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BUG OF THE MONTH

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Poplar Twiggall Fly (Hexomyza schineri)

 

Picture by Whitney Cranshaw

Colorado State University.

 

 
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Picture by Joseph L. Sandoval

 
 

 

 


Adults are stout, shiny, dark flies about 0.!6 inch long.The developing gall fly is a greenish-yellow maggot.This insect causes

galls on the current seasonís twigs.Obscured by leaves, the original galls rarely are noticed until leaves fall in autumn.However, the galled tissues continue to grow and swell.Ultimately, galls become large knots on trunks and larger branches, giving the plants a gnarled, bonsai-like appearance.During subsequent years, the galled area is incorporated into the growing twigs and branches and ultimately may appear as large swollen bands on trunks and branches.Although these old injuries produce a permanent disfigurement, they do not seem to threaten tree health.Galling is most common on younger trees that produce a lot of succulent new growth.

 

 

 

 

 

 

 

 

 

 

 


Once a tree has been attacked the galled tissues continue to grow and swell, and the galled areas are incorporated into the growing twigs and branches and may ultimately appear as large swollen bands on trunks and branches.

Poplar twiggall fly damage has been noted on Quaking Aspens in and around Santa Fe, since around 1994 according to Patrick Torrez, Santa Fe County Extension Agent.

 

Life Cycle:The poplar twiggall fly overwinters within the gall as a full-grown, yellow-green maggot.

 

 

 

 

 

 

 

 

 

 

 

Picture by Whitney Cranshaw

Colorado State University.

 

 

Picture by Joseph L. Sandoval

 
 

 


Pupation occurs within the gall in late winter or early spring.The majority of the pupae then drop to the ground.At the time that new growth forms, the adult flies emerge from the pupae and become active.During the day, they rest and sun themselves on leaves.After mating, females move to developing twigs and insert eggs into the stems.The larvae hatch from these eggs and produce the distinctive swelling in response to their feeding.Areas below buds appear to be particularly flavored sites for galls.As the stems continue to grow, the area where eggs were laid becomes increasingly swollen.At first, the swelling involves a fairly indistinct enlargement.However, within two months, the full sized gall is usually present.The developing gall fly maggot grows slowly within the gall all summer.It is difficult to find until late summer and fall, when it grows rapidly, filling a small cavity within the swollen area of the twig.Individual galls typically contain two to three larvae.There is one generation per year.

 

 

 

††††††††† Pacific Northwest Insect Management Handbook.<http://weeds.ippc.orst.edu/pnw/insects?24LAN04.dat>

 

 

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Picture by Whitney Cranshaw

Colorado State University.

 

 
 

 

 

 

 

 

 

 

 

 

 


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Picture by Joseph L. Sandoval

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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Picture by Joseph L. Sandoval

 
 

 

 

 

 

 

 

 

 

 


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Picture by Joseph L. Sandoval