To the Rescue: Insects in Sustainable Agriculture

by Ada Bielawski

In 1798, Thomas Malthus published his Essay on the Principle of Population and described the limits of human population growth: the population will continue to grow exponentially while the Earth’s resources are able to sustain the increasing food production needed to feed this population. He concluded that, as the population approaches 8 billion, the poorest will suffer the most from limited resources.¹ Currently, over 14% of the world’s population is underfed, and the growing population is expected to reach 9 billion less than 50 years from now.² Thus, there is a dire need to increase crop yields to feed the growing population. This must be done while also mitigating the effects of agricultural production on the Earth’s limited resources. Therefore, instead of relying on destructive tools—such as deforestation to create more farmland—increasing crop yields through sustainable agriculture is the key to a better future.²

We can increase crop yields and decrease environmental stress through IPM. Integrated Pest Management (IPM) is an ecological approach to pest defense that aims to minimize the use of chemical pesticides and maximize environmental and consumer safety. Farmers utilizing IPM use their knowledge of pests and how they interact with their habitat to eradicate them most efficiently.³ IPM is more sustainable than pesticides but can be less effective, so farmers are reluctant to implement IPM measures that actually do work.

ANT IPM

Oecophylla smaragdina—commonly known as Weaver ants—have been used as an anti-pest crop protector since 304 AD, when Chinese markets sold ants to protect citrus fruit.^5,6 Today, after decades of chemical pesticide use, ant IPM has reemerged as a sustainable option for crop defense.^4,5,6 Ants are a great tool for many reasons: (1) they are a natural, accessible resource, responsible for 33% of insect biomass on Earth; (2) they can quickly and efficiently build populations at a nest site due to behavioral habits such as path-making, worker recruitment, and pheromone attraction; and (3) they encompass a range of roles and behaviors that make them capable of attacking a variety of pests at many stages of their life cycle.^4,5 With these characteristics, ants form a mutualistic relationship with their host plant: the plant attracts their food source and provides a home, while the ants attack the pests that would cause the plant harm.⁷

Ants do the work of chemical pesticides with increased safety and damage control.^4,6,8 There have been 17 studies conducted that evaluate the success of ant pest management for nine crops in a total of eight countries. Of these studies, 94.1%showed a decrease in pest number and damage done by the pests. One of these studies, done on cashew trees in Tanzania, showed that the damage found on cashew trees with ants was reduced by 81% from the damage on control trees, and nut damage was reduced by 82%. Furthermore, 92.3% of reports studying crop yields favored ant IPM over chemical pesticides. Of the studies that compared the results of ant pest control to chemical-based pest control, 77.8% favored ants.⁴

Moreover, ants as pest control can cost less than their chemical counterparts. In Northern Australia, researchers studied the cost and crop yields of cashew crops between plants with chemical pesticides and plants with ant IPM treatment. The weaver ants showed a 57% reduction in cost over a period of 4 years, and a crop yield 1.5 times the size of the one for chemical pesticides. This resulted in savings of over $1500/hectare/year, which led to a 71% increase in revenue for farmers.^4,8 These results prove that ants have the potential to be not only a more sustainable tool for agriculture, but also a more cost-effective method of pest management.

Ant IPM has demonstrated promise for the future of sustainable agriculture. Future research should: (1) focus on identifying all the crops that could benefit from ant IPM; and (2) study more of the 13,000 ant species, whose unique attributes could target a wider variety of crops.^4,6

MOTH IPM

Plutella xylostella, the diamondback moth, is a pest that targets cruciferous crops, such as cabbage.^9,10,14 The larvae feed on the green sprouts and reduce not only crop yield, but also crop quality.¹⁰ To protect against these moths in the past, scientists created a genetically modified (GM) crop that produced a bacterium—Bacillus thuringiensis (Bt)—which was toxic to the pest it targeted^9,11,12 but safe for other insects, animals, and humans to consume.¹³ This was an effective method for controlling diamondback moth populations until the pests developed resistance to the bacterium.⁹

