Relay intercropping to enhance abundance of insect predators of cotton aphid (Aphis gossypii Glover) in Texas cotton

Relay intercropping winter and spring strip crops with cotton was used to conserve and enhance the numbers of predators of the cotton aphid ( Aphis gossypii Glover) in 1992, 1993 and 1994 in northern Texas, USA. Numbers of aphids and aphid predators in cotton isolated from other crops were compared with numbers where canola, wheat, sorghum (strip intercrops) and cotton were planted adjacent to each other and overlapped temporally. Aphid and predator populations were also monitored in the intercrop. The intercrops acted as a reservoir for predators during the non-cotton season; these intercrops 'relayed' aphid predators from canola and wheat in the winter to sorghum in the spring and finally to cotton in the summer. Averaged over the three years ofthe study, predator numbers in the intercrops were highest in sorghum and lowest in wheat. In all years, canola had higher predator numbers than wheat, suggesting that it would be a better winter intercrop than wheat for enhancing predator numbers. Average aphid abundance was lower in relay intercropped cotton than in isolatedcotted each year. The three year average in relay intercropped cotton remained fewer than 193 aphids perleafon anyone sample date, butreached 490 aphids perleaf in isolated cotton. Seasonal abundance of aphid populations was bimodal in relay intercropped cotton, with peaks in early August and early September, while populations peaked only once in late August in isolated cotton. Average predator numbers were higher in relay intercropped cotton than in isolated cotton, and predators appeared in higher numbers earlierinthe summer in relay intercropped cotton than in isolated cotton. Results from this study suggest that where cotton is grown without insecticides, relay intercropping aids the early arrival and continuous population increase of predators in cotton, thereby reducing numbers and postponing the initial population increase of the cotton aphid.

Keywords:

• Intercropping
• Strip Crops
• Cotton Aphid
• Biological Control
• Insect Predators