Aphididae of Formosa. — 3. 73 



The 5th cantennal joint of tlie 3rd and 4tli instars of Lncliims tJmJafoliae 

 Theob. is usually provided with a sniall aensorium in addition to the apical primary 

 one. 



Dilachnus formosanus n. sp. 

 DUaclmm qi., Takahashi, Apliididae of rormosa-2, p. 46 (1923). 



AVingless viviparous female. 

 Difi'ers from Dilachnus ]>in!formosanm Takah. in the following characters: 

 Body larger, measuring about 4 or more mm. in length. More yellowish 

 brown in general colour. Nymphs ;vith a somewhat greenish tinge. Antennae 

 provided with shorter hairs which are fewer in number; the 3rd joint longer than 

 the 4th and 5th taken together; tlie 5th almost as long as the 4th, with a sensorium 

 near the usual apical one; the relative length of joints about as follows: III-132, 

 IV-52, V-50, VI- 45. Hairs on tlie leg's shorter. The 2nd tarsal joint relatively 

 shorter. 



Winged viviparous female. 

 Very closely resembles D. pini/m-mo.sanu.1 Takah., differing from it, however, 

 in the following characters: 



Body more yellowish brown in general colour. Hairs on the antenna shorter 

 and fewer in niunber; the 3rd antennal joint longer than tlie 4tli and 5th taken 

 together; the 4th and 5th equal in length; the relative length of joints about as 

 follows: ni-140, IV-57, V-57, VI-48. Legs with shorter setae; tarsi stouter. 

 Length of body about 3.7 mm. Antenna-1.6 mm. 

 Fore wing-about 4.0 mm. 



In I), piniffn-jnomnus Takah., tlie 3rd antennal joing is almost as long as the 

 4th and 5th taken together and the 5th is longer than the 4th. 



Nymph. 



Key to instars. 



( 1 ) Antennae 4-jointed The 1st instar. 



Antennae 5-jointed The 2nd instar. 



Antennae 6-jointed (2) 



( 2 ) Body much smaller than tlie adult. Wing-pads not well 



developed The 3rd instar. 



Body only slightly smaller than the adult. Wing-pads well 



developed The 4th instar. 



(The first instar) Antennae 4-jointed; the relative length of joints about as 



