Biological control is a method of controlling pests such as insects, mites, weeds, pink bollworm and plant diseases using other organisms.
It relies on parasitism predation, herbivory and other natural devices, but typically also involves an active human management role. It can be an important component of integrated pest management (IPM) programs.
Importance of cotton
After wheat cotton is a chief crop of Pakistan and it grown on largest area in Pakistan. Cotton is a main cash crop in our country. It is mostly developed for fiber, cotton lint, cloth, wool and garments because there are a large source of foreign exchange and accounts for 2.9% of GDP of Pakistan.
Their production is lower than many advanced countries. One of the main problem is low yield i.e. 20-30% is damage by insect pests and diseases. For the abundance of pests, dry and moist environment is favorable, particularly for American bollworm that produce significant losses.
Commonly used Parasitoids and predators for the control of pink bollworm
Order Hymenoptera involves 160 species and 43 Genera. Genera includes the Apanteles, Chelonus, Bracon, Brachymeria, and Elasntus. Between parasitic hymenoptera there are many species of possibly useful pink boll worm parastoids. Some are larval parasitized, egg parasitized and some have both egg and larval parastized, But the most useful parasitized are egg-larval parasitized, Chelonus spp.
- Apanteles sp. (Braconidae)
These are larval parasitoid. Apanteles larva feed and grow on its specific host and ultimately kill them. When they become mature, Apanteles larvae leave their host and individually spin cocoons in the shelter of leaf in which host are present.
- Brachymeria sp. (Chalcididae)
Brachymeria belongs to family Chalcididae and genus of parasitic wasps. More than 300 species are present in the word and all are larval parasites. These are black with narrow yellow markings, and chalcidid wasps and hind femora are large in size.
By the using of ovipositor the female start eggling inside the lepidopteran larvae. Mostly are parasitic but the few are hyperparasites and these damage the other larvae (such as Polistes erythrocephalus).
Predators are feeds on eggs of pink bollworm and also the larvae of first instar of pink bollworm. There are many groups of arthropods which naturally attack on pink bollworm, containing Coleoptera, Mites, Dermaptera, predaceous, Hemiptera and Neuroptera.
The egg stage is most susceptible to attack by predators because it is comparatively exposed when compared to larvae and pupae. Many predators have few morphological variation of the mouthparts and the legs it is necessary to enter into bolls for the feeding of larvae on pink bollworm. In Dermapteran Labidura riparia these attacks on all immature stages of pink bollworm including pupa.
However, the predator is not a dominant element in a predatory complex. Hemiptera are abundant in cotton fields, and at least five species in five genera of Hemiptera have been recovered from pink bollworm. Hemiptera seem to express the broadest range of attack, feeding on eggs, larvae, cocooned larvae and probably pupae.
Coleoptera are well represented with four species in four genera attacking pink bollworm. Most beetles focus on eggs and early instar larvae as prey. Chrysoperla carnea (Stephens) is the only neuropteran reported attacking pink bollworm.
Among the hundreds of beneficial species commonly devouring cotton pests are green and brown lacewings, pirate bugs, big-eyed bugs, assassin bugs, damsel bugs, spined soldier beetles, Staphylinid rove beetles, Carabid ground beetles, Collops beetles, lady beetles.
- Labidura riparia
Predators whose diet consists entirely of insects, or scavenged meat. They have a preference to Lepidoptera larvae and insect eggs, but will eat any available insect. Because of their flexible eating habits, they easily adapt to any habit as long as there are insect around. In absence of a ready food supply, they have been known to eat nymphs and eggs of their own species.
As nocturnal insects, earwigs only hunt after sunset, but feed primarily just after sunset occurs. Feeding habits of females depend more on their ovulatory cycle, and will go long periods of time without eating in preparation of egg laying.
Pink bollworms first detected from damaged bolls of cotton in India in 1843. Saunders first time called pink bollworms in 1843 as (deprassia gossypiella). Through the transport of cotton and cotton related products it spread all indo-pak.
Worldwide, pink bollworm has become economically the most destructive pest of cotton and has known to cause 2.8 to 61.9 per cent loss in seed cotton yield, 2.1 to 47.1 per cent loss in oil content and 10.7 to 59.2 per cent loss in normal opening of bolls
The pink bollworm is a major pest of cotton crop. The adult moth is small, tinny, gray with fringed type’s wings. The larva is, eight-legged caterpillar and dull white in colour with exposed pink banding along its dorsum. The larva length ranges in one half inch. The female moth start egg-ling in a bolls of cotton crops, and after the emergence of larvae from the eggs, they cause damage by feeding.
Need for biological control
In Pakistan pink bollworm is mostly controlled by the use of insecticides and Bt cotton. But with the passage of time pink bollworm is developing resistance against insecticides and Bt cotton.
In Pakistan pink bollworm infest the cotton crop which decrease the yield in every season. These also damage the quality of cotton seed and fibre quality also, if these are not control at early stage.
Bt cotton have high doses of toxins but we are shocked that if they have high level of toxins then why these pest cannot die. Many peoples believe that the genetically modified crop have low level of toxins which leads towards the resistance of insect pests and don’t kill the boll worms at early stage.
Some varieties have zero toxin level which increase the insect pest’s level. The control of pink bollworm with insecticides are not control easily because these pests remain inside the bolls and develops excretion at the entrance points. Due to use of large number of insecticides they develop resistance therefore we need biological control agents for the control of this insect pests.
Strategies of biological control
There are three basic strategies for biological pest control:
- Classical (importation)
Where a natural enemy of a pest is introduced in the hope of achieving control.
- Inductive (augmentation)
Large population of natural enemies are administered for quick pest control.
- Inoculative (conservation)
In which measures are taken to maintain natural enemies through regular reestablishment.
Classical and inductive approaches give immediate pest control but they need heavy regular investment in purchasing natural enemies. The easiest and cheapest approach is to conserve already existing natural enemies.
Strategies to Enhance Beneficial’s
One of the most powerful and long-lasting ways to minimize economic damage from pests is to boost populations of existing or naturally occurring beneficial organisms by supplying them with appropriate habitat and alternative food sources.
Beneficial organisms such as predators, parasites and pest-sickening “pathogens” are found far more frequently on diverse farms where fewer pesticides are used, than in monocultures or in fields routinely treated with pesticides.
The following characteristics are typical of farms that host plentiful populations of beneficial:
- Fields are small and surrounded by natural vegetation.
- Cropping systems are diverse and plant populations in or around fields include perennials and flowering plants.
- Crops are managed organically or with minimal agrichemicals.
- Soils are high in organic matter and biological activity and during the off-season covered with mulch or vegetation.
- To conserve and develop rich populations of natural enemies, avoid cropping practices that harm beneficial. Instead, substitute methods that enhance their survival.
Advantages of biological control
- Cost consideration
By the use of biological control agents fifty to seventy five percent cost to control these pests have been described instead of chemical control within two years in the cotton growing area.
- Increase selectively
The natural enemies like predators and parasitoids are not kill by the use of this technique because these are host specific and not harmful for other organisms.
- Minimized safety concerns
By the use of chemicals the bio-control agents have long-lasting residual effects and these also injurious for environment. By the use biological control agents these bio-agents are don’t disturb and insect pests cannot develop resistance.
Authors: Shakeel Anjam1, Muhammad Adeel Arshad2, Wasim Yousaf2, Shehryaar Shahid2
1Department of Entomology, University of Agriculture, Faisalabad
2Institute of Animal and Dairy Sciences, University of Agriculture, Faisalabad