Scientists from Oxitec set out to solve this perpetual resistance problem by inserting a transgene into the diamondback moth genome.^9,14 The transgene has three main components: (1) a tetracycline-repressible dominant female-specific lethal transgene: larvae are fed tetracycline while they mature, and then when released, female GM moths die due to insufficient levels of tetracycline in the wild, whereas males survive (this process also occurs with all the female progeny of the GM moths); (2) a susceptibility gene: this gene makes GM moths susceptible to Bt; and (3) a fluorescent tag: this allows scientists in the field to distinguish which moths have the transgene.⁹

In the Oxitec study, GM moths were released into a caged, wild-type moth population in high numbers every week. Researchers recorded the number of eggs collected, the number of dead females, and the proportion of the transgenic progeny to wild-type progeny. Wild-type females mated with the GM male moths, and all of the second-generation females died before they reached reproductive age. Since the number of females decreased in subsequent generations, the population became 100% transgenic in ~8 weeks, and then went extinct ~10 weeks from the initial release of GM moths. Thus, GM moths have the potential to not only reverse Bt resistance in their species, but also eliminate the use of Bt crops.⁹

IPM is the solution to a more sustainable means of food production while the Earth’s population continues to grow beyond the bounds of available resources. Weaver ants have proved to be efficient and cost-effective crop defenders, while new research utilizing GM technology on Diamondback moths has shown major promise in reducing targeted pest populations and their resistance to chemical pesticides. These two examples clearly illustrate the potential of IPM for pest management in the near future.

Ada Bielawski ‘18 is a sophomore in Mather House, concentrating in Integrative Biology.

Works Cited

1. Malthus, T.R. An Essay on the Principle of Population; J. Johnson: London, 1798, 6-11.
2. Godfray, H.C.J. et al. Food Security: The Challenge of Feeding 9 Billion People. Science 2010, 327, 812-818.
3. U.S. Environmental Protection Agency. Integrated Pest Managemnet (IPM) Principles. http://www.epa.gov/pesticides/factsheets/ipm.htm (accessed Oct. 4, 2015).
4. Offenberg, J. Review: Ants as tools in sustainable agriculture. J. Appl. Ecol. 2015, 52, 1197-1205.
5. Van Mele, P. A historical review of research on the weaver ant Oecophylla in biological control. Agric. For. Entomol. 2008, 10, 13-22.
6. Pennisi, E. Tiny ant takes on pesticide industry. Science [Online], Aug. 30, 2015. http://news.sciencemag.org/plants-animals/2015/08/tiny-ant-takes-pesticide-industry (accessed Oct. 9, 2015).
7. Offenberg, J. et al. Observations on the Ecology of Weaver Ants (Oecophylla smaragdina Fabricius) in a Thai Mangrove Ecosystem and Their Effect on Herbivory of Rhizophora mucronata Lam. Biotropica. 2004, 3, 344-351.
8. Peng, R.K., et al. Implementing ant technology in commercial cashew plantations. Australian Government Rural Industries Research and Development Corporation. 2004, 1-72.
9. Harvey-Samuel, T. et al. Pest control and resistance management through release of insects carrying a male-selecting transgene. BMC Biol. 2015, 13, 49.
10. The Asian Vegetable Research and Development Center Diamondback Moth Management. 1986, x. http://pdf.usaid.gov/pdf_docs/pnaav729. pdf (accessed Oct. 7, 2015).
11. University of California San Diego. What is Bt. http://www.bt.ucsd.edu/what_is_bt.html (accessed Oct. 4, 2015).
12. University of California San Diego. How does Bt Work.  http://www.bt.ucsd.edu/how_bt_work.html (accessed Oct. 4, 2015).
13. University of California San Diego. Bt Safety. http://www.bt.ucsd.edu/bt_safety.html (accessed Oct. 4, 2015).
14. Oxitec. Press Release- Oxitec announces breakthrough in GM insect technology for agricultural pest control. http://www.oxitec.com/press-release-oxitec-announces-breakthrough-in-gm-insect-technology-for-agricultural-pest-control/ (accessed Oct. 4, 2015).