Biological Control Of Invasive Plants
University of Florida	Aquatic, Wetland and Invasive Plant Information Retrieval System

Hydrilla
Hydrilla verticillata

Basic hydrilla information and photos
Detailed hydrilla information and photos


Hydrilla is a submersed plant that was introduced into Florida as an aquarium plant. Since the 1960s, hydrilla has become the "number 1" aquatic weed in the state, filling lakes and rivers. It has spread rapidly throughout the southern US, and now occurs as far north as Delaware, as far west as California.


The first biocontrol insect released against hydrilla in the US was the Pakistani hydrilla tuber weevil (Bagous affinis). First releases were made in 1987. Unfortunately, this weevil feeds on hydrilla tubers only when water recedes from the plants, a situation that occurs in Pakistan but is rare in Florida, except when lakes are drained. Therefore it has been difficult to establish field populations. The efficacy of this hydrilla tuber weevil, as well as another released Bagous species is still being evaluated.


• Bagous species Hydrilla tuber weevil, adult in sand
• Bagous affinis Hydrilla tuber weevil, adults on tuber
• Bagous affinis Hydrilla tuber weevil, larva on tuber
• Bagous hydrillae, adult on submersed hydrilla in quarantine
  
• Bagous hydrillae, adults and fish in quarantine
  
• Bagous hydrillae, adult feeding in hydrilla stem
  
• Bagous hydrillae, larvae in hydrilla stem
  



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And then there are the flies. Another hydrilla biocontrol agent, Hydrellia pakistanae, was first released in Florida in 1987. The hydrilla leaf-mining fly is from Pakistan. Only the larvae of this insect damage hydrilla, by mining the leaves. Its life cycle is short at about 20 days. Initial establishment problems were overcome by 1990, and now field populations are established in several places in Florida.


Other Hydrellia species have been identified, investigated and released against hydrilla, including Hydrellia balciunasi, an ephydrid fly from Australia.


• Hydrellia pakistanae Hydrilla leaf-mining fly, adult on leaf
• Hydrellia balciunasi Hydrilla leaf-mining fly, adult on leaf
• Hydrellia balciunasi Hydrilla leaf-mining fly, leaf damage
• Hydrellia pakistanae Hydrilla leaf-mining fly, eggs on leaf
• Hydrellia pakistanae Hydrilla leaf-mining fly, pupa in hydrilla

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