330 



THE AGRICULTURAL NEWS. 



OCTOBKR 19, 1918. 



INSECT NOTES. 



COTTON INSECTS IN ARIZONA. 



The increase in the cultivation of cotton in Arizona 

 daring the past six years has been very considerable, and the 

 insect pests of that crop have naturally been more numerou;- 

 and luoie troublesome with the extension of the area planted 

 in it. The report of Dr. A. W. Morrill, State Ento- 

 mologist, in the Ninth Annual Report of the Arizona Coni- 

 missicn of Agriculture and Horticulture for the year ended 

 June 30, 1917, which has ju.?t been received, contains an 

 interesting section on the pests of cotton observed in Arizona 

 during the year, from which the following notes are taken: — • 



It is seen that during the season under review, and for 

 the past six years the cotton crop has been increasing, while 

 for the previous three years the amount of planting oi fruit 

 trees had greatly decreased. 



The development of the cotton industry is indicated by 

 the following diagram which shows the amount of the annual 

 crop for the State in the years 1912-17. 



A new species of thrips was discovered attacking cotton 

 during 1917. This has been given a manuscript name 

 ( Thrips ■xri'.onensis). It was fairly destructive on a moder- 

 ately large scale, and the statement is made that if this 

 insect continues to appear as a cotton pest it will be necessary 

 to spray for it.s control. 



A small beetle (Myochmns /o!i!;iiiiis. Lee. ) caused serious 

 injury to young cotton in one section, where 500 acres were 

 twice replanted, and the seedlings each time completely 

 destroyed. The cotton had to be abandoned in this area, 

 and another crop was planted. The following is quoted : — 



'In the affected fields not a trace of cotton was to be 

 seen above the ground. Search in the .^oil of the bed row.-i 

 revealed the presence in great numbers of the above 

 apecies. The adults were .>een in many cases still in 

 place on the underground portion of the stems of the 

 decapitated .seedlings, but were also teen commonly feeding 

 on the -iubterranean succulent stems of arrowweed, trailing 

 maiUow. and Bacharii »p. 



'All affected fields were in crop for the fir>t tinie, and 

 prior to clearing the land had(la.'^t season) supported an almost 

 pure growth of arrowweed i P/uc/ua St'rnvti). Owing to the 

 ease which the Myochrous beetles wpre found on the arrow 

 weed stenisit would appear provable that this is the native 

 hr.st of the pest. It is n-HHoniible to .'>upfX>»e then, that 



following the eradication of the arrowweed the beetles trans- 

 ferred their attention to the young, tender cotton plants 

 which were readily at hand.' 



This insect is known to occur on Mesquite {Prosopis 

 julijlora) and has been reported to attack young cotton in 

 California. It is likely that this beetle i.s found throughout 

 all cotton sections of Southern Arizona. (In the West Indies 

 the small beetle Myochrous arma/i/s is known as the corn 

 leat beetle, a minor pest of sugarcane and Indian corn; an 

 account of this insect was given in the Ai:rici'.lliiral \m<s, 

 Vol. XV, p. 26 January 15, IKIO.) 



The light-brown grape-leaf beetle (Cu/aspis druiiiiea,Vah.) 

 which i.s common in the Salt Kiver Valley, ordinarily causing 

 perforations in the leaves of the grape, was found in con- 

 siderable numbers on cotton in 1917. The injury to the 

 leaves was of the same nature as that inflicted on the grape 

 leaves. (Colaspis Jastidiosa, a related insect which occurs in 

 St. Vincent also attacks cotton leaves.) 



The cotton worm {A/al>a»ui argi/hwea, Fab.) was not 

 found in the cotton fields during 1917, making two years in 

 succession when thi».insect was not found. At one time 

 it was feared that the cotton worm would live over the 

 winter in Southern Arizona, and that the infestation would 

 start early in the year. Experience has so far shown that 

 the status of the cotton worm in Arizona is about tha 

 .same as it is in the South Eastern States. It is thought 

 that a moderate infestation of this insect would be very 

 beneficial to the cotton fields of Southern Arizona, where the 

 tendency is toward too rank growth of plants. 



• The cotton boll worm {He lid/ /lis obsqUta, Fab.) was 

 more destructive in the cotton fields during 1917 than at any 

 time since cotton erowing has been taken up on a commercial 

 scale in the Salt Itiver Valley. In one field it was estimated 

 that 30 per cent, of the bolls had been destroye<l by this pest. 

 In another field this insect was responsible for a rather 

 unusual form of injury to cotton. This injury consisted in 

 the attack on the cotton stalk about li inches from the 

 growing tip. The young caterpillars entered the stems at 

 the leaf axils, and tunnelled the stems for some 2 or 3 

 inches, which killed the stalk from the point of attack to the 

 tip. In one section it was estimated that 40 per cent, of the 

 stalks were affected in this manner. This injury is credited 

 to the boll worm, on the evidence of finding one boll larvae in 

 an injured stalk. This specimen was parasitized, several 

 specimen.s of one of the flesh flies {Sarcophaiia licliiis Town.) 

 being reared from it. The total damage was not great from 

 this form of twig boring, and in fact the damage by the boll 

 worm in the Salt Kiver Valley was estimated at less than 5 

 per cent. 



The cotton leaf perforator [/iiUiiilatrix /iiur/ierie/ia, 

 Bu.sck) was more abundant tlian in previous season?. Th^ 

 grasshopper ( Mc/aii<pliis JiJ}i-'r<>iti<iiis) completely destroyed 

 a few acres of cotton, but was quickly and completely checked 

 by the use of poison baits. The cotton stainer {Dysdcnus 

 allnilivcnlri-i, Stal.) mentioned in .-v previous report was not 

 common in 1917, and did no appreciable damage. In the 

 section where these insects were most destructive the previous 

 year, it was with difHculty that a few specimens could be 

 found. Tarnished plant bugs (/i^v^v prtif,-i:sis oi'liiwatus 

 Say and /.. clisiis var. Iies/>ei ua, Kuighti were plentiful and 

 destructive in the Salt River Valley in 1917. In one field 

 it was estimated that 90 per cent, (.i the cottun squares were 

 destroyed, mostly by these insects. This was on July 24, 

 and though the plants were from 4 t.i 5 feet in height very 

 few bolls had set. Soon afterward the bugs left the field, 

 and a snoall crop was produced. 



