Development of a treatment threshold for sucking insects in determinate Bollgard II transgenic cotton grown in winter production areas

Little is known about the impact of sucking insects on cotton grown in tropical production areas. To examine this, an experiment was conducted at Katherine in northern Australia to determine the impact of mirids (Creontiades dilutus (Stål) and Creontiades pacificus (Stål), green vegetable bug (Nezara veridula (L.)) and red‐banded shield bug (Piezodorus hybneri (Gmelin)) on the yield and fibre quality of the transgenic cotton variety DP50bx containing genes for the expression of Cry1A(c) and Cry2A(b) δ‐endotoxins of Bacillus thuringiensis Berliner variety kurstaki. The trial examined the impact of sucking insect populations in the range 0.5–2.0/m2. Yields of unsprayed plots were approximately 30% of those obtained in plots sprayed on a threshold of 0.5/m2 which did not differ significantly from plots sprayed regularly to exclude sucking insects. The increase in yield in the low pest density treatments was the result of improved fruit retention in the middle part of the plant. Fibre quality was similar in all treatments. However, damage ratings to individual bolls did differ between treatments. Bolls in the high insect density treatments received more damage than those in the low density treatments. As a result of this study, a tentative treatment threshold of 0.5 sucking insect/m2 is recommended in determinate Bollgard II cotton varieties grown in winter production areas.