November 20, 2006	Monday	Shawwal 27, 1427

IN Pakistan like rest of the world, herbicides, insecticides, fungicides and rodenticides are being increasingly used in agriculture. Their use has created serious ecological problems. These chemicals degrade the quality of air, water, soil and biota.

On gaining access to the food chain, some of these toxicants are not excreted from the consumers’ bodies. As such, these get concentrated in the bodies of consumers at the top of trophic hierarchy. These toxicants cause a variety of ailments and some time death in man and animals. Pest problems aggravates when natural predators are eliminated by pesticides. The chemical control methods protect crops from being damaged by pests, they seriously deplete biodiversity. While in terms of depletion of biodiversity, the FAO estimates that in the next 10 years, about 90 per cent of the existing genetic biodiversity within main crops is at stake.

In recent years, the rate of global biotic impoverishment has accelerated due to causes triggered by man. If this trend continues then by 2050, the world might witness a loss of up to one quarter of the species. The scenario in Pakistan would be graver as this will have an adverse impact on farm production. The combined effect of population explosion, water scarcity, and environmental pollution will be clossal. The dangers of global warming due to green house effect would add to it.

‘Mother Earth’ is unique as resilience and adaptability has been its hallmark. Man’s perseverance and innovations have been the secrets of his success in solving problems. After losing chemical war against pests, he now realizes the benefits of being in conformity with the Nature.

Spiders (phylum arthropoda; sub-phylum chelicerate, class arachnida; order araneae) fall comes under natural control factors. They form a significant component of food web in both the natural and man-made ecosystems.

Until now 110 families, 3,618 genera and 39,112 species of spiders have been described. As many as 50,000 individuals of spiders per acre have been recorded in cultivations. They form one of the most ubiquitous groups of predaceous organisms in the animal kingdom. They feed almost exclusively on insects.

Spiders not only prey upon larvae and adults but also cause indirect mortality in them through disturbance. Spiders kill for more pests than commercial insecticides. According to one estimate, spiders devour enough bugs worldwide in a single day to out-weight the entire human population. A spider will kill as much as 50 times the number of prey it actually consumes.

In each ecosystem, the impact of spiders is two ways. These are predatory pressure of the whole group of spiders on the entomocoenosis, and the pressure of particular spider species on some species of insects. Under crop conditions, spiders are important enemies of aphids, mites, and lepidotera larvae and eggs. Spiders along with other general predators, largely account for maintaining biocoenotic stability in ecosystems.

Spiders can be used as the natural enemies of insect pests in orchards. Spiders have been released in rice fields in the People’s Republic of China as biological control agents of rice pests. The potential of spiders as natural control agents of arthropod pests aroused interest in learning more about them.

For employing spiders in the Integrated Pest Management (IPM), we need to know more about their taxonomy i.e., diversity and ecology in the local agro-ecosystems and biology. Studies on key species of a community for knowing about size, sex ratio and abundance may provide useful ecological data and facilitate in assessing the predatory potentials. Spiders in Pakistan have been only sparingly studied and have never been tested for combating insect pests in the agro-ecosystems.

The author surveyed the foliage and ground spider fauna of Punjab under partial sponsorship of the University Grants Commission. Spiders were collected from 43 locations in 21 districts of Punjab and also from one location in Federal Territory, Islamabad from 1996 through 1998.The Districts sampled for spiders were Faisalabad, T.T. Singh, Jhang, Sheikhupura, Lahore, Gujranwala, Sialkot,

Jehlum, Rawalpindi, Chakwal, Sargodha, Okara, Sahiwal, Khanewal, Multan, Muzaffar Garh, Bahawalnagar, D.G. Khan, Vehari, Leiah and Rahim Yar Khan.

As many as 14,743 spiders were captured. All these were identified as belonging to 21 families, 58 genera and 157 species. Out of these, 80 species have never been recorded from this area. Among these 32 species were cognized as new to the science. It is believed that there are still a number of spider species from these areas which have not yet been explored. Diversity and abundance of some was specific to different climatic zones and different crops like maize, fodder, rice, sugarcane, cotton, orchards etc.

Spiders are diverse in size, feeding and hunting strategies, and time of activity. Most species are reported as having important role in regulating insect populations injurious to various types of plants in orchards and crops.

Spiders of family micryphantidae feed on injurious insects of tobacco plants. These Linyphiid spiders consume a wide range of insect species. The prey preference varies with space and time depending upon density of particular species at a particular time and place.

Almost all the species of family araneidae (orb-weavers) construct orb-webs on grass and are not ground dwellers. They devour all sorts of arthropods which entangle in their webs. They also cast webs over nymphs to disperse from paddy fields, thus reducing the damage.

The lycosids (wolf-spiders) occupy a variety of habitats from sea-shore to the high mountains. Almost all are ground dwellers. They feed on a variety of insects like diptera, lepidotera, dictyoptera, hymenoptera, coleoptera, collembola, dermoptera etc. They can be effectively used in various crops.

The clubionids or sac-spiders run over the ground under stones or grassy lands as well as rocky ground under the stones, folded blades of grass and under loose bark of trees or leaf-litter. They are useful predators of many harmful insects of crops.

For example thomisidae are effective predators in cotton field. They are found on flowers and feed on insects visiting flowers. They are effective predators in cotton fields.

Species of family philodromidae are effective predators of red and brown mites as well as lepidoptera larvae in peach, apple and banana orchards and in cotton fields.

Spiders of the family oxyopidae are predators of harmful insect orders like diptera, (mosquites and flies), wasps heteroptera, homoptera, coleopotera, butterflies , bugs, neuroptera and odonata in cotton fields.

Spiders of the family salticidae have a wide range of distribution and can be employed in various crops for effective insect control.

Workers in China and Japan have used spiders for control of insects by colonizing them in fields. Once spiders are introduced in the field, it is important to limit their movement out of the area.

Spiders migration seems to be related to the following factors (a) unfavourable thermal environments, (b) low prey availability and (c) disturbance. They also need shelter after foraging bouts. Jones (1981) reported that the Chinese used straw bundles to provide shelter for spiders. These bundles were initially laid down in areas where spiders were numerous and then transported from field to field as needed to implement control.

Practical application of spiders in croplands and orchards of Pakistan can save billions in foreign exchange, prevent drastic ecological changes and mortality and diseases caused by insecticides.