Submitted to: Subtropical Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2011
Publication Date: 12/23/2011
Citation: Legaspi, J.C., Simmons, A.M., Legaspi, Jr., B.C. 2011. Evaluating mustard as a potential companion crop for collards to control the silverleaf whitefly, Bemisia argentifolii (Hemiptera:Aleyrodidae): outdoor and olfactometer experiments. Subtropical Plant Science. 63:36-44.
Interpretive Summary: “Push-pull” agriculture is the use of companion crops that repel an insect pest (“pushing” them away), together with attractive trap plants to “pull” them away from an economic crop. To develop a push-pull cropping design for the silverleaf whitefly, Scientists the USDA-ARS, Center for Medical Agricultural and Veterinary Entomology, Gainesville, Florida, first evaluated three varieties of mustard (giant red, tender green and ragged leaf) as potential repellent crops to be planted with collards. The numbers of whitefly landings through time did not show evidence that whiteflies initially preferred the collard crop, nor that did they avoid the mustard. Higher total numbers of whitefly landings were found on collards compared to any of the mustard varieties. Whitefly landings were also higher in the collards-only block, compared to collards that were paired with a mustard variety. Higher numbers of eggs were laid on the collards compared to any of the mustard varieties. However, there was no evidence that planting a companion mustard crop reduced numbers of eggs laid on collards. Laboratory studies showed weak attraction of adult whitefly females towards collards, versus a clean air control. A higher number of adult females selected the clean air control versus giant red mustard, but the result was not statistically significant. When presented with choices of collards versus giant red mustard, most whiteflies tested indicated “no decision”. Further research needs to be done in identifying repellent crops or products against whiteflies, and in the effects of plant odors on beneficial insects.
Technical Abstract: Three varieties of mustard (giant red mustard, tender green mustard and ragged leaf mustard) were evaluated as possible repellent companion crops for collards against the silverleaf whitefly, Bemisia argentifolii in outdoor potted experiments and through laboratory studies using a Y-tube olfactometer. The outdoor potted experiments showed higher numbers of whitefly landings on collards than on any of the mustards. When collards pots were grouped together with mustards as companion crops, whitefly landings were also lower than those of collards presented as monocultures. However, analyses of landings with time showed no initial preference for collards, nor avoidance of giant red mustard. Furthermore, analysis of egg counts showed strong ovipositional preference for collards compared to any of the mustards. However, numbers of eggs laid did not differ significantly among the crop combinations, suggesting that companion cropping with any mustard variety tested conferred no deterrence against oviposition by the whitefly. The olfactometer studies showed weak attraction of adult whitefly females towards collards, versus a clean air control. A higher number of adult females selected the clean air control versus giant red mustard, but the result was not statistically significant. When presented with choices of collards versus giant red mustard, most whiteflies tested indicated “no decision”. During the course of these experiments, we observed that some test insects attempted to retreat away from the air sources. Movement away from a volatile source may be construed as “repellency”. When an individual was observed to move 7 cm away from the air sources, the case was removed from the “no decision” category for re-analysis. The re-analyzed data again showed no significant attraction to collards, but provided some evidence of repellency away from mustard volatiles. We discuss difficulties in the use of the Y-tube olfactometers to study repellency.