410 



THE AGRICULTURAL NEWS. 



Decembee 24, 1909. 



INSECT NOTES. 



NATURAL HISTORY OF INSECTS. 



I'aKT V. Dli-lE^TIOX 

 DKiESTlON. 



The digestive system in insects, in its simplest form, 

 consists of a cylindrical tube, extending in a direct course from 

 the mouth to the anus. In the more specialized insects, the 

 alimentary canal is very modified, being folded and doubled 

 on itself in such a way as to give it a length considerably in 

 excess of the total length of the body. The organs which 

 are concerned with feeding and digestion occupy a very large 

 proportionate part of the entire body cavity, Fig. 4-5 (see 

 Agricultural Nexus, Vol. VIII, p. .378) will give an idea of 

 this. The cross shaded portion is the alimentary canal. Food 

 taken in at the mouth passes by means of the oesophagus, or 

 gullet, to the stomach. Sometimes a croii and gizzard are 

 developed, the crop for storing a portion of food, the gizzard 

 with strong muscles and chitinous ridges and hooks, by means 

 of which the food is reduced to a finer condition before entering 

 the stomach. In certain insects, at least, a larger part of the 

 actual digestive process is carried on in the crop, and in these 

 insects also, the gizzard serves as a strainer through which 

 the finer portions of the food with digestive fluids are carried 

 to the stomach, in which absorption takes place. The stomach 

 is a large digestive region (Fig. 4-5; AL) from which the food 

 passes to the intestine, colon, rectum, and to the anus, where 

 waste and undigested food is voided. The food canal is 

 composed of three sections, the fore-gut, mid-gut and hind-gut, 



The manner of taking food also varies greatly among 

 insects. Certain insects such as grasshoppers eat vegetable 

 food, with biting mouth parts, in both larval and adult stages 

 of their development. Others, .such as j)lant lice and cotton 

 stainers, take plant food by means of .sucking mouth parts 

 also during the whole of the larval and adult life. Others, still, 

 feed with biting mouth parts in the larval stage, and in the 

 adult one either do not feed at all, or get their food by sucking 

 the juices of plant.s and flowers. ^lany butterHies and 

 mot-hs are examples of this. Other examples of the variety 

 of ways of feeding are to be seen in the mos(|uito, the larva 

 of which is a scavenger or predator in stagnant water, while 

 the adult male sucks the juice of fruits and fiowers, and the 

 adult female sucks the blood of animals. Another example 

 is to be found in many bees and wasps, where the same 

 individual possesses mouth parts develo[)ed fur Imtli biting 

 and sucking. 



The manner of feeding has a great infiuence on the 

 development of the food canal. Larvae, with biting mouth 

 parts, which feed on vegetable matter have very large 

 alimentary systems, while predaceous insects have smaller 

 ones and those which .suck the juices of Howers and ]ilants, and 

 the blood of animals, even less. Certain insects which suck 

 their food such as Lepidoptera, Diptera and Henii|)tera, have 

 a development of the gullet which acts as a sucking-pump, 

 by means of which the food is taken n\) and forced back into 

 the stonuich. In bees and ants, the region of the gizzard is 

 occujiied by the honcy-stoniach, into which the noct-ar can be 

 taken and kept separate from tiie actual food of the insect. 

 The nectar or honey can be di.sgorged at will. 



Attached to, or communicating with, the alimentary canal, 

 there arc two or three ditlerent kinds of glands, each kind in 

 pairs or a number of pairs. The salivary glands open into the 

 mouth, and in addition to possessing the function of moisten- 

 ing foods, they are often developed for quite different purjjoses. 

 For instance, the silk glands of the silk-worm and many other 

 ■caterpillar.s, the poison glands of mosquitos and of certain 



.\XD liEi'IlODUCTION 



Hemiptera are salivary glands, or portions of the salivary 

 glands specially developed for the purpose. Other poison 

 glands, scent glands, and glands for many special purposes 

 occur in insects, but quite apart from the digestive system. 

 The kidney tubes, or 'malpighian' tubes, of insects communi- 

 cate with the food canal, at the juncture of the mid-gut with 

 the hind-gut, that is where the stomach and small intestine 

 join. These are often very numerous, and their function is 

 excretory, similar to that of the kidneys in other animals. The 

 waste products are passed into the intestine, and thence 

 voided tiirougli the anus with the undigested food and other 

 waste matter. 



REPRODUCTION. 



Reproduction in insects is sexual, as a general rule, the 

 organs of the two .sexes being borne in separate individuals. 

 Hermaphroditism (the two sexes in one individual) does not 

 occur normally, and it is not known that hermaphrodite 

 insects ever reproduce. The sexual organs are well devel- 

 oped, the testes of the male producing the spermatic fluid, 

 and the ovaries of the female, the eggs. In the female of 

 many species, the ovipositor is developed wiih special refer- 

 ence to the situation in which the eggs are to be laid. 

 Certain grasshoppers are able to force the abdomen into the 

 hard ground; some crickets, thrips, and many other insect.s 

 have saw-like ovipositors, with which cuts are made in the 

 surface of i)lant ti.ssue; piercing ovipositors, of which the 

 stings of the bees, ants, and wasps are good examples, 

 puncture the tissue in which the eggs are to be laid. 



Asexual reproduction occurs in plant lice, during 

 a portion of the year, and in a few other insects. This 

 parthenogenesis, as it is called, is a normal feature in the 

 life-cycle, and the off-spring consists of females. The queen 

 of the honey-bee is able to lay, at will, fertilized egg.s 

 which produce female, and unfertilized eggs which [iroduce 

 male, ins^^cts. Another kind of asexual reproduction some 

 times occurs in insects, known as paedogenesis. The larvae of 

 certain Cecidomyiidae are capable of giving liirth to young, 

 and in another group of small Hies the pupa deposits 

 unfertilized eggs which are capable of hatching. 



The papers on the Natural History of In.sects are con- 

 cluded with the present article. The five parts, taken together, 

 give a comjirehensive view of the vital processes of the 

 in.sects, and also show the differences and likenesses between 

 the insects and the nearest relatives, the Crustacea, the 

 Myriapoda and the Araneida. The structure, growth, senses 

 and circulation, the nervous respiratory and digestive systems 

 and the reproduction of insects have all been treated briefly, 

 but in such a way, it is hoped, as to give the readers of the 

 A'iricultural News a general knowledge of insects. The 

 illustrations, eleven in number, will be found to aid in 

 understanding many of the points. If these arti(;lesare taken 

 in conjuucliiin with those relating to the orders of insects, 

 which afipcared a short time ago, and for which the following 

 references may be consulted, a general outline of West Indian 

 entomology may be had. These references are as follows:^ 

 (Grasshoppers, Vol. VI, p. 218; crickets. Vol. \l, p. 10(i; 

 jjond Hies, Vol. VI, p 2()6; Hemiptera, Vol. \ll, p. 138; 

 Lepidoptera, \o\. VII, p. 234; Coleoptera, \o\. Vil, pp. 250, 

 2(!<); Diptera, Vol. VII, pp. 314, 330, 346; Siphonaptera, 

 \(.l. \TI, p. 34(5; Hymenoptera, Vol. VIII, p. 234. 



