabbage worm in the greenhouse and field. Journal of Economic Entomology 68: 757-760.
Lindgren, P.D. and Greene, G.L. (eds). 1984. Suppression and management of cabbage looper populations. USDA Technical Bulletin 1684.
Milks, M.L., Myers, J.H. and Leptich, M.K. 2002. Costs and stability of cabbage looper resistance to a nucleopolyhedrovirus, Evolutionary Ecology 16: 369–385.
Oatman, E.R. and Platner, G.R. 1971. Biological control of the tomato fruitworm, cabbage looper, and hornworms on processing tomatoes in southern California, using mass releases of Trichogramma pretiosum. Journal of Economic Entomology 64: 501-506.
Sarfraz, R.M., Cervantes, V. and Myers, J.H. 2010. Resistance to Bacillus thuringiensis in the cabbage looper (Trichoplusia ni) increases susceptibility to a nucleopolyhedrovirus. Journal of Invertebrate Pathology 105: 204-206.
Soo Hoo, C.F. and Seay, R.S. 1972. Effects of parasitism by Voria ruralis on the feeding behavior of larvae of Trichoplusia ni. Israel Journal of Entomology 7: 37-40.