Cotton Insect Pest AMERICAN BOLLWORM

American Bollworm in Cotton

Common Name : American bollworm

Local Name : Hiravi bond ali

Scientific Name : Helicoverpa armigera Hub.

Family : Noctuidae

Order : Lepidoptera

Pest Category :Borer

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Description of Insect Stages:

Egg:

American Bollworm Stages of Life Cycle

Eggs are spherical with a flattened base laid on the tender foliage and calyx of squares and stem of the cotton plants. The surface is sculptured with longitudinal ribs. The Colour is white to creamy

white after oviposition. As the embryo develops reddish the brown band is seen centrally which gradually darkens and together with the rest of the egg becomes brown before hatching.

Larva:

Newly hatched larvae are translucent yellowish-white with brown to black head capsules. The thoracic and anal shields, spiracles, thoracic legs, setae, and their tubercle bases are also brown to black, giving the larvae a spotted appearance. The second instar is essentially similar but with the darkened ground color and lightened sclerotized head capsule, thoracic and anal shields, and thoracic legs. The third instar has a predominantly brown ground color. The characteristic patterning becomes more prominent and coloring generally darker in later instars. Considerable variations occur with shades ranging from green, fawn yellow to brown and their combinations. The host diet also plays a role to some extent in determining the color of the larvae. There are usually six larval instars.

American Bollworm is Attack for Square to Flower

Pupa:

The pupa is smooth surfaced, brown, rounded both anteriorly and posteriorly with two tapering parallel spines at the posterior tip. Females are on average heavier than males. Pupae are formed at a depth of 2.5 - 12.5 cm in the soil

Adult:

Adults are stout-bodied moths, greenish-yellow to buff to brown with darker brown or blackish markings. Males are light brown with a greenish cast. Females are darker than males. Moths have a circadian rhythm starting at dusk, continues through midnight after which it virtually ceases. Moths disperse over long distances to suitable crops from source hosts.

Nature of Damage:

American Bollworm in Adult Stage

The larvae feed on the leaves initially and then bore on to the square/bolls and seeds with their head thrust into the boll, leaving the rest of the body outside. Larvae show a preference for feeding on squares and flowers when present, however, feed on young bolls also. A single larva can damage 30-40 fruiting forms during its developmental period. The entry holes are large and circular at the base of the boll. Feeding on bolls can be extensive or only brief. These larvae spread Boll rot microbes, and the damaged bolls rot resulting in yield loss.

Symptoms:

The presence of frass held in place by delicate webbing is seen on squares fed by early instars. Damaged squares flare off and have feeding or damage holes on them. Excessive shedding of squares of variable sizes noticed. Clear-cutround feeding holes on squares and bolls with or without larvae are seen.

Life History:

The egg period is for 3 to 5 days. Larval and pupal periods last for 17-35 and 17-20 days, respectively. The life cycle is completed in 25-60 days. On an average female moth lays 700 eggs during its longevity of 8-12 days. The pest is polyphagous, voracious in feeding and has wide host range, various color forms and continues to occur year-round. They are multivoltine and have overlapping generations. The moths are highly mobile able to fly up to 200 km and thus have wider regional distribution.

Seasonal Dynamics:

First and second generations are found on several crops and weed hosts. The second generation usually infests cotton in low numbers. Populations increase dramatically during third and fourth generations with major outbreaks coinciding with peak squaring of first and second flush. Generations overlap due to the mixture of immigrant and local populations, and differential developmental rates. Seasonal phenology is host-mediated. Seasonal abundance is largely governed by the interaction between initial population size and timing, and host suitability and the environmental variables. There has been declined mean infestation due to H.armigera during 2005, over the last five years in Central India. The period of the onset of H.armigera varies with seasons. Lesser oviposition and higher larval survival and vice-versa occur. The damage to cotton fruiting structures is directly proportional coinciding with the crop growth with squares outnumbering flowers or bolls. The damage levels can reach as high as 30-40 % and the period of damage can extend into November - December months occasionally, however at low levels. Late season populations are high only during the outbreak of years. The peak damage among different years is not the same due to the differing fruiting cycle modulated by weather variables and response of crop to earlier attack by sucking pests or bollworms.

