Life cycle, habits and behaviour of Thrips tabaci Lindeman in onions (Album cepa)
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Abstract
Thrips tabaci is considered one of the most important pests that affect onions, mainly be-cause its damage affects both the quality and the yields. One of the objectives of this work was to study the life cycle of T tabaci, under laboratory conditions in Palmira, Colombia (1000 mas' and 23.4°C). The duration in days of each insect stage was: egg 4.6; I nymphal instar 2.06; II nymphal instar 4.03; pre-pupa 1.2. The adults longevity varied between 16 and 24 days. This species presents a parthenogenetic reproductive pattern of the thelytoky type. The female has a pre-ovipositional period of 4-6 days. The oviposition period lasts 15.2 days, but most eggs were laid between the 7th and 12th days. The total amount of eggs produced by a female was 40.65 of which 65.28% were successfully fertilized. In theory, T tabaci has an intrinsic rate of increase of 0.35, a finite rate of increase of 1.43, and an average generation period of 10.49 days. Insect traps of various colors (blue, white, yellow, and violet) were proved in three locations. Most insects were captured in the blue traps and according to the Tukey test, the blue colored traps showed to be statistically different to the others, which presented few differences among themselves. The fluctuation of the population was studied in commercial fields with and without applications. In those with insecticide, the population was controlled until the 8th week, when the application of insecticides was suspended, causing an inmediate increase in the population. In the second case, the population increased constantly, to the point were in the 4th or 5th week after transplantation it caused economic damage. In a field, with insecticides, there exists a high correlation between the population captured in traps and captured on the plants. In the field without insecticides, no correlation seems to exist. The main plant hosts of T tabaci were identified in the onion producing areas of the Cauca Valley.
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