12 BULLETIN 1117, U. S. DEPARTMENT OF AGRICULTURE. 



cent bore one or two colonies, and that 5 per cent were free from 

 the insects. 



Infected mealybug's were first detected in this grove upon the fruit. 

 Later in the season they were found nearly as abundantly upon the 

 twigs and branches, where, however, they were detected with diffi- 

 culty, owing to the neutral gray color of the fungus, which simulates 

 rather closely the bark of the trees. Upon the grapefruit the dead 

 bugs may occur singly, or more often in groups of four or five, hud- 

 dled together as in life. Surrounding them upon the grapefruit a 

 dark halo V7as often observed, which might easily be confused with 

 the sooty mold that accompanies the insect. This appearance, how- 

 ever, is caused by masses of conidia which are discharged in enor- 

 mous numbers and fall upon the gi-apefruit near or upon one another 

 (PI. I, 21). Dead insects upon the twigs and branches occur more 

 often singly, most abundant in positions near the colony, but often 

 from 5 to 10 feet away, and in such locations, owing to their small 

 size, inconspicuv^us color, and position in the crevicesi of bark, are 

 easily overlooked. 



In studjdng this insect infestation during the period June 13 to 

 August 8. one of the first facts which became apparent was the grad- 

 ual disappearance, week by week, of young insects or crawlers. The 

 total number of insects collected on June 22 and June 29 was some- 

 thing over 1,500, one-third of which were so young that they were 

 discarded for reasons noted below. In later collections the percentage 

 of young ones decreased markedly until, on August 8, but few 3"oung 

 crawlers were observed in the field. It will be observed hj reference 

 to Figure 1 that this period of maximum abundance of young insects 

 is likewise the period in which the percentage of diseased specimens 

 jumped from 18 to 64, and it is to be noted that following this sudden 

 increase in mortality the young or crawler insects became less and less 

 i.umerous. 



In order to obtain definite data regarding the prevalence of the 

 fungus at various periods during the season, so that its work might 

 be measured with some accuracy, the following plan was adopted: 

 Collections were made at approximately weekly intervals, an attempt 

 being made to have them representative of the entire grove. The 

 mealybugs were scraped by a penknife from the grapefruit or twigs 

 to which they were attached and placed in ordinary pasteboard pill 

 boxes. Preferably those grapefruit were chosen upon which large 

 numbers of insects occurred, in order to facilitate the collection, but 

 late in the season it became rather difficult conveniently to collect 

 large numbers, as the colonies Avere decimated and the i/idividuals 

 scattered. In collecting the insects those dead and alive were scraped 

 off indiscriminately, and when taken to the laboratory the crawlers 

 or very small active members were discarded, and those infected with 



