DISTRIBUTION OF INJURIOUS INSECTS 15 



we may note that in some countries — Malaya, for instance — 

 they so far only occur in the ports and along the littoral. 

 Their further advance inland is more gradual. This takes place 

 mainly along the river courses by boats and along the rail tracts. 

 In both river steamers and trains we often find this mosquito 

 in numbers. Not only by artificial means do we get a most 

 annoying insect spread, but there is the concomitant danger of 

 yellow fever as long as we have the insect, that carries it, present. 

 Luckily this mosquito is found breeding almost exclusively in 

 and around houses and dwelling-places, and so can easily be 

 destroyed. 



In a similar way the Brown Household Mosquito {Culex 

 fatigans, Wiedemann) seems to have been distributed. Skuse 

 tells us that its advance inland in Australia has followed the 

 opening of the railways. We know, as with the former insect, 

 that it is often a fellow-passenger on board ship. Both these 

 insects have nevertheless their finality of distribution, and we 

 find that they will not live if they reach farther than somewhere 

 near 48° north and south of the Equator (under normal con- 

 ditions). They have both spread outwards from the warmer 

 regions. 



On the other hand, by similar artificial means the Brown 

 Spotted-Mosquito {Theobaldinella spathipalpis, Rondani) of 

 Southern Europe has spread in the reverse way, and we now 

 find it at Khartoum and at the Cape. We know of no records 

 until the last few years of it at the Cape, its advent being 

 probably due to the large number of transports running there 

 during the recent war. This species is found in abundance at 

 Teneriff'e and other islands on the way to Africa. 



The instances quoted here are merely a few which show from 

 recent observations how insect enemies may and have been 

 distributed from country to country, and how they may or may 

 not increase to such an extent that they even out-rival the 

 damage they do in their native lands. To repeat once more, 

 "One can never prophesy how an introduced insect may act 

 in its new home." It is therefore essential to the well-being of 

 mankind that this insect dispersal by artificial means should 

 be dealt with universally, in regard to those pests which attack 

 farm and garden produce, stores, stock, and man, to save further 

 loss and danger. 



