>.50 



THE AGRICCLTURAL NEWS, 



August 3, 1912. 



INSECT NOTES. 



AN ACCOUNT OF TWIG GIRDLERS. 



In a recent nunilier of Science (Vol. XXXV, !XIay 3, 

 1912, p. 714) a meeting of the St Louis Academy of ScieBce 

 is reported. Among the papers presented was one entitled 

 A Grove of Deformed Tree.s, by I)r. J. I!. Terry. 



Since information concerviing the insect mentioned as 

 causing the injury -wliich resulted in the deformities of 

 the trees is likely to be of interest to readers of the Agri- 

 tultiirul Netvs, the account of the paper as given in Science 

 is reprinted herewith. 



'A grove of four or five hundred small persimmon trees 

 in St. Louis County has suffered from the ravages of a beetle 

 which has Iseen identified as Oncideres cingidata. Limbs 

 varying in diameter from 5 to 15 mm. are girdled, and the 

 ends fall to the ground. All the trees, old and young, have 

 been attacked. The girdling is done in the fall, mainl)- in 

 September and October. During this time the larger trees 

 pre.^ent scores of branches bearing dead leaves, and the ground 

 is strewn with fallen branches often laden with fruit. There 

 is no tree in the grove that does not present a crooked trunk 

 ;ind limbs. The deformities in some cases are extreme. 

 Most of the trees are as a consequence dwarfed, although 

 able to make .some advance in growth. Some trees only 

 a metre and a half tall bore fruit in 1911. 



'A few beetles have been observed working. The cut was 

 begun on the upper side of the branch and was made 

 3-4 mm. wide and about 3 mm. deep. Most of the limbs 

 fall, probably within a few days after the girdling. A small 

 proportion remains throughout the following winter. On 

 every severed branch, near the distal ends of the twigs, one or 

 more small deep excoriations of the bark were found. That 

 the beetle makes similar abrasions of the bark of twigs of the 

 honey locust is known from ol>servation of < Jncideres in cap- 

 tivity. Limbs recovered from the ground in winter in some 

 cases presented no evidence of the propagation of the beetle, 

 whereas in others more or less of the wood had been destroyed 

 under the bark along one sice of the branch extended frciu 

 the distal end prcximally. The cavity never quite reached the 

 proximal severed end. Larvae, which are now being studied, 

 were discovered in some of the tunnels.' 



In the genus Oncideres are to be found species of lor.g- 

 horned insects which are known as girdlers. I<r. Sharp, in 

 the Cambridge Natural History (Insects, Part II, p. 286) 

 states the characteristic habit of the genus in the following 

 words: — 



'The species of the American genus Oncideres are called 

 girdlers because the parent beetle, after laying an egg in 

 a small branch, girdles this round with a deep incision, so 

 that the portion containing the larva sooner or later falls to 

 the ground.' 



In certain of the West Indian islands the genus is 

 represented by Oncideres amputator, Fabr., which in St. Lucia 

 is reported as attacking poia doux (Iin/a laurina), and in 

 St. Vincent, Inga dulcis. West Indian ebony {Albizzia Lelheh) 

 and cacao. Many persons in the West Indies believe that the 

 girdling or pruning of twigs of trees is done by the Hercules 

 beetle which, they say, clasps the two great horns, one pro- 

 jecting from the head and one from the thorax, around 

 a twig and then by means of the wings swings round and 

 round the twig until it is cut ofi; by the action of the horns. 



An examination of the horns of the Hercules beetle 

 will suggest at once the difficulty which the insect would 

 have in' cutting oiSf a twig with such smooth-surfaced instru- 

 ments. It is more probable that all the pruning of trees in 



the West Indies which has been ascribed to the Hercules 

 beetle his been done by the girdler, 0. amputator, or l)y 

 a similar insect with like habits. 



The Hercules beetle is one of the largest of beetles,, 

 measuring G or 7 inches in length, including the horns, which 

 project forward one above the other; the lower one from the 

 head has an upward curve; the upper one from the thorax has 

 a downward curve. The inner surfaces of these curves are 

 lined with short bristles, brown to reddish in colour. The 

 girdler is a much smaller insect, only about f-inch in length 

 and narrow in proportion. The ground colour is dark brown, 

 almost black; the surface is overlaid with fine greyi.sh scales, 

 among which are scattered small patches of reddish or orange- 

 coloured scales. The antennae are long and slender, the 

 head is broad and pointed dow^nwards, the thorax has»- 

 a small projection on each side, and the shoulders or bases of 

 the wing covers are pronounced. 



NATURAL CONTROL OF THE CITRUS 

 MEALY-BUG IN CALIFORNIA. 



In an article published in \h.e Monthli/ Bulletin nf the 

 California State Coir/missioii of Horticulture ior Jfay, 1912, 

 Mr. A. S. Hoyt, Deputy Quarantine Officer, at Los Angeles, 

 discusses the degree of control which has been attained 

 over the citrus mealy-bug, Px' ud/y or. us citri, in one district- 

 in San Diego, California. 



In this district there are certain citrus groves which for 

 nine years have not been sprayed or fumigated, entire 

 dependence, having been placed on the action of natural 

 enemies for the control of the pest. During this time these 

 estates have principally had to contend with the citrus mealy- 

 bug, and the chief insect natural enemies have been two 

 lady-birds which in both larval and adult stages prey upoa 

 the mealybug in all its stages of development. 



These lady-birds are Cri/ptolaemus ynontrouzieri and 

 C ryptoiionus orbiculus, the former of the two being con- 

 sidered the more important. 



At the time of the introduction of these two ladybirds 

 the mealy-bugs were very abundant, and consequently the 

 predaceous insects made a remarkably rapid increase as- 

 a direct result of an abundant food-supply. After the mealy- 

 bugs had been almost entirely destroyed by the lady-birda, 

 these beneficial insects died from want of food. Theu 

 a very different aspect of the case presented itself: the mealy- 

 bugs developed rapidly — much more rapidly in fact than the 

 ladybirds — until after a certain time the beneficial insects 

 again became tuost numerous and assumed control. 



Thus through the whole period of nine years, there have 

 been periods of abundance of mealy- bug, when the lady-birds 

 were few in number, succeeded by periods of abundance of 

 lady-birds and a decreasing number of mealy-bugs. 



The writer of the article states that in groves where 

 this method has been followed exclusively, trees and fruit 

 have been, at times at least, covered by b'ack blight and 

 there has been a loss of fruit bearing wood in the interior of 

 the trees. 



In the concluding paragraph, the writer gives it as hi.% 

 opinion that the best way to ensure clean fruit and healthy 

 trees, and at the same time to employ as far as possible pre- 

 daceous insects, is to spray for mealybug only such trees as 

 are badly infested and in which the lady-birds have failed to- 

 aUbdue the pests, leaving to the care of these insects the tree* 

 in which they are actively at work and making every attempt- 

 to fo.ster these beneficial insects and promote their work. 



