BIOLOGICAL NOTES ON THE PARASITES. 55 



FREQUENTATION OP NECTARIES. 



The feeding habits of adult hymenopterous parasites have lonji; 

 escaped observation, but witliin recent yiears the intensive study of 

 parasites has proved that very Httle can be accompUshed in the prop- 

 agation of parasites unless they can be fed. In the case of the para- 

 sites of the boll weevil it is impossible for the adults to obtain nour- 

 ishment from the host in which they are ovipositing, as has been 

 proven in the case of parasites of externall}' feeding insects. The 

 host plant of the boll weevil, however, furnishes the desired food. 

 The nectaries of cotton are about as plentiful as those of any other 

 plant. The majority of varieties of cotton have three large nectaries 

 on the leaves and also have them on the outside and inside of the 

 involucre, as well as on the inside of the flower. Frequent observa- 

 tions of cotton plants which were producing considerable nectar have 

 enabled us to observe practically all of the parasites of the boll 

 weevil, as well as all of the ant enemies and many other insects. 

 Some of these insects which ^dsit the nectaries are injurious to the 

 cotton plant, but the majority seem to be beneficial. 



The quantity of nectar secreted by various varieties of cotton is 

 quite variable. The variety wliich seems to secrete more than any 

 other which has been observed is the Egyptian Mt Afifi. This variety 

 is frequently surrounded by large numbers of beneficial hymenop- 

 terous insects, although at the same time it appears to be very sus- 

 ceptible to boll weevil attack. « 



HELIOTROPISM. 



The majority of the hymenopterous insects which have been under 

 observation in this investigation appear to be positively heliotropic. 

 In general this tendency can be utilized in rearing-cage technique to 

 induce the parasites to go into small tubes placed in the rearing boxes, 

 from which they can be easily removed. It has been noticed in 

 rearing cages in which there were growing plants with plenty of food, 

 air, and heat, that the parasites sought the lightest portion of the 

 cage rather than the plants wliich could give them some shade from 

 the hot sun. 



The activity of the parasites is greatest when the sunhght is most 

 intense. Observations at the nectaries of the Egj''ptian cotton con- 

 firmed this. When the sun was shining the parasites were very 

 active at the nectaiies and fl}Tiig around the plants, but when a 

 cloud passed over they seemed to disappear entirely. On cloudy 

 days none of the Hymenoptera, except the most industrious bees and 

 wasps, was to be found at the nectar. Trelease (1879) states that 

 "the extrafloral nectar of the cotton plant is far more abundant 

 during night and in the early morning than at any other time, and 



