The rapid adoption of genetically engineered (GE) plants that express insecticidal Cry proteins derived from Bacillus thuringiensis (Bt) has raised concerns about their potential impact on non-target organisms. This includes the possibility that non-target herbivores develop into pests. Although studies have now reported increased populations of non-target herbivores in Bt cotton, the underlying mechanisms are not fully understood. We propose that lack of herbivore-induced secondary metabolites in Bt cotton represents a mechanism that benefits non-target herbivores. We show that, because of effective suppression of Bt-sensitive lepidopteran herbivores, Bt cotton contains reduced levels of induced terpenoids. We also show that changes in the overall level of these defensive secondary metabolites are associated with improved performance of a Bt-insensitive herbivore, the cotton aphid, under glasshouse conditions. These effects, however, were not as clearly evident under field conditions as aphid populations were not correlated with the amount of terpenoids measured in the plants. Nevertheless, increased aphid numbers were visible in Bt cotton compared with non-Bt cotton on some sampling dates. Identification of this mechanism increases our understanding of how insect-resistant crops impact herbivore communities and helps underpin the sustainable use of GE varieties.
Aphids
“Aphids” contains two sheets one given the aphid population of all plants used in the experiment, while the second contains the average hind tibia length in mm of aphids from each plant
Heliothis and Plant Damage
“Heliothis and Plant Damage” contains two sheets, one given the survivial and weight in mg of H. virescens on Bt an non-Bt cotton. The second the leaf damage in cm2 caused by H. virescens on both plant types. NOTE: The lower number of data entries in the plant damage sheet is caused by loss of raw data due to a camera malfunction.
Gossypol content in response to H. virescens
“Gossypol content in response to H. virescens “ gives the terpenoid concentrations of oldest and youngest leaf of Bt and non-Bt cotton that were uninfested or infested with H. virescens for one week. All data is ng/terpenoids per mg dry weight leaf.
NOTE: Terpenoid data from our field study is included in the Field Experiment data sheets to ease comparison of data.
Gossypol content in response to Jasmonic Acid
“Gossypol content in response to Jasmonic Acid” gives the terpenoid concentrations of oldest and youngest leaf of Bt and non-Bt cotton that were untreated or treated with Jasmonic acid one week before collecting the leaf. All data is ng/terpenoids per mg dry weight leaf.
NOTE: Terpenoid data from our field study is included in the “Field Experiment” folder to ease comparison of data.
Summary_Plants infested with Spodoptera
“Summary_Plants infested with Spodoptera” contains the data of the field experiment plants there were artifically infested with S. exigua. The File contain three sheets detailing the aphid population per plant and sample date, the damage of each plant per screening data and the final terpenoid concentration of each plant at the end of the experiment.
NOTE: Plant identifiers are consistent for each data set. Missing entries are caused by problems during data collection, e.g. corrupted or blurred jpeg files during plant damage assessment.
Summary_Plants naturally infested
“Summary_Plants naturally infested” contains the data of the field experiment plants that were only exposed to natural infestation.
Both files contain three sheets detailing the aphid population per plant and sample date, the damage of each plant per screening data and the final terpenoid concentration of each plant at the end of the experiment.
NOTE: Plant identifiers are consistent for each data set. Missing entries are caused by problems during data collection, e.g. corrupted or blurred jpeg files during plant damage assessment.