78 
Journal of Agricultural Research 
Vol. I, No. i 
no parasites present during January, 1913, among the larvae feeding in 
cowpeas. From this fact it naturally follows that the season of greatest 
injury to forage crops from leaf-miners will be during a period of pro¬ 
longed cool weather, when the temperature will naturally be unfavorable 
to the rapid multiplication of the parasites. This is precisely the con¬ 
dition that exists where there are destructive outbreaks of the green 
bug (Toxoptera graminum Rond.) as then the native parasites are unable 
to keep the pest in check. Of the life history of most of the parasites 
reared in connection with this leaf-miner comparatively little is known. 
Diaulinus begin! Ashm.—The parasite most thoroughly studied, as 
well as the most abundant, widely distributed, and hence most important in 
the control of the host 
is a small chalcidoid, 
Diaulinus begini 
Ashm. (fig. 9) ; the larva 
of which feeds exter¬ 
nally upon the body of 
the Agromyza larva. 
This parasite has been 
reared from mines in 
leaves of alfalfa, clover, 
cowpeas, and rape in 
Indiana, Kansas, Ari¬ 
zona, New Mexico, 
Fig. 9. —Diaulinus begini , a parasite of the serpentine leaf-miner. At California, Utah, Wy- 
left, hind leg of Diaulinus websteri. Greatly enlarged. (Original.) • i xi i i 
ommg, and Idaho by 
different members of the Bureau of Entomology and from mines of 
Agromyza parvicornis in corn leaves at Salt Lake City, Utah. 
The junior author was able to observe all stages of its development at 
Salt Lake City. The female parasite wanders about over the leaf until 
she locates the Agromyza larva in its mine below; then, pushing the ovi¬ 
positor through the membranous tissue of the leaf which constitutes the 
roof of the mine, she places the egg upon the body of the host larva. 
The egg, as observed upon the surface of the host larva, is smooth, 
translucent, oblong, but rounded about equally at each end, and is about 
0.5 mm. in length. The egg period is short, probably not lasting more 
than one or two days. The young larva feeds externally upon the body 
of its host, which dies while the parasitic larva is yet very young. Often 
the presence of the parasitic larva can not be detected on the body of 
the host without the aid of a microscope. The host larva is invariably 
dead whenever one of these larvae, even though apparently just hatched, 
can be found on its body. Occasionally two larvae feed on the body of 
a single host larva, and in one case both parasitic larvae were observed to 
complete their transformations and emerge. The larval period is seven 
days. Figure 10 shows the full-grown larva. Pupation takes place 
