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Potential Insect Deterrence in a Tri-Species Cotton Hybrid
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Currently, insecticide applications and Bt cotton are the primary means for managing insect pests in cotton, but many of these pests have developed resistance to pesticides. Because of resistance, host plant resistance may be a viable solution to prevent significant yield losses. Tri-species cotton hybrids consisting of either Gossypium hirsutum L., G. arboreum, and G. armouranium, or G. hirsutum, G. arboreum, and G. turneri have been reported to contain β-caryophyllene derivatives (12-hydroxy-β-caryophyllene and hydroxy-β-caryophyllene acetate) and demonstrated resistance to nematodes, drought, and heat. Yet, there is a lack of evidence whether these hybrids affect cotton insect pests. A series of field, greenhouse and laboratory experiments were conducted to assess the impact a tri-species cotton hybrid expressing β-caryophyllene, or its derivatives, β-caryophyllene acetate and alcohol, and β-caryophyllene alcohol, have on tobacco thrips, Frankliniella fusca (Hinds), western flower thrips, Frankliniella occidentalis (Pergande), cotton aphid, Aphis gossypii Glover, fall armyworm, Spodoptera frugiperda (J.E. Smith), and bollworm, Helicoverpa zea (Boddie). Gas chromatography-mass spectrometry (GC/MS) was initially used to confirm the presence of β-caryophyllene and its derivatives in individual tri-species cotton hybrid plants. The impact of the tri-species cotton hybrid plants on preventing thrips injury in field trials was inconclusive. At the 1-2 true leaf stage, the tri-species hybrid plants expressing β-caryophyllene and its derivatives (c. acetate and alcohol and c. alcohol) did not differ from G. hirsutum or G. hirsutum seed treated with the insecticide imidacloprid (IST). At the 2-3 and 3-4 true leaf stages, differences among treatments in the frequency distribution of thrips injury ratings was more evident, and although slight, injury tended to be lower for the tri-species hybrid than for G. hirsutum and G. hirsutum (IST), particularly for the two β-caryophyllene derivatives in 2020. Although inconclusive in field trials, in a greenhouse choice test, the tri-species hybrid cotton had less colonization and fewer alate cotton aphids than G. hirsutum. Furthermore, in a cotton aphid reproduction study, intrinsic rate of increase, and finite rate of increase was lower for the tri-species hybrid plants expressing β-caryophyllene or its derivative c. alcohol relative to G. hirsutum. When fed leaf tissue, the tri-species cotton hybrid did not affect cotton bollworm larvae development, relative to G. hirsutum. However, fall armyworm larvae feeding upon the leaves of the tri-species cotton hybrid expressing c. alcohol, were smaller and did not mature as quickly as larvae feeding on G. hirsutum or the tri-species cotton hybrid expressing only β-caryophyllene, or the c. acetate and alcohol derivative. Results suggest that the tri-species cotton hybrid, especially those capable of expressing c. alcohol, negatively impacts, albeit minor, several insect pests of cotton.
Allison, Raven S (2021). Potential Insect Deterrence in a Tri-Species Cotton Hybrid. Master's thesis, Texas A&M University. Available electronically from