Mahasena corbetti, the coconut case caterpillar, is a polyphagous species of bagworm. This species is classified as leaf-eating pest caterpillars that produce tough silk out of their bags from dried foliage. Currently, M. corbetti is considered a 'pest of quarantine importance' in multiple countries and is included on the list of dangerous pests in the Malaysian plant quarantine act.
Distribution
Although initially native to Malaysia, this destructive leaf defoliating pest has now been recorded in many Southeast Asian regions and Pacific islands, including Thailand, Peninsular Malaysia, Sumatra, Java, Borneo (Brunei, Sabah), Solomon Islands, Samoa, Papua New Guinea and the Philippines. As of 2015-2016, it was identified for the first time in a region bordering India and Bangladesh as a pest of areca nut (Areca catechu L.) plants. Because the larvae of M. corbetti are most active as pests during bright sunlight, this species thrives in areas that get a lot of natural sunlight and heat.
Morphology
Male M. corbetti larvae (without the case) are approximately 15-20 mm long. They have a brown thorax and head with a light yellowish brown abdomen. Their cases (or bags) are considerably smaller than that of their female counterparts. Gender determination of the bagworm is difficult in the larval stage, but size distinction in the pupal case lets us approximately determine the sex of the pest before it reaches the adult stage, since females generally have larger cases than males. In the pupal stage, the male pupa are approximately 12-15 mm in length and 3-4 mm in diameter while the female pupa are approximately 20-25 mm in length and 10-12 mm in diameter. This pupa is messy looking in appearance and is made from randomly shaped leaf pieces, stalks and other natural materials. During the pupae stage, male M. corbetti undergo metamorphosis and turn into moths. These male moths are generally varying degrees of black to brown with white scales on some. They have thinly scaled and often transparent wings and prominently pectinate antennae. Adult females - who spend the entirety of their lives in the pupa - are apterous, cylindrical, and creamy-white with either no or greatly minimized appendages. Both males and females lack mouthparts. The male pupa being a moth with eyes, antenna, and wings (wingspan of about 22-26 mm) marks sexual dimorphism in M. corbetti.
Anatomically, only adult male individuals of the M. corbetti species can be taxonomically identified. However, in this species, there are much fewer males than females and a male takes about 4-5 months to emerge after fertilization, which is why the DNA barcode is more commonly used for taxonomic identification. This DNA barcode was determined by sequencing a standard barcoding region of the mitochondrial oxidase I (COI) gene.
Life cycle
The entire life cycle of M. corbetti is 110-140 days with a stage by stage breakup as follows: Egg:10 to 16 days Larva: 60 to 95 days Pupa: 14 to 26 days Adult: 7 to 10 days (male) Neonatal larvae have well developed sclerotized head and thoracic legs as well as weak abdominal forelegs. After emergence from the egg, they partake in an initial dispersal event. This dispersal event has been recorded but not well understood for this species. All that is known is that M. corbetti larvae are dispersed by wind, vehicles, animals, or humans.
The first thing the larvae do once they land on their host is construct their case from nearby foliage. This case is integral to their survival, as it is seen that if larvae are removed from the case, they usually do not construct a new case and will end up dying. This case provides protection, anchorage, and a microclimate environment integral to their survival. If attacked by predators, this case can be lengthened into a sleeve that provides absolute protection for the larvae. The larvae then attach to their host via a strong silk thread, walk around their host, and begin to scrape the surface of the leaves of their host. Whenever the larvae of M. corbetti are resting, feeding, or mounting, they will ensure that the case is anchored to the leaf via a tough silk thread to prevent falls/contact with the ground.