Observations on Insects affecting the Turnip Crops. 309 



If it were not for numerous parasitical insects, which deposit 

 their eggs in these caterpillars, all chance of keeping them under 

 in the field would be fruitless : the most serviceable of these 

 agents is a little fly, which must be produced in myriads, for I 

 have sometimes found that every caterpillar had been stung by 

 this insect, which belongs to the Order Hymenoptera of the 

 Family Ichneumonides adsciti, and is named 



2. Microgaster glomeratus, Linnr It is black and thickly 

 punctured : the horns are thread-like, longer than the body in the 

 male, shorter in the female, and composed of 18 joints or up- 

 wards : the eyes are lateral, with three little eyes or ocelli upon 

 the crown : the abdomen is shorter than the thorax, depressed, 

 linear, smooth and shining; the basal segment is a little nar- 

 rowed, with the edges on the sides dirty white : ovipositor con- 

 cealed beneath the abdomen : the four wings are very transparent, 

 iridescent, with a distinct pitchy- coloured stigma on the superior; 

 tlie nervures lighter, the areolet open externally : legs bright 

 ochreous, hinder thighs black on the upper edge, darkest at the 

 apex, tips of their shanks and tarsi brownish, the apex only of the 

 four anterior brown : length a little more than one line ; expanse 

 three (fig. 10). 



This minute Ichneumon-fly lays numerous eggs in the cater- 

 pillars of the White Cabbage -Butterfly, which hatch and feed 

 within their skins in almost incredible numbers, the victim feed- 

 ina: ai^d o^rowinof until it has attained its full size, when, instead of 

 changing into a chrysalis, like fig. 8, a number of fleshy maggots 

 (fig. 11) come through its skin, and form beautiful little oval 

 silken cocoons in masses beneath and around it, like the balls of 

 the silkworm in miniature (fig. 12) ; they are bright yellow; and 

 I counted sixty- seven which issued from one unfortunate larva. 

 On opening a caterpillar thus infested, it will be found full of little 

 fat maggots (fig. 11), which eventually consume all the muscles, 

 leaving only the alimentary canal untouched : those in my pos- 

 session, which spun up in September, hatched the beginning of 

 the following May, when they were ready to commence their in- 

 valuable operations upon the early broods of the White Cabbage- 

 Butterflies. Reaumur says the Microgaster pierces the skin of 

 the caterpillar with its short oviduct, and deposits an egg; it then 

 v/ithdraws it, and repeats the operation, until thirty eggs or more 

 are introduced into the living caterpillar, and they are inserted 

 sufficiently deep not to be cast off with the skin : the maggots 

 avoid feeding on the vital parts, so that the caterpillar does not 

 die until two or three days after the parasites have eaten their way 

 out to spin their cocoons, but the caterpillar, being exhausted, gene- 



* Curtis's Brit. Ent., fol. and pi. 321 ; Guide, Genus 554, No. 54. 



