40 DITING AND NOXIOUS INSECTS OTHER THAN MOSQUITOES 



on all flio liirti-rcnt apocies (of aphis) and sonic of tlicni, at least, have funf,'us iliseasps as 

 well to i-ontfud against. Natural clucks of other kimls arc still nioiv potent in oft-setting 

 their marvellous reproduetive powers; thus, myriads perish on the citrus trees with the 

 hardening of the young wood, and violent rains dash other myriads to the ground, never to 

 regain their food plants. The most eonspieuous, as well as the most important in many 

 cases, of the insect enemies are the la<ly-l)irds. lint no species of lady-bird can increase in 

 nunihers to compare with an aphis. Few lady-birds have more than three or four generations 

 a year in even warm climates whilst aphides are often grandparents before their first month 

 of existence is tinished. Thus it comes about that when conditions favour the increase 

 of an aphis and it has even a short start of a ladv-liinl enemy, the plant infested may be 

 severely injured before the aphis is suppressed. To cite a common example: A species of 

 aphis (Xectaropltitm /lixi) sometimes tiiids nur succt-pca plants early in tlic spring, and, say, 

 for a week has undisturbeil possession. Tiien the infestation is discovereil by a wandering 

 lady-bird on the search for just such an occurrence, and she at once proceeds to avail herself 

 of it. feeding voraciously her.self and laying eggs that her progeny may share the feast. 

 The eggs hatch in about a week ami tiun a swanii (jf liuii^'ry iarv;e slay the helpless lice right 

 and left. Doing their best, however, and aided by other lady-birds which have been attracteil 

 to the scene, they cannot even dispose of the increase. In a few weeks the larv.e turn to pupaj 

 and then to adults. A second generation of larvie is shortly produced and then the ajdiis is 

 quickly overcome. Sometimes, of course, the apliis is overcome more speedilv and sometimes 

 less so ; from the beginning almost there was no doubt as to ultinuite sup|)ression. Th(! 

 lady-bird larvie wander about when their food supply is exhausted, but not having wings they 

 do not get very far ; some eventually find food and live to propagate, but the va«t majority 

 die of starvation or full virtinis to tlicir caiinabiilistic lirotlicrs or to oilier foes. For weeks 

 at a time there may be practically no aphis of any kind in tiic locality and then the lady-birds 

 become fewer and fewer, so that when aphides begin to appear again there are very few 

 lady-birds about to find them. Other enemies of the aphis kind stiffer similarly. These facts 

 render it somewhat doubtful tliat the injuries to plants from aphides in general could be much 

 lessened by importing new species of lady-birds since the new-comers would suffer from the 

 same disabilities as our native kinds. Still, it is possible that the conditions might be 

 somewhat bettered if the imported species propagated more rapidly than the natives, if they 

 started to fee<l a few days earlier in the spring, or kept at work through our niibl winters 

 when there was food ; likewise if they had a wider range of foods that would enable a greater 

 proportion of them to live through their famine perio<ls, or if they possessed greater vitality 

 that would assist in carrying them through." 



These interesting notes present the somewhat complex iiroliicms which have to be faced 

 when tackling the question of aphis destruction in a practical manner. Moreover, it requires 

 care and skill to rear captive lady-birds and it is diliicult to feed them. They are liable to 

 bacterial infection and doubtless many would perish or ever they reached the Sudan. Still, 

 this seems the oidy likely way of combating the A/>/iis minilii. and if successful, both the 

 agriculturist ami the treasury would greatly benefit. 



In this connection I may record the discovery of a third species of preilatory huly-bird 

 which is described by Mr. Theobald (p. 93). 



The only real effort to cope with the aphis in the Sudan appears to have been made by 

 5Ir. f'orbyn on the ]\\w Nile. He employed petroleum washes at an early stage of infestation 

 and apparently with great success, as he states that the dura crop on the Government farm 



