Abstract
Maize with enhanced β-carotene production was engineered to counteract pervasive vitamin A deficiency in developing countries. Second-generation biofortified crops are being developed with additional traits that confer pest resistance. These include crops that can produce Bacillus thuringiensis Berliner (Bt) insecticidal proteins. Currently, it is unknown whether β-carotene can confer fitness benefits through to insect pests, specifically through altering Ostrinia nubilalis foraging behaviour or development in the presence of Bt insecticidal toxin. Therefore the effects of dietary β-carotene plus Bt insecticidal protein on feeding behaviour, mortality, and physiology in early and late instars of O. nubilalis larvae were investigated. The results of two-choice experiments showed that irrespective of β-carotene presence, at day five 68%-90% of neonates and 69%-77% of fifth-instar larvae avoided diets with Cry1A protein. Over 65% of neonate larvae preferred to feed on diets with β-carotene alone compared to 39% of fifth-instar larvae. Higher mortality (65%-97%) in neonates fed diets supplemented with β-carotene alone and in combination with Bt protein was found, whereas <36% mortality was observed when fed diets without supplemented β-carotene or Bt protein. Diets with both β-carotene and Bt protein extended 25 days the larval developmental duration from neonate to fifth instar (compared to Bt diets) but did not impair larval or pupal weight. Juvenile hormone and 20-hydroxyecdysone regulate insect development and their levels were at least 3-fold higher in larvae fed diets with β-carotene for 3 days. Overall, these results suggest that the effects of β-carotene and Bt protein on O. nubilalis is dependent on larval developmental stage. This study is one of the first that provides insight on how the interaction of novel traits may modulate crop susceptibility to insect pests. This understanding will in turn inform the development of crop protection strategies with greater efficacy.
Highlights
Plant chemical composition, including primary and secondary metabolites, mediates plantinsect interactions
This study investigated whether β-carotene and Cry1A insecticidal protein interact to alter the behaviour, performance, and physiology of O. nubilalis larvae, a major pest of maize and target for Cry1A
The results of ELISA confirmed that diets with B. thuringiensis (Bt)-maize leaves had the target Bt concentration of 31.5 ± 6 μg/g fresh weight, which is similar to the concentration of Bt protein found in leaves and kernels of commercial Bt maize DKC6667Y and HC × Bt maize [17]
Summary
Plant chemical composition, including primary and secondary metabolites, mediates plantinsect interactions. Herbivorous insects selectively feed on plants that provide necessary nutrients to fuel growth, development, and reproduction [1]. Gustatory neurons housed within sensilla on mouthparts (e.g. mandibles, maxillae, and labial palps) aid insects in distinguishing between nutrients and non-nutrients in plants [2]. Stimulating or deterrent plant compounds influence insect feeding choices [3]. Biotic and abiotic factors drive spatio-temporal variation in plant chemistry [4] that affects insect performance and development [5]
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