Abstract
The objective of this study was to determine the effects of predators, parasitoids, leaf chemical composition and levels of leaf nitrogen and potassium, total rainfall, mean temperature, sunlight and relative humidity on the attack rate of the whitefly Aleurothrixus aepim (Goeldi) on the cassava plants Manihot esculenta Crantz. It was observed a negative correlation between nymphs of whitefly and mean temperature and nymphs and adults with total rainfall. There were observed relationships between Aelothripidae with eggs, nymphs and adults of whitefly; Encarsia sp., spider Araneidae and Syrphidae with adults of whitefly; and Hyaliodes vitreus with nymphs of whitefly. Ants of the genus Crematogaster were observed associated to nymphs of this whitefly. The peaks 25.503 and 47.763min. (retention time) correlated with whitefly adults. Even though different factors, such as ecological and physiological conditions of plants, besides parasitoids and predators, can affect population fluctuation of the whitefly; the most important one for this insect seems to be the plant phenology (leaf senescense).
Highlights
The cassava (Manihot esculenta Crantz) (Euphorbiaceae) represents an important source of carbohydrates and it is the fourth most important food in the world (Bellotti et al, 1999)
The cassava is usually cultivated by small producers in semi-arid areas with poor rainfall distribution and low fertility soils
One of the most serius cassava pests in Brazil is the whitefly Aleurothrixus aepim (Goeldi) (Homoptera: Aleyrodidae) (Farias, 1994). This insect sucks the sap of cassava leaves, which turns them yellowish and grubbed
Summary
The cassava (Manihot esculenta Crantz) (Euphorbiaceae) represents an important source of carbohydrates and it is the fourth most important food (after rice, sugar and corn) in the world (Bellotti et al, 1999). The cassava is usually cultivated by small producers in semi-arid areas with poor rainfall distribution and low fertility soils. Such conditions and the occurrence of pests and diseases (Bellotti et al, 1999) can reduce its productivity, which can reach 21.3 tons/ha in good growing conditions (Henry, 1995). One of the most serius cassava pests in Brazil is the whitefly Aleurothrixus aepim (Goeldi) (Homoptera: Aleyrodidae) (Farias, 1994) This insect sucks the sap of cassava leaves, which turns them yellowish and grubbed. It transmits virus and its honeydew can serve as substratum for fungi growing. High populations of this whitefly can reduce productivity and their contact can give the cassava a bitter flavour (Farias and Santos Filho, 1996)
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