Prediction Criteria:

Prediction of the onset of H .armigera: Calendar year based on degreed any accumulations of 2450-2500 (DD) predict the onset of H.armiger oviposition on cotton.
Predicting the outbreak of H.armigera based on weather cum pest developmental variables:
Relative humidity levels > 70% throughout the day during August-September months, and dry spells followed by un seasonal rainfall distributed on many rainy days (with excess and/or more rainfall during the season), and rainfall amount more than 50 mm during October first the week leads to an outbreak of H.armigera. Steady increase in moth catches in pheromone traps (>2/trap/night) from mid-September, oviposition to the extent of more than two per plant on or before the first week of September, and larval incidence of more than two per plant for two subsequent or any two weeks between the end of September and mid October results in H.armigera damage severity. Degree of the severity of H. armigera on Kharif and rabi seasons are directly proportional.

Pest Management Options:

Adoption of closed crop seasons, discouraging monocropping and advocating crop rotation with nonhost crops reduce the food supply and shelter to H.armigera. Selecting Bt hybrids suited to the region and soil provide excellent control of H.armigera in addition to other bollworms. Pre planting cleans up measures during the off-season to keep the fields, their bunds and borders free of weed hosts are a must to break the link for the pest between cotton and alternate host crops. Pheromone traps of H.armigera can be set up @ two per ha that attract male moths to indicate the initiation and the degree of population development. The pheromone lures in the form of septa are to be changed once in 45-60 days with the trap height adjusted to one meter above the ground level in the early season, and one meter above crop canopy in the late season. The mechanical removal and destruction of the larvae during outbreak years are more successful than the insecticidal management wherein the control failure occurs. Practices that attract more attack by bollworms through increased vegetative growth such as closer spacing, excessive use of systemic insecticides during the early season for sucking pest management and excessive nitrogen application should be avoided. September is the month wherein H,armigera singly or in combination with Earias spp. cause excessive shedding of squares. Bollworm management at this stage should be based on the availability and damage level to fruiting parts on the plants beside the weather. The use of insecticides to be economical should commence only when the majority of plants have at least a few flowers and set bolls on them and the fruiting damage exceeds 10% in relation to total fruiting structures. Mechanical collection and destruction are advised when all the sizes of larvae occur simultaneously. Hymenopterous and tachinid parasitoids (e.g. Eriborus argenteopilosus, Campoletis chloride, Microchelonus spp. Palexorista laxa, Carcelio illota, and Goniopthalmus halli) are common on H.armigera that regulate the population during moderate levels of incidence. In Central, India watch should be kept on medium to large-sized bolls during September -October months from damage due to H.armigera. Protection of the first flush of squares using insecticides is highly difficult coinciding with the occurrence of H.armigera due to the overlapping and the consecutive generations. Therefore, the use of insecticides to manage H.armigera till 90% of fruiting structures on the plant are squares should be avoided. As the name indicates, bollworms should be suppressed only when there are bolls on the plant and boll damage is happening. The decision to spray should be taken not based on the level of damage but based on the retention of bolls on the crop and in conjunction with the presence of damaging larvae on the crop. When it is observed that the larvae of H.armigera are feeding on the bolls of two out of ten plants, during September and the first fortnight of October insecticidal application is to be done. The insecticides that are recommended with their dosages for H.armigera management are given in the table below. H.armigera management should be attempted with insecticides selected from IGRs, Spinosyn, conventional (OPs, and Carbamates) and other newer groups (Oxidiazine & Avermectin) in rotation considering the cost of the insecticide and anticipated level of yield saving from their application. There should be a minimum of 10 - 15 days interval between two sprays even at times of outbreaks to be cost-effective.

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American Bollworm Insect Pest are Control Chemical Name Suggesting to CICR, Nagpur

The amount of spray fluid varies more with the canopy size than with the crop age. It is recommended that power sprayers be used against bollworm management through insecticides. Normally 200-300 liters/ha of water should be used for a crop that had attained eight to sixteen nodes.