Abstract
This study evaluated the symptoms of attack by the green belly stink bug, Dichelops melacanthus (Dallas, 1851), in conventional and transgenic commercial corn ( Zea mays ) hybrids, the seeds of which were either treated using the insecticide thiamethoxam or without chemical treatment. The experiment was conducted during the 2010/2011 crop season in Pindorama, Sao Paulo State, Brazil. The percentage of plants with symptoms or injuries was recorded by visually evaluating the degree or intensity of attack symptoms. The height of the plants was also recorded on a weekly basis, until the plants were 40 DAE. We also measured yield compounds, such as the number of rows of grain/spikes, spike weight (with and without straw), and grain weight. The seeds of hybrids that had previously been treated with thiamethoxam showed lower percentage of the number of plants that were attacked. Further, the grain weight of the plants increased 29.5% more than that of plants from untreated seeds. It was also found that transgenic hybrids exhibited lower height reduction in 40 DAE plants than did conventional isolines. Visual inspection is effective in assessing the degree of injury caused by attacks to the developing plants.
Highlights
The percentage of attacks on plants grown from seeds treated with insecticide was significantly lower (61%) than that on plants grown from untreated seeds (86.5%)
Conventional and transgenic hybrids respond differently to D. melacanthus attack, and conventional hybrids exhibit a greater reduction in height
The results indicate that the conventional hybrid 2B710 is more susceptible to attack by D. melacanthus than that the other hybrids
Summary
Manfredi-Coimbra et al (2005) reported that this insect has been considered a secondary pest of the soybean (Glycine max (L.) Merrill) for several years, but has recently become a key pest of corn and wheat (Triticum aestivum L.) Another factor that may have contributed to the significant increase of D. melcanthus in corn is the major use of Bt hybrids, as with the adoption of this technology is to reduce the number of insecticide applications of broad spectrum. Greene et al (2001) observed that these same conditions led to the significant increase in bedbug Euschistus servus in the southeastern United States The damage that this D. melacanthus cause in corn is greater in the early stages of the plant’s development, due to sap sucking and the introduction of salivary toxic enzymes into the stem base of seedlings and plants, resulting in the withering of leaves, and eventually, of the whole plant (Gallo et al, 2002). On the beginning of the development, corn is more affected by stinkbugs attack (BIANCO, 2004), and up to sixth leaves completely extended, corn plants define their yield (FANCELLI; DOURADO NETO, 2000), highlighting the importance of these insects on corn plants
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