19:71.] FROGHOPFER BLIGHT IN TRINIDAD. 59 



The mongoose has been hehl responsible for tlic increase of the 

 froghoppers by clestroying their enemies. Comparisons of the food of 

 the mongoose in districts where it has been long abundant with districtsi 

 where it has only recently appeared, do not show any change of diet, 

 which would be expected if it had been responsible for the 

 extermination of birds, lizards, frogs and toads. Blight was known 

 before the introduction of the mongoose and the outbreaks of 

 recent years have not been correlated with the spread of this animal. 

 The conclusion reached is that the mongoose, although doubtless 

 undesirable, and possibly to a very limited extent contributing to recent 

 •outbreaks of pests, is not the one cause, nor is it even one of the most 

 important causes, of the outbreaks of froghopper blight in 

 Trinidad. 



The mongoose eats a number of rats and these can climb and have 

 been found destroying the nests of insect-eating birds. 



Birds, lizards, ants, spiders and other general insectivorous enemies 

 of the froghopper sometimes do harm by destroying its insect 

 -enemies. 



The spider and grasshopper enemies of the froghopper are destroyed 

 by fossorial wasps, while the former are also killed by an entomogenous 

 fungus (Gibellula). 



A worm believed to be parasitic, has been found in the pupa of a 

 Syrphid fly. 



In a figure an attempt has been made to show the relation of 

 the froghopper to its parasites and hyper-parasites. In the centre the 

 froghopper is shown and in the first ring round it all its natural enemies 

 •grouped according as they feed on the egg, nymph or adult. In the 

 outermost ring are the hyper-parasites or enemies of the enemies, and 

 in the intermediate ring are shown other hosts or foods of the parasites 

 and hyper-parasites. The arrows indicate that the animal at the tail of 

 the arrow destroys the animal at the head. A careful study of this 

 diagram will show the extraordinary complexity of the relationships and 

 the great difficulty of deciding whether any particular animal is desirable 

 • or undesirable. 



THE CANE ROOT FUNGI. 



Two distinct kinds of root fungi are found attacking the canes in 

 Trinidad. 



The Marasmius type mats together the lower sheaths of the cane 

 with a white dried-paste-like mycelium and produces spores on small 

 mushrooms. The Odontia-Himanlia fungus mats the lower sheaths of 

 the cane with a feathery mycelium and produces spores on a rough 

 granular surface grosvth on the outside of the sheath. 



])oth these fungi can exist in a healthy field of canes living only on 

 decaying vegetable matter and doing no harm. There is hardly a held 

 in Trinidad where traces of one or the other cannot be found after a 

 close search. 



Under certain little understood conditions, particularly when the 

 -canes are suffering from other causes, these fungi become parasitic and 

 invade the root and rootstock, causing greater or less destruction 



