250 



THE AGRICULTUKAL NEWS, 



Ai'.irsT lu, 1918. 



INSECT NOTES. 



FEEDING HABITS OF THE PARASITES 

 OF HARDBACK GRUBS. 



Frequent ^efel■enco^ liavt.- been made ia previou.s issiie.s 

 of the A,i;ri(Ultiiral 'Kavs and otlier publications of thi.x 

 Department to the occurrence of the grubs of various specie.-; 

 of beetles which live in the soil and attack the roots of 

 cultivated and other plants, and the reports and tiuUetins 

 of other I>epartuients of Agriculture and E.'cperinieut Stations 

 often include accounts of these insects. Some of these 

 insect.^ have long been known as pests, while others have more 

 recently attracted attention on account of their depredations. 

 In recent years, soil-inhabiting grubs have become a much 

 more prominent feature in agricultural practices in many 

 parts of the world, both in tropical and temperate countries, 

 and, at the same time, the parasites which attack them have 

 come t<i be regarded with greater interest. Any parasite which 

 attacks a pe.Ht of agricultural crops is of importance and 

 interest, because of the likelihood that it may be a factor in 

 limiting the numbers ot the pest to such a degree as to 

 prevent its causing serious damage to the plants, and conse- 

 ^juent loss in the amount of crop obtained. 



Several species of beetles, which in the larval stage of 

 development attack the roots of plants, occur in the West 

 Indies. Oue of these, the brown hard back (^Phy talus smitlii), 

 which is known as a minor pest of sugar-cane in Barbado.s, 

 and is recorded as occurring in Trinidad and Brazil, has, 

 since 1^*11, come into great prominence as a most serious 

 pest of sugar-cane in .Mauritius. 



It is believed th it this insecc was introduced into 

 Mauritius not long before its discovery therein 1911. Its 

 remarkable increase in numbers in that colony was without 

 doubt due to its having been removed from the association 

 with its natural enemies, one of which is now known to be 

 the Scoliid wasp {Tipliia pai-allcUi), which is an active and 

 efficient parasite of the beetle larva. 



As the result of careful observation. Mr. VV. Nowell then 

 Assistant Superintendent, Birbados Department of Agricul 

 ture, discovered in 1911 the relationship of host and parasite 

 which exists between the tsrubs of the brown hard back and 

 the Tiphia wasp, and published an account, which is to be 

 found in the W'ist Indian Jhilltlin (\'ol. XV, p. 149) of this 

 and a related parasitic wasp {Ciiiiipsumeris liorsa/i). 



From this account it ap])ears that the adult female 

 Tiphia, having founrl a suitable grub of Pbytalus, stings it, 

 thus rendering it quiescent or paralyzed. An egg is then 

 laid ('n and securely attached to the surface of the grub's 

 br'-dy. In a few days the egg hatches, and the young parasite 

 grub. Hind and footless, attaches itself by means of its mouth 

 parts at the point where the egg was attached, ,>,nd proceeds 

 tc .~uck out the contents of the beetle grub's body, this being 

 completed at the lime when the parasite has attained its full 

 growth. The period of pupation follows, and in due course 

 the adult [)arasite wasp issues forth. 



This seems to be the usual method of feeding, during the 

 larval stage by the several parasites of this grf>up of wa.-^ps 

 on the grubs of beetles. 



The adults of some of these insects are visitors to flowers, 

 feeding on the nectar which they find there. Campsomin'.-. 

 dor ata^ for example, is a very freijuent visitor to flowers: 

 on tilt other hand, Tiphia paiallila is not recorded as 

 visiting Howei-- at all, but is known to feed on the secretion.s 

 of plant lice, and, in captivity, on sugary liquids and honey. 



Soon after the i arasili.-m of Tiphia on the larvae of 

 Phytalus was e>tabii3hed, the (iovernment of JLuiritius 

 attempted through the cooperation of the lUrbados Govern- 

 ment to introduce the parasite into Mauritius, with the object 

 of establishing it for the purpose of controlling the epidemic 

 of Phytalus attack. A paper entitled 'The Importation of 

 Tiphia Parallela into Mauritius . by Mr. 1). d'Kmmerez de 

 Charmoy, Government Entomologist, Mauritius {Bii/kti/i 

 E'ilomoh\^ical Rcs-Huxh^ August 1917), gives a good account 

 of the trials that have been made. 



Five consigcments of parasites and parasitized grubs 

 were sent from Barbados to Mauritius- three in 1913, one 

 in 1914, and one in 1915. Of these only one was successful 

 from the point of view of living Tiphias arriving in Mauritius 

 in condition to live and breed. 



At the end of the year 1915, two couples of this insect 

 were liberated near the Botanic Gardens, and two other 

 couples escaped from the insectiry at the Botanic Gardens. 

 In May 1916, parasitized beetle larvae were found in 

 the same field where the Tiphias were liberated about 

 six nnnths before, and later many adult Tiphias have^been 

 observed in the same vicinity. lu May 1917, Tiphias were 

 to be found in thousands on the estates near the Botanic 

 Gardens. 



The success of this importation seems to have depended 

 altogether on the ability of the freed Tiphia adults to find 

 suitable food during the period of mating and egg-laying. 

 From this emerges a very interesting point, one which may 

 also have a bearing on the local distribution of these insects 

 in the West Indies. 



It has been stated ia the course of this article that 

 adult Tiphias in Barbados feed on the sweetish secretions of 

 aphides. In Mauritiui, aphides appear only at a certain time 

 of the year, and then are rapidly destroyed by their natural 

 enemies. From this it was feared that the first Tiphias to 

 gain their freedom in Mauritius would not be able to live and 

 propagate on account of lack of .suitable food, but they 

 appear to have made up for this deficiency 'by having re- 

 course to the sweetish content of the vesicular hairs of Card/a 

 iii/crriip/'t. This plant is a native of British Guiana, which 

 was introduced about fifteen years ago: it is now a regular 

 pest and infests all uncultivated fields.' 



From reference to Floras of the West Indies, it appears 

 that Cordia i/i/crnip/a is a variety of Conlia cvUndrosfac/iya, 

 the common black sage of Barbados and other islands. It 

 seems certain that it is the chance introduction and establish- 

 ment of this plant that has made possible the successful im- 

 port»tion of Tiphia parallela into Mauritius. 



In a report by the same author (Mr. d'l'^nmerez de 

 (.Jharmoy) dated December 1917, on the Importation of 

 Scoliid Wasps from Madagascar for the purpose of controlling 

 the large soil-inhabiting, root-feeding grub, Orwics tarandm 

 the following statements occur in numbers 4 and •'> of the 

 summary of general conclusions in relation to Scolia 

 (>r\(topha;j;a: — 



'4. In attempting the introduction of Sudia orwlopha^'a 

 in Mauritius for the purpose of parasitizing Orvilcs tarandtis 

 due regard must be had to the feeding habits of the adult 

 insect, and provision be made of an adequate supply of suit- 

 able nectar-bearing flowering plants in the localities in which 

 it is desired tliej' should increa.se. 



'5. The most suitable plants for the purpose appear to 

 be Cordia interrnpta and Uirna lam: n/osa, and it is desir- 

 able that these plants should be established on the borders 

 and in the vicinity of cane field.-^ in the districts in which 

 introduction of the parasite is to be eSfected.' 



