ABSTRACT
The objectives of this work were to assess the infestation of ten genotypes of cassava by the shoot fly Neosilba perezi (Romero & Ruppell) and to investigate effects of plant age, temperature or precipitation on cassava plants infestation by the shoot fly. Thirty-two individuals of each cassava genotype were planted and analyzed every two weeks in order to calculate the percentage of plants infested by shoot fly larvae at each sampling event and per genotype. Infestation by the fly was different across the genotypes. Genotype IAC Caapora 105-66 and genotype IAC Cascuda were resistant to shoot fly infestation, whereas the genotype IAC 15 was the most susceptible to this insect. Plant age may have an influence on infestation by shoot flies. Advanced plant age apparently favors lower or even inexistent infestation rates. However, infestation rate does not seem to be affected by temperature or precipitation.
Subject(s)
Animals , Diptera , Manihot/genetics , Manihot/parasitology , GenotypeABSTRACT
Among the pests of cassava, the shoot fly, Neosilba perezi (Romero & Ruppell), is one of the most prevalent. It attacks mainly the terminal shoots and causes infested plants to produce lateral shoots. Reports on this species are rare or inexistent; thus, the purpose of this study was to assess three different areas for N. perezi infestation. The survey began in March 2008 and finished in February 2009. Fortnightly analyses were performed starting 45 days after planting, calculating the rate of infestation by N. perezi larvae in each study area. The areas were correlated separately for each parameter: fortnightly mean temperature, fortnightly mean rainfall, and plant age. The N. perezi larvae occurrence rate was higher in area 1 - which presented the highest population peaks in autumn and winter. There was only a single population peak in area 2, in winter; and area 3 presented the weakest population peak among the three, in November. The shoot fly population dynamics in the studied region is separately correlated to temperature, rainfall and plant age: temperatures above 23ºC, relatively high rainfall and older plants seem to have a negative effect on populations of this insect.