Biology and Management of Cotton Grey Weevil: A Review

Cotton grey weevil is becoming a primary pest of agricultural and horticultural crops all over the world including Pakistan. The various management strategies such as chemical, biological and cultural have been adopted against this pest throughout the globe. The previous published literature was reviewed with the aim to evaluate the best strategy among all strategies to control the pest. Male is shorter as compared female with approximately 6.0 to 8.5 mm length. Adult feed on the leaves and cause huge crop losses. The current reviewed literature concluded that chemical control can give quick control of adult due to their fly ability while control of pupae, larvae and eggs is difficult due to their location in or on the soil. The excessive use of chemicals to control pest can caused mortality of other biological fauna. To avoid the excessive application of chemicals, biological and botanical control should be promoted and applied that will prove best option against the current pest.

This pest attack can by controlled by traditional techniques including insecticidal applications.Owing to its flight behavior, hiding ability, chemicals-based practices are considered not good for the control of its attack.The weevils can be eliminated from plants by shaking a branch to collect and dumped into the soapy water.The insecticides recommended by the government has applied in field for pest attack control and updated yearly.
The IPM practices such as carious agronomic practices, chemicals, biological practices and mass trapping of adults have been developed and implemented in all over the world where this pest attack has severally found.

Taxonomic classifications
Myllocerusis most common genus of grey weevil which has different species and subspecies which attack on more than 20 different crops in Indo-Pak subcontinent (O'Brien et al., 2006) (Shanthichandra et al., 1990;& Thomas, 2000).

Biology and life cycle Eggs
The female weevil laid up to 360 eggs on organic materials on the soil surface within the 24 hours.The eggs are oval shaped (0.5 mm length) creamy white in color laid in clusters form.At near to hatching creamy color change into brownish (Atwal, 1976).

Larvae
The white color grub with brownish red head size ranges 1-4 mm in length from first to later instar larvae (fourth).They feed on the roots of plants under the soil and then pupate inside the soil (Butani, 1979).Pupal stage Pupation took placed in soil which lasted 5-7 days.

Adults
The adults of this weevil may range from 6-8.5mm in length while female weevil is larger than male (1-2 mm approximately), and weevil have dark dotted to greyish elytra with yellow colored head.The weight of the female weevil twice that of male (George et al., 2015).The weevils feed on the margin of leaves and eating away small patches of leaf lamina, adult lives vary in both seasons from summer (8 -11 days) to winter (4-8 months) (Butani, 1979).Total life period from egg to adult Its total life period from egg to adult was three weeks that reported by many researchers.The variations had been recorded by many early researchers on the basis of environmental conditions (Thomas, 2005).No. of generations 8-10 number of generations per year had been reported by many scientists (Josephrajkumar et al., 2010).Damage Leaf notching can cause during severe attack of adults that feed on leaves.Adult feed on the margin or corner of leaf and during severe attack of pest, complete defoliation of leaves occurred.It has been observed that adult mostly feed on the new leaves of plant and resulting plant decline and even stunting the plant growth (Arevalo & Stansly, 2009;& George et al., 2019).Management Quarantines Several species of the Genus Myllocerushas considered pests but no patent information on a specific quarantine was found.Although, few references exist on this weevil may be considered as a pest of quarantine significance.

Cultural Control
The grub of this weevil can be killed by frequent hoeing, trap cropping is a very good strategy to eradicate cotton grey weevil from the cotton field.Integration of cultural practices with other practices is a tremendous potential for the management of cotton grey weevil.By use of these practices, farmer will less dependent on the use of chemical based products for insect pest control and are very helpful for small scale farmers.

Biological control
Several natural enemies are helpful for the control of Myllocerus undecimpustulatus undatus.Braconid parasite Dinocampus mylloceri Wilkinson (Pruthi and Batra, 1960) and semi-parasitic mite was recorded as natural enemies of this weevil.In India, semiparasitic mites have been observed in the body of cotton grey weevil during experiment (Geetha et al., 2013).These all may consider as biological control agents for this weevil.

Chemical Control
Several insecticides carbaryl, acephate and pyrethroids are effective for controlling of leaf-feeding insects and these are especially for Myllocerusspp., to suppress the populations.However, larvae buried inside the soil and pupate, so methyl iodide and methyl bromide soil fumigation technique have good option as a fumigant against these type of insects (Eayre et al., 2000;& Waggoner et al., 2000).( Arévalo & Stansl, 2009) applied chlorpyrifos on ground and foliage which was provided better control against the cotton grey weevil in Florida.