250 



THE AGRICULTURAL NEWS. 



August 11, 1917, 



INSECT NOTES. 



WHITE GRUBS INJURIOUS TO SUGAR- 

 CANE IN PORTO RICO 



In the last number of the Agricultural A'tirs an account 

 ■was given of the life-cycle and habits of a typical species of 

 hard back beetle as studied by Mr. E. G. Snjyth in Porto 

 Rico. In ihe present issue it is proposed to refer briefly to 

 the principal natural ei emies of hard back grubs, as observed 

 by Mr, Smyth. 



The natural enemies of hard back grubs— or white 

 «rubs as thty are often called - are grouped under three 

 «lasscs, namely, animals (including birds and lizards), insects 

 {including mites and worms) and plants (fungus and 

 ■bacterial). 



ANIMAL ENEMIES OF HAED BACK ORUBS IN PORTO EICO. 



Field mice and rata are mentioned as possibly account- 

 ing for a few specimens of grubs, but these cannot be con- 

 sidered of any great importance. An attempt was made by 

 OLe of the sugar estates to introduce hedgehogs from Europe 

 a few years ago, but owing to the unfavourable surroundings 

 in which they were liberated, the) did not become established. 

 These hedgehog.s ate hard backs greedily when fed to them in 

 confinement, but they were not observed to burrow deep 

 enough into the soil to get at tlie grubs, and it is question- 

 able whether they would have been of any value as an 

 agency of control had they become established 



Insect eating lizards are very abundant in Porto Piico, 

 but most of these, belonging to the genus Anolis, are too 

 small to feed on the Urger hard backs. Further, they are 

 at woik only during the day, usually on trees, whereas the 

 hard backs hide in the ground during the day, only coming 

 out at nightfall. 



A large burrowing ground lizard (Ameiva exul) is 

 mentioned as being a probible feeder on hard back beetles 

 and prubs. 



It may le mentioned that the ^enus Ameiva has a wide 

 ran e throughout the West Indies, but the several species 

 are quite localized, many of them being confined to a single 

 island. Th s species, i^niei'a ««/, has a wider range than 

 many of the other species of this genus being found upon 

 Porto Rico, Vieques, St. Thomas, St. Croix, St. John, and 

 Water Island. (Barbour, Tbos. Mem. Mus. Comp. Zool. 

 Haivard. Vol. XLIV, No. i, 1914.) 



Birds constitute an important factor in the control of 

 hard back grubs in Porto Rio. The three most important bird 

 enemies are: (1) the Porto Rican blackbird or 'inosambique' 

 (I/'Joquifcatvs hrackyp'erux): {i) the bare-legged owl ((?^»i- 

 nas o nudipes iivdipes\ and (.'5) the little blue heron (Florida 

 caenilea caerulefceiis.) The mangrove cuckoo {Coccy-.us minor 

 ■ntii'iies) is also mentioned in this connexion. 



Tiie blackbird is regiidcd a-^ the most important of these 

 enemies because it is very abundant in the districts of Porto 

 JRico where the hard-back yrubs aie most injurions, namely, 

 in I he arid coast regions. It was found by observation and 

 count that over 90 per cent, of ihe grubs exposed by the 

 plouiihs are pickt-d up by these birds Mr. Smyth goes on 

 to say that 'when it is considered that a bird is able to 

 coi.sume more than the ec|uivalrnt of its own weight of food 

 in twenty-four hours, and that blackbirds during the plough- 

 ing season of five to six months subsist almcst wholly upon 

 grubs, one may appreciate the vast numbers of grubs that 

 they consume,' 



INSECT ENEMIES OF HARD-BACK GRUBS IN rOETO EICO. 



Mr. Smyth has found that among the insect enemies of 

 mt'lolonthid larvae and related hardback grubs there are at 

 least nine species known to occur in Porto Rico Six of 

 these are Hymenoptera, belonging to the wasp family 

 Scoliidae, iwo areTacninid files, and one is an Elaterid beetle. 

 At present very little is known about the parasites of these 

 grubs in Porto Rico. 



Of the nine species mentioned above 'there is direct 

 evidence of only one of them destroying the grubs of 

 Phyllophaga (Lachnosterna) This the Elaterid beetle 

 {I'yrophoruf, liimincsus), larvae of which have been fed upon 

 Phyllophaga grub.s for long periods in confinement in the 

 insectary.' 



It may be mentioned that this beetle is closely 

 related to the luminous night flying beetle Pyrophorus 

 noctilucus, which occurs in .some of these islands. This beetle 

 is much larger and gives a much brighter light than the 

 smaller 'fire fly', belonging to the coleopterous family Lampy- 

 ridae. Very little is known of the hibits of the larva of 

 noctiliicvs. 



No definite statements can be made as to the value of 

 P. luminosus larvae in ihe control of hard-back larvae under 

 field conditions in Porto Rico. This species is apparently 

 confined to the north and west coasts. 



The scoliid wasp Campsomeris dorsata is known to 

 parasitize the common black hard back (Ligyrus tumulosus) 

 abundantly at all seasons, but there are so far no definite 

 records of its attacking Phyllophaga grubs in Porto Ricj. 



This species of Carap.soraeris (Dielis) is the common 

 parasite of Ligyrus in Barbado.s, and has occasionally been 

 found parasitizing Phytalwi smithi. 



Mr. Smyth mentions that of thousands of Phyllophaga 

 grubs collected in cane fields and examined by him. i ot one 

 has ever been found parasitized by a scoliid egg or larva. 



It would appear that the most important parisitic enemies 

 of these Phyllophaga species in Porto Rico are the two Tachi- 

 nid flii s {Cryptomeigenia aurifacies) and Kulrixoides jonesii. 

 Both of these flies are parasites of the adults, and Mr. Smyth 

 ■says that further oSservaiions may possibly .•■how that these 

 parasitic flies lay their eggs on the beetles at the time that 

 thela'terare in iting just before nigh' fall. The number of 

 fly pupae found in one dead beetle varies from two to nine, 

 and is iisnally from four to six. 



It is further stated that infested beetles that have died 

 as a result of this parasitism are always found in their burrows 

 underground. 



Like the Pyrophorus beetle mentioned above, these fly 

 parasites appear to oe found only in the more humid 

 section of the n'rlh and west coasts, and Mr. Smyth 

 thinks that the presence ot these three enemies may help to 

 explain why white giubs are less injurious in the.se regions 

 than on the dry south coast where there are few or no 

 Tachinid parasites or Pyrophorus beetles. 



INTl'.ODUCTION OF PARASITE.-^ INTO POETO RICO. 



After it was found that the native parasites of white 

 grubs wore tjuite insufficient to prevent the continual increase 

 of these pests in Porto Rico, the introduction of parasites 

 from outside was taken in hand. 



This Work was begun in 1911 by Mr. D. L. van Dine, 

 at that time Entomologist of the Porto lUco Sugar Producers' 

 Experiment Station. A special collaborator was employed 

 to collect living white grub parasites, or parasite cocoons, in 

 the L^nited States, and ship them to Porto Rico in living 

 condition. This work was carried on from June 1911 till 

 October 1914, first by Mr. C. E. Hood, and later by 

 Mr G. N. VVolcott. 



