306 



bugs. Solutions of sodium cyanide proved efficacious, but more from 

 the effect of the fumes, than as a stomach poison. Such sohitions 

 are too dangerous to be recommended for general use. 



The best of the poisons tested was a lead acetate solution, 2 oz. to 

 1 U.S. gal. water. Fresh maize stalks cut and dried for several days 

 were soaked in this solution and spread on the ground, being covered 

 lightly with straw to prevent rapid drying. At the end of the first 

 day 104 dead bugs were found to the square inch, while at the end of 

 the sixth there were 11, the stalks not having being remoistened in 

 the meantime. 



WoLcoTT (G. N.). An Emergence Response of TricJwgramma minutum, 

 Riley, to Light. — Jl. Econ. Entom., Concord, N.H., xi, no. 2, April 

 1918, pp. 205-209. 



In 1917 the author collected large numbers of egg-clusters of the 

 sugar-cane moth stalk borer, Diatraea §accharalis, F., 62'6 per cent. 

 of which were found to be parasitised by the Chalcid, Trichogramma 

 minutum. The number of eggs in the masses varied from 3 to 71. 

 The eggs are creamy white when laid, but turn yellow in a few hours, 

 and orange colour in a couple of days, and just before hatching the 

 dark brown head of the young caterpillar can be seen through the 

 transparent shell. Clusters parasitised by T. minutum become black 

 soon after parasitisation and remain this colour even after the 

 emergence of the parasite, owing to the contained black debris, 

 making easy the determination of parasitised eggs and clusters. 



The eggs are impartially deposited on any part of either surface of 

 the leaf, but are generally more numerous from the centre to the tip. 

 In the laboratory, experiments to determine the influence of hght 

 on emergence were made by enclosing bits of leaves bearing egg- 

 masses in small glass tubes, corked at one end, a plug of cotton wool 

 being placed at the other, to absorb the moisture. Both young 

 larvae of D. saccharalis and adults of T. minutum were found to be 

 positively phototrophic to a very marked degree. 



To determine the emergence response of adults of T. minutum to 

 hght, the tubes with the corks removed were placed with the open 

 ends turned towards the light, and the adults were counted as they 

 left the tubes, the tubes having previously been kept in the dark in 

 a large tube. They were then left in the window for an hour, being 

 examined again at the end of that time and the escaping T. minutum 

 being counted as before, after which they were returned to the dark 

 tube. 



The ratio of the total number of adults that had emerged before 

 exposure to hght compared with the total number that emerged 

 afterwards, expresses what has been assumed to be the emergence 

 response to hght. 



It was found that the emergence response was not so strong several 

 days after collection, which may have been due to uimatural con- 

 ditions of iQoisture, or to the lessened power of an organism to respond 

 to hght when it has received only J^ the normal amount. It was also 

 noted that the emergence response is not as strong in the late morning 

 or afternoon as earher in the day. In the field emergence has been 

 noted from 7.15 to 8.45 a.m., the normal time of emergence being 

 approximately two hours after sunrise. 



