Submitted to: Journal of Sugarbeet Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/26/2003
Publication Date: 10/1/2003
Citation: Smigocki, A.C., Campbell, L.G., Wozniak, C.A. 2003. Leaf extracts from cytokinin-overproducing transgenic plants kill sugarbeet root maggot (tetanops myopaeformis) larvae. Journal of Sugarbeet Research. 40(4):1-11. Interpretive Summary: Disease and pest problems are responsible for decreases in production of sugar from sugarbeet. One of the most devastating insect pests of sugarbeet is the sugarbeet root maggot that currently is found in half of all the sugarbeet fields. Chemical insecticides are the only available measure for control of the maggot and a strong impetus exists for development of alternative control measures. We tested the effect of insecticidal compounds found in genetically modified tobacco plants on the sugarbeet root maggot larvae. Exposure of the larvae to these compounds induced an almost immediate, repetitive twitching and thrashing movement that was not detected in extracts prepared from unmodified plants. The twitching and thrashing response was followed by death. After 5 days, most (92%) of the larvae exposed to the insecticidal compounds were dead and most of the ones that were still alive were twitching. These results suggest that plant-derived insecticidal compounds can be exploited for development of effective means to control the sugarbeet root maggot. This information will be used by scientists to increase our knowledge of the mechanisms controlling plant responses to insects and lead to environmentally safe approaches for reducing the use of harmful pesticides.
Technical Abstract: The sugarbeet root maggot (SBRM), Tetanops myopaeformis, is the major insect pest of sugarbeet in the central and western United States and Canada and is capable of inflicting losses ranging from l0 to l00%. Currently, chemical insecticides are the only available measure for control of the maggot and a strong impetus exists for development of alternative control measures. We tested the effect of insecticidal leaf extracts of N. plumbaginifolia plants transformed with the cytokinin biosynthesis gene ipt on the sugarabeet root maggot larvae. Exposure of first instars to a 0.l or l% suspension of the compounds in surface extracts induced an almost immediate, repetitive twitching and thrashing movement that was not detected in the control extracts. After 24 hr, 68% of the larvae in the transgenic extract were twitching as compared to none in the control extract. In general, the twitching and thrashing was the first response of the larvae to the transgenic extract that was followed by death. After 4 days, more than two thirds (41 out of 60) of the larvae treated with the 1% transgenic suspension were dead and, of the remaining larvae, 62% (12 out of 19 that were still alive) were twitching. After 5 days, 92% (55 of 60) of the larvae were dead and 2 of the remaining 5 were twitching. A ten-fold dilution of the surface extract suspension (0.l%) killed more than 80% of the larvae at 5 days and, of those that were still alive, 40% were twitching. In the 1% control extract prepared from untransformed plants, no twitching was observed for up to 3 days, at which point only 5% (2 out of 40) of the larvae died and only 4% of the remaining larvae were twitching. These results suggest that cytokinin mediated insect resistance can potentially be exploited for development of effective control strategies for the sugarbeet root maggot.