i8 INDIAN FOREST INSECTS 



II. General Remarks on the Methods by which the Insects of Use to 



the Forester accomplish their "Work. 



The insects of use to the forester may kill either the egg, larva, pup)a, 

 or imago stage of the host insect upon which they prey, or they may destroy 

 more than one of these stages of their host. 



(a) Predators, or Insects which prey directly upon injurious 



FOREST insect PESTS WHICH THEY COMSUME AT ONCE AS FOOD. 



Investigation in the Indian forests has shown that the forester is 

 assisted in his work of protecting the trees from injury by a variety of insect 

 helpers. 



Up in the North-Western Himalaya probably one of the chief insects 

 of importance in this category is the scolytid bark- and wood-borer 

 predator Thanasimus himalayensis (p. i86), discovered in 1902, 

 the imago of which feeds voraciously upon most of the 

 Himalayan coniferous bark- and wood-boring scolytids. This 

 insect takes the place of the well-known Clems formicarius 

 of the German coniferous areas. The grubs of this beetle 

 (which preys upon the scolytids outside the tree) feed 

 upon the bark-beetle grubs in their tunnels in the bast 

 layer. 



Fig. \\.— Tha- a second species of the same family, Tillus, enters the 



>/astmus hwia- t^jf^j-,gis of the bamboo-borer Dinodems minutus, and feeds upon 

 ayen-Ms, . ., ^j_^^ larvae and pupae of this bostrychid {vide p. 186). 



prCQclCGOUS up- -T JT J •- X 



on Scolvtidae Another useful bark-beetle predator in these forests is 



in the Western the histerid Niponius canalicollis, first discovered in igoi. 



Himalaya. This beetle follows the bark-beetles into their tunnels, notably 



Scolytus and Polygraphus, and preys upon the eggs and grubs 



and pupae in one or more of the metamorphoses. Another species 



of the same genus preys in a similar manner upon the sal Sphaerotrypes 



beetles in the United Provinces and Assam, and upon the Sphaerotrypes of 



the Anogeissus in Madras. Several other histerids (Paromalus, Platysoma) 



prey in a similar manner upon the scolytid bark-borers Polygraphus and 



Tomicus, and upon the wood-borers Rhyncholus and Hylastes. Other histerids, 



again, species of the genus Teretviosoma (p. 104), prey upon the bostrychid 



wood-borers Sinoxylon crassum (p. 152) and S. analc (p 167), which infest the 



sissu-tree. 



Observations carried out over a period of ten years have, I think, estab- 

 lished the fact that certain species of histerids have adapted their mode of 

 life to that of the insects upon which they prey. Those species, so far as at 

 present observed, which prey upon bark-boring Scolytidae obtain entrance to 

 the tree by crawling down the tunnels made by their hosts. Species of 

 Niponius, Platysoma, Paromalus, Tcretriosoma, Tcretrius, all act in this manner. 

 This point is further referred to under the familv. 



