Megastigmus spermotrophus (Torymidae)

Douglas-fir seed chalcid


Adults:

Adult male Megastigmus spermotrophus seed chalcid. Females are amber coloured wasp-like insects, about 4.0 mm long, with a long ovipositor which curves up over the abdomen. Males are lighter in colour, almost yellow, about 3.0 mm long (as seen in photo).



Larvae:

Larval Megastigmus spermotrophus living within a seed. White, legless grubs, complete whole development inside a single seed.



Damage:

After the adult Megastigmus spermotrophus emerges from the seed, an emergence hole can be seen. Female chalcids deposit an egg into each seed selected in a young cone by means of her ovipositor, no entry marks are made by the ovipositor. The larvae feed only on seed contents, each one destroying a single seed. After devouring the contents it remains within the seed coat. There is no external evidence of damage until the adult emerges, after which a clearly defined emergence hole is evident. Prior to adult emergence insect damage can be detected only by seed dissection or X-rays. Larvae remain over winter in the seeds, either in the cone which may remain on the tree, or in the litter. It pupates in the spring.



Principal Hosts:

Douglas-fir and big-cone Douglas-fir (Pseudotsuga macrocarpa).

Economic Importance:

Usually less destructive than B. colfaxiana and C. oregonensis, but can be a problem in seeds destined for export.

References and Links:

EAG: 548, 551;

Fact sheet.

Additional Images:

Female seed chalcid. Sliced infested cone showing larvae and empty seeds. Radiograph of infested, healthy and infertile seed. Can you see the larvae?  (Crescent-shaped, legless).