Plants can be resistant or susceptible to insect attack. They can also be selected by breeders for these specific traits or they maybe genetically modified to increase their resistance to insect pests.
Plants defend themselves from insect attack by different means:
- Antibiosis – certain plant parts can adversely affect insect biology
- Antixenosis – some plant characteristics can deter insects
- Tolerance – plants can tolerate insect damage
- Sorghum – over 99% of grain sorghum in Australia has some level of Midge Resistance (MR) with most commercial hybrids rating from 4-6. The high level of adoption of MR cultivars and the elimination of low rated MR hybrids means that spraying for midge is now very rare with less than 5% of crops treated, in contrast to the mid 1990s when 30-40% of the crops were sprayed. The use of resistant hybrids also means that natural enemies are conserved.
- Chickpeas – deter most insects except Helicoverpa through high levels of malic acid in their leaves
- Narrow leaf lupins – some varieties are resistant to aphid feeding damage (Tanjil and Wonga) while others are susceptible (Yorrel and Tallerack)
- Canola – susceptible to insect attack owing to small colyledons and exposed growing tips. This susceptibility to insects has resulted in canola frequently being treated with prophylactic insecticides to avoid any potential damage.
- Pulses – have some vulnerability to insect attack as they have exposed growing tips but less so than canola as pulses have more robust and fleshy cotyledons
- Cereals – have growing tips that are concealed and hence can tolerate much higher levels of damage than pulses and canola.
Genetic engineering techniques have enabled specific genes – such as insecticidal toxins – to be inserted into the molecular structure of some crop plants. Examples of these are varieties of cotton and canola which contain the toxins of Bacillus thuringiensis (Bt).
Some cultivars of transgenic field peas in Western Australia are showing promising results with resistance to the pea weevil. However, further development of transgenic cultivars with insect pest resistance is less likely while effective and cheap chemical control remains available.
Host susceptibility characteristics are important when considering pest management options.
- Host plant resistance (University of Wisconsin-Madison)
- Plant Resistance to Insects: A Fundamental Component of IPM (University of Minnesota)
- Enhancing host plant resistance of Australian cotton varieties. The Australian Cottongrower, January-February 2002.