The Aphis or Plant Louse. 



By D. SYM SCOTT, Forester, Ballinacourte, TirPERARY. 



This may be termed the real plant louse. Almost every plant supports 

 a different variety of this insect. The Aphis forms a numerous family, 

 and groups with the " Larch Bug " in the sub-order HomoiJtcm, order 

 IV., Fihynrhota Imeda. The insect is more or less flask-shaped, with a 

 pair of antennae, six long slender legs, two tubes protruding posteriorly, 

 and is winged and wingless. 



The true history of the Aphides is as yet greatly enveloped in 

 obscurity ; still we are always finding out something new regarding 

 them. The most astonishing feature in the insect is its extraordinary 

 multiplying proclivities. Each generation is estimated to number on 

 an average one hundred, and there are in most instances ten genera- 

 tions in the year. They are asexual, multiplying by a generation of 

 fruitful virgins. 



The process of incubation is carried on in an abdominal cavity, such 

 as many of the minuter insects are endowed with, and which admits 

 of internal germination, being a process similar to the reproductive 

 system by external buds. Steenstrupt advanced a theory that 

 Aphides were produced on the principle of " alternation in genera- 

 tion," or each brood differing from the last, until a change of circum- 

 stances, such as the alternating generation being exhausted, when the 

 original perfect insect was produced. Several other theories were 

 started regarding the Aphis, but for want of sufficient data to work 

 on have never been well founded. 



It was long supposed that ants were their natural enemies. This, 

 however, is not the case, as they seem to live on the most friendly 

 terms. From the posterior tubes of the Aphis a sort of sv/eet fluid 

 is exuded, which is highly relished by the ants ; so much so is this 

 the case that the Aphis is called the " ant's milk cow." Birds have 

 no particular desire to pick them ; at all events, I have never 

 observed them frequenting spots infested with the insect. My own 

 opinion is, we must look for some small insectivorous animal or insect 

 as their enemy. In a field here every thistle is actually black with 

 Aphis, and paying particular attention to their development, I find an 

 infinite number of skeletons adhering to the thistle, which in a 

 measure supports my opinion that their enemy is much smaller than 

 themselves. Perhaps some of your readers will favour us with their 

 experience and views on insects infesting forest trees. 



