By Dr Sohail Ahmed and Abid Hussain
October 17 2005: TERMITES (Isoptera) are a group of insects consisting of 2,500 species of which 300 are considered as pests. The most troublesome are the fungus-growing of family termitidae. They feed on dead organic material such as crop residues, mulches and soil organic matter (humus).
Termites attack annual and perennial crops, especially in semi-arid and sub-humid tropics causing significant yield losses. Damage is greater in rain-fed than the irrigated crops during dry periods or droughts, in lowland, and in plants under stress (lack of moisture, disease or physical damage). Exotic crops are more susceptible to attacks.
Termites are farmer?s old age enemies. They feed on cellulose material. Intensive cropping for long periods reduces soil fertility and structure making the crop susceptible to termite attack.
Sugarcane is a tall tropical perennial plant of the genus Saccharum, a member of the grass family Gramineae. There are three species of the genus that are cultivated for commercial production of sugar of which S. officinaum is the most widely used species, and has probably been cultivated in Asia from the prehistoric times. It is attacked by termites along with other crops like maize, wheat etc.
During Second World War a weapon of pest destruction came on the scene which also started a war against insect pests. This was the emergence of epoch-making chemical group (organochlirine) which opened new horizons in insect control. People inverted gallons of aldrin, chlordane lindance heptachlor and the DDT for termite management.
Synthetic chemicals such as chlorpyrifos thiodan and bifenthrin are now used in place of the above chemicals. The adverse effects of synthetic insecticides i.e., two or three application in soil for termite control results in contamination of underground water and elimination of soil fauna.
Sustainable agriculture in the 21st century will rely heavily on alternatives interventions for pest management that are environmentally friendly and reduce the amount of human contact with chemical pesticides.
Some 700 species of entomopathogenic fungi have been reported but only 10 are currently developed for insect control. Some fungi mainly from Entomophthorales are insect pathogens and are effective in prolonged dampness. Over-wintering and soil inhabiting insect life stages are most susceptible.
By keeping in mind the hazards of synthetic pesticides, work on alternate strategies is in progress by the Termite Management Laboratory at the University of Agriculture, Faisalabad.
Among these, one is use of entomopathogenic fungi (Metarhizium anisopliae) against termite workers and alates. These are usually safe for humans and other non-target organisms. Based on required toxicity tests no risks to humans are expected from the use of products containing M. anisopliae. The fungus does not cause adverse effects in mammals and cannot grow at mammalian temperatures. As a precaution, people who apply termiticides are required to wear protective clothing etc.
Previous studies show that Metarhizium anisopliae is not harmful to earthworms or to such beneficial insects as ladybird beetles; green lacewings, parasitic wasps, honey bee larvae and honey bee adults.
The casual agent of green muscardine disease, M. anisoplae, is a naturally occurring pathogen which infects 200 species of insects including termites. It is investigated for the control of a number of economically important insects, such as the sugarcane beetles, carpenter ants, rice borers and termites.
Termites are highly social insects and engage in a variety of activities that necessitate frequent direct physical contact with other colony members. Trophallaxis (the exchange of regurgitated food), proctodeal trophallaxis (consumption of anal excretions) and grooming are regular necessary colony functions.
It is through grooming behaviour that the infective propagules of M. anisoplae can be transferred from one individual to another.
To create a high level of infection (an epizootic), a percentage of the colony is removed from the site of infestation, dusted with conidia and released back in the colony. As these conidia-carrying termites, or vectors (since they are mobile carriers for the fungus), encounter other colony members, they are groomed and the conidia are transferred so by this technique hundreds of termites are killed with only one millilitre of spore suspension.
There is a disadvantage that the fungal lifecycle may be particularly sensitive and dependent on humidity, moisture and free water, particularly during the stages of germination, penetration of the cuticle prior to growth, and hyphal reemergence and sporulation after the death of the insect. However, M. anisoplae fungus can survive 35-40C, which is a usual temperature in the crops? micro-environments. If humidity is the problem in arid areas or deserts, special type of chemicals can be used in combination with fungi to provide a good control.
Termite baits utilizing attractant and toxicant mixtures are sufficient to kill termites without creating bait shyness. There is a need for enhancing the effectiveness of entomopathogenic (capable of causing insect disease) fungal products and methods.
The foregoing discussion pertains to species of termites not common in Pakistan, thus there is need to study the in-field application of fungi.