What does Bt rice have to do with me?

Christie Birkle and Andrea Arriaga

What is bt rice?

• Bt refers to Bacillus thuringiensis which is a gram positive bacteria that lives in the soil.

• Bt has a toxin (Cry toxin) that is used in the fight against pests such as caterpillars, moths and butterflies.

• Since it is a natural pesticide, scientists decided to insert the gene that makes the Cry toxin into the plant genome.

What pests does the Bt toxin protect against?

• Stem borers and leaf folders (Chen et al.2006)

• Still have to spray for other pests not effected by the Cry toxin but spraying is much less.

*The pictures show the life cycle and damage leaf folders and stem borers cause to rice when not controlled. It is easy to see if they are not controlled, the whole harvest can easily be consumed by pests.

http://takingroots.in/ipm_rysb

It is already used as a pesticide?

• Yes… In the 1920s farmers recognized that the Bacillus thuringiensis spores and proteins could be used against pests eating their crops.

• Today they are used as insecticidal liquid sprays that go by the names of Dipel and Thuricide.

• Since they use Bt extracts, they are regarded as environmentally friendly that have little or no effect on humans, wildlife and pollinators.

• They are safe (and allowed) for use on organic farms.

How to make the Bt rice plant…

http://www.ctu.edu

How is the Cry toxin effective?• When bacteria spore due to unfavorable conditions as a survival tactic

they produce crystal proteins called Delta endotoxins that have insecticidal properties against insects.

• When insects ingest the toxin crystals, the alkaline pH of their gut interacts with the crystals making them soluble, allowing the protein to become active in the gut.

What does the active protein do?

• Once the protein is in its active form it will be absorbed by the cells lining the gut and form a pore.

• This will cause the cell to burst.

• When enough cells burst, the insect will die. Formation of a pore results in the unregulated influx of

fluid, causing cell lysis.

What are the benefits of using Bt rice?

• Its already used as an organic pesticide.• With the increasing resistance of pesticides,

genetically modified foods might be the only option.• Decreases pesticide use.• It costs about the same to plant both Bt and non-Bt

rice.• No harm to water living creatures that live in rice

fields.• Its ecofriendly!

How much pesticides are really used?

The market price of Bt cotton seed was more than US$ 4.85/kg in 1999. Because some farmers in the sample villages were contractors of Bt cotton seed reproduction, and some farmers saved seed or exchange seed after Bt cotton was adopted in the villages, on the average, farmers spent only US$ 1.77/kg on Bt cotton seed and US$ 0.78/kg on non-Bt cotton seed.

-This graph represents pesticide use in China, while the pesticide use in the Philippines is less, pesticide use for non-Bt varieties is still high.-The study by Huang and colleagues also said that Bt varieties seemed to promote the reduction of pesticide use.-Slow degrading pesticides also remain on the plants longer and led to poisonings when they were eaten.-Pesticide inhalation also causes poisonings and long term health problems.*This study was a study on Bt cotton in China in 1999 (Huang et al. 2003).

How much do Bt seeds cost compared to non-Bt? Bt Non-Bt

33B GK-12 GK-321 other

seed cost (US $) 66 44 69 69 63

pesticide used (kg/ha) 10.5 15 4.4 18.6 60.7

pesticide cost (US $) 30 41 16 40 178

fertilizer cost (US $) 1306 1089 2134 997 988

The table describes the total observations of 382 because some of the 282 households planted more than one variety. The sample distributions are 178 for SSB, 77 for GK-12, 42 for GK-321, 40 for other Bt, and 45 for non-Bt (Huang et al. 2003).

It is interesting to note that while seed price is the same and pesticide use is lower, the use of fertilizer is a little more.

*Note: these are Bt cotton seed prices studied by Huang and associates in 2003. The study says that rice pesticide use is lower.

Eco-friendly how?A study looking at the local rice fields showed that even the predators that ate the stem borers and leaf folders were not affected by the Cry toxin (Chen et al. 2003).There is no run off from spraying pesticides because the Cry toxin is inside the skin of the plant.The use of the Bt rice varieties also discouraged spraying later on in the year of pests that are not effected by the Cry toxin such as spiders, mites and bollworm (Huang et al. 2003).Since farmers are not mixing the highly toxic pesticide chemicals themselves the risk of poisoning is much lower.

Protect non-stem borers and leaf folders by supporting the cultivation of Bt rice and reduce pesticide use. Thank you for your time and happy planting!

References:Huang, J.; Hu, R.; Pray, C.; Qiao, F. and S. Rozelle.(2003) Biotechnology as an alternative to chemical pesticides: a case study of Bt cotton in China. Agricultural Economics 29 :55–67.

Chen, M.; Ye, G-Y.; Liu, Z-C.; Fang, Q; Hu, C.; Peng, H-F. and A.M. Shelton (2009). Analysis of Cry1ab toxin bioaccumulation in a food chain of Bt rice, an herbivore and predator. Ecotoxicology 18: 230-238.