66 PLANT-BUGS INJURIOUS TO COTTON BOLLS. 



and one-half millimeters long, shortly after being brought into the 

 laboratory from a cotton field, killed and partially ate a first-instar 

 nymph of a Pentatomid of the genus Thyanta. 



Attacking adults. — No invertebrates are known to attack adult con- 

 chuelas, nor has the writer found any reference on this point in the 

 case of other Pentatomids. Broken and empty shells of adults have 

 been found in> cotton fields in midsummer, but there is no direct evi- 

 dence to show this to be the work of predatory enemies, although it 

 may be suspected. 



BIRDS. 



In spite of much evidence to the contrary, scattered in various 

 scientific publications, it is the prevalent idea that the offensive 

 odor of bugs protects them from birds. Without this supposition 

 the object and origin of the odoriferous glands may be difficult to 

 explain, but studies in the feeding habits of insectivorous birds has 

 shown that in most cases Pentatomid bugs are eaten at least to the 

 extent of the proportion of their numbers to the numbers of other 

 insects of the same and larger size. Further, it would seem that 

 some birds, like the crow, possess a predilection for insects of pungent 

 or otherwise strong taste or odor. Careful studies have been made 

 of the feeding habits of about 20 common American birds. Almost 

 without exception Pentatomids (variously referred to as ''stink 

 bugs," ''soldier bugs," and "Pentatomids") are included in the diet 

 of each of these birds, amounting on the average to about 3 per cent 

 of all the food. 



Thus far no specific observations have been made for the purpose 

 of determining the extent to which birds feed upon the conchuela. 

 It is evident, however, that there is some important influence com- 

 bined with egg parasitism to produce in midsummer the marked 

 reduction in number of these insects observed both in Mexico and in 

 Texas. The egg-parasites effectually check the multiplication of the 

 pest after the month of July, but the diminution in numbers of the 

 adults remains unexplained. In the laboratory, protected from their 

 enemies, the life of the adult conchuela extends over many weeks, 

 27 specimens collected at Tlahualilo between July 6 and July 10 

 averaging over two months each. 



It is inconceivable that the difference between field and laboratory 

 conditions should be so great that, of the insects of the field on July 

 10, over 60 per cent should die from natural causes before August 1, 

 while in the laboratory less than 5 per cent should die during the 

 same period. Furthermore, if the numerical decrease in question 

 had been due to natural exhaustion of vitality of the adult insects, it 

 would be expected that many dead specimens would have been 

 found in the cotton fields. As a matter of fact, dead specimens were 

 exceedingly rare and the few found gave evidence of having been 



