*2.1. Transgenic Plants Expressing Biocide Polypeptides and Plant Defense*

Hunger continues to afflict mainly the poorer countries around the world. In 2016, 10.7% of the world population were chronically undernourished (www.worldhunger.org). According to data provided by the World Bank (www.databank.worldbank.org), over the last 15 years, the word population has increased with an annual growth rate of ~1% (1.075 in 2019), from 6.59 (2006) to 7.67 (2019) billions inhabitants. With the increase in life expectancy, from 69.2 (2006) to 72.5 (2018) years, particularly in the richer countries, even considering a decrease of growth rate, estimates are that the world population could reach 9.7 billion (www.population.un.org) in 2050. By then, food demand will be 60% higher (www.webforum.org). As agricultural land is finite (it increased only from 47.18 in 2006 to 48.43 in 2016 millions square kilometers according to the World Bank), and is expected to shrink due to urbanization, climate change and soil degradation, increases in food production will require an even more efficient agriculture. The output of agriculture is hampered, however, by losses in the field or after harvesting, by a variety of insect pests, nematodes, fungi and diseases induced by bacteria or viruses [13,14]. Herbivores alone feeding on foliage, sap and root can decrease more than 20% of net plant productivity and food losses to insects are expected to even grow in a scenario of global warming [15].

To efficiently control insect pests in agriculture, combining different strategies is frequently required, including the use of resistant crop varieties. When there is no natural plant genotypes genetically resistant to insect pests, development of genetically modified (GM) resistant plants is an option. A milestone in the development of insect-resistant crops was established in the late 1980′ s, by genetically engineering a tobacco plant to express an entomotoxic protein from the bacterium *Bacillus thuringiensis*(Bt) [16,17]. In 2018, the list of genetically modified plants that were commercialized had 26 species, either tolerant to herbicides or with increased resistance to insects (most expressing *Bt* toxins), grown or imported in 75 countries (www.gmoanswers.com). *Bt* toxins (or Cry proteins) have some restrictions, such as the low toxicity against sap-sucking insects [18,19]. Moreover, an increasing level of resistance of insects against Cry insecticidal proteins has been reported [20]. Fortunately, there is a number of plant entomotoxic proteins that can be used instead or in synergy with the *Bt* technology to control insect pests in new generations of transgenic plants yet to be developed [21].
