498 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



Check to Experiment VIII 



Sept. 30: Started cage of 50 weevils under exactly similar conditions to Experiment 

 VIII except that no fungus was intentionally introduced. 



Nov. 25 : One dead of S. globulifermn. 



Dec. 18 : Forty-five living weevils, 3 dead (2 of S. glob id if er urn), 1 lost, 1 killed by S. 

 globuliferum removed. 



Note: No Sporotrichum appeared in this cage until 2 months after starting experi- 

 ment. 



Summary of Infection Experiments 



In the early experiments when tight, unventilated tin boxes were 

 used, complete mortality from the fungus disease occurred within two 

 weeks, in the case of Experiments II and III in 12 and 10 days respec- 

 tively. Conditions wei'e of course optimum for the growth of the 

 fungus and very unnatural for the weevil. 



In the early battery-jar cage experiments under supposedly less 

 favorable conditions for the growth and spread of the fungus, almost 

 as good results were attained, the majority of the weevils dying of the 

 disease within ten days to two weeks. In the case of Experiment VI, 

 where the weevils were less crowded than in any experiment but Ex- 

 periment I, all died in 12 days. In the case of Experiment I where 

 conditions most closely approached those in the field in the proportion 

 of the number of weevils to the area of the cage, a somewhat longer 

 time was necessary to kill 3 of the 5 weevils, namely 17, 18 and 33 days 

 respectively. The last weevil to die in this cage probably either es- 

 caped or conquered the first infection which in this case was attempted 

 by a short exposure to the fungus spores followed by isolation in a clean 

 cage. 



In the later experiments with weevils of the new generation, consid- 

 erable resistance to the fungus developed. At this time a majority 

 of the weevils were killed in 3 weeks, but often several were able to 

 survive for one or two months. Some of this difference in mortality 

 between the two seasons may possibly be attributed to the fact that 

 the cages dried out faster in mid-summer and fall, so that often the 

 sand or dirt in the cage became almost bone-dry before this condition 

 was rectified by sprinkling the interior of the cages. However, dis- 

 sections and blood examinations of some of the weevils from these 

 cages indicated that some individual weevils were more or less immune 

 at this season. This immunity is deduced from the cytolytic phenom- 

 ena observed in the blo®d of the weevil dissected under Experiment 

 VIII. 



It may be of interest to note in this place that Hypera adults appear 

 to be rather resistant to the well-known entomogenous fungus Met- 

 arrhizium anr^oplicc Sorokin. Laboratory attempts to infect weevils 



