Insect pests are the major challenge in agriculture apart from breeding of plants. Insect pests feed on plant parts like leaves, stems and flowers. This makes plants easily susceptible to plant diseases. Sometimes insects also act as vectors for disease causing pathogens like viruses etc.
Plants have their own defense system against insect pests. Insect pest resistance refers to the plants that are able to resist insect pest attack by releasing toxic substances that are harmful for insect pests. When the natural defensive system fails to resist, plants are genetically engineered by artificial means to produce resistance in them.
Insect resistant plant
It can be defined in many ways. In a broad sense, it can be defined: “A plant being relatively less damaged as the result of heritable resistant qualities than plant without qualities”
In practical agricultural aspect, it can be defined: “A crop with resistant properties yields more than a susceptible crop in the same insect pest attacking conditions.”
Transgenic crop of insect pest
An approach in the field of advanced agriculture through which the genome of plants is altered by introducing one or more desirable genes by using genetic engineering. Such plants are called transgenic crops. If resistant genes are introduced then plants are called transgenic insect pests.
Some transgenic crop varieties of insect pest are Pusa Gaurav (A variety of Brassica that has resistance to aphids), Pusa Seam 2 and Pusa Seam 3 (varieties of flat bean that have resistance to jassids, aphids and fruit borers), Pusa seven and Pusa A-4 (varieties of okra have resistance to shoot and fruit borers).
Mechanism of Host Plant resistance
The concept of mechanism of host plant resistance was given by R.H Painter (1951) who grouped it into three main categories:
- Non-preference or Antixenosis
- Non-preference or Antixenosis: –
The term “Non – Preference” refers to characteristics of the host plant which make it unattractive to insects for feed, shelter or oviposition This term was introduced by Kogan and Orthman (1978).
Insects do not choose some plants for shelter or oviposition due to the presence of undesirable characteristics like texture, hairiness, taste and flavors. Such plants undergo less damage by pest and this phenomenon is called Non- Preference or Antixenosis.
E.g., Wheat and cotton plants have hairy leaves that prevent jassids and leave beetles from eating them.
Solid stems in wheat are not preferred by the stem sawfly.
Bollworms are not attracted to smooth leaves and nectar-less cotton varieties.
- Antibiosis: –
There is an adverse effect on insect pests due to the presence of some toxic substances or absence of required nutritional compounds in the host plant. This process is called antibiosis. Such plants do not suffer as much damage as normal plants. The effect on insects may be reduced fecundity, decrease size and increased mortality etc.
E.gThe most classical example is DIMBO (2,4 Dihydroxy-7-methoxy-1,4 benzoxazin-3) content in maize which impart chemical defense against European corn borer Ostrinia nubilalis.
Certain plants like maize have high aspartic acid, low nitrogen and low sugar content that make them undesirable for stem borers.
- Tolerance: –
Some plants are said to be tolerant of a particular pest because of their ability to withstand the damage caused by insect pest by producing a greater number of tillers, roots or leaves in place of damage to plant parts. E.g., Early attack of sorghum shoots flies on the main stem of sorghum induced production of few synchronous tillers that grow rapidly and survive to produce harvestable ear heads.
Developing resistance in plants to insect pests has now great importance in entomology and agriculture. Plant resistance to insect pests has advantages over other direct control tactics. It should be encouraged for betterment of future modern agriculture.
Rimsha Awais B.Sc (Hons.) Agriculture Entomology Department of Entomology, University of the Punjab, Lahore