Tadpole shrimp

Systematic position: The tadpole shrimp (Lepidurus apus) belongs to the class Branchiopoda, order Notostraca, and family Triopsidae. This species is often referred to as a living fossil, as its basic body plan has remained largely unchanged for hundreds of millions of years, allowing it to thrive in ephemeral aquatic environments.

Affected crops and damage: Tadpole shrimp are primarily recognized as significant pests in paddy fields. They cause damage during the early establishment phase of rice growth. By rooting through the sediment and disturbing the soil, they disrupt the anchorage of young seedlings, often leading to the uprooting or burial of vulnerable rice plants.

Biology and lifecycle: The life cycle of Lepidurus apus is perfectly adapted to temporary water bodies like flooded rice fields. They survive dry periods by producing dormant eggs, known as cysts, which can remain viable in the soil for several years. Once the fields are flooded and temperatures are suitable, these cysts hatch rapidly, leading to a massive surge in population density within just a few days.

Nature of injury: Beyond mechanical damage to the roots, tadpole shrimp increase the turbidity of the water. This siltation blocks light penetration, which is vital for the photosynthesis of submerged or floating rice seedlings. In severe infestations, the cumulative effect of root destruction and inhibited photosynthesis can lead to significant crop failure and reduced yield potential.

Control measures: Management of tadpole shrimp requires a combination of water management and chemical intervention:

• Temporary draining of the rice fields to dry out the soil and eliminate larval stages.
• Precise land leveling to avoid localized ponding where shrimp might congregate.
• Application of selective insecticides registered for rice paddy use during the peak hatching period.
• Monitoring the water depth and temperature to predict potential outbreaks after initial flooding.