69 



The Cactus Weevils, Gerstwckeria, spp. 



This group of weevils, which feed exclusively 

 on cacti, has received the special attention of Mr. 

 \\-. D. Pierce, of the Bureau of Entomology 

 (1907, 1911). The genus consists of about 

 twenty-two species— eleven in the United States 

 pnd eleven in Mexico and Central America. 



The adults feed more or less superficially 

 here and there on the joints, whilst the larvre live 

 within them.* The latter do not cause much 

 injury, as they derive their food-supply from the 

 neighbourhood immediately surrounding the spot 

 where they were hatched, the larva undergoing its 

 transformation into the adult within the cavity 

 which it has made in the segment. They do not 

 produce any serious effect on the attacked joint, 

 .IS a callus is formed by the plant tissue. In the 

 case of the larva of G. porosa, which breeds in 

 the flat portion of the joint, the injury may extend 

 from one surface to the other, and then a " shot* 

 hole" effect may be produced. At times, the 

 injury may be aggravated by the presence of 

 (scavengers, more especially files, but this does not 

 appear to happen often. Hibernation takes place 

 under fallen joints (Pierce). 



6. {Philopuntia) porosa, Le Conte. — G. 

 porosa is a wide-spread species, being recorded 

 from Colorado to Arizona, Texas, and New 

 Mexico (C.I., p. 30, Pierce, 1911, p. i65). Eggs 

 are deposited singly in or on the surface, the larva 

 on hatching living within the flat portion of the 

 segment. Eventually the grub makes a small 

 oval cocoon, about 8 mm. long, from aggluti- 

 nated fragments of excreta, where it undergoes 

 its transformation. The injuries caused by the 

 insect or its larva were found by the Commission 

 on 0. lindheimeri at Laredo and San Antonio, 

 while at Wallace, Western Kansas, injuries 

 c-imilar to those caused by the adult weevils 'vvere 

 noted. In the last-named district the species was 

 probably either G. porosa or G. iasalls, judging 

 from its known distribution. Adults of G. porosa 

 Mvre taken near Tucson, Arizona, on 0. arizonica, 

 0. fulgida, 0. spiiiosior, 0. mammillata, and 0. 

 arbuscula. Mr. Pierce, who identified the speci- 

 mens, mentioned that this species was greatly 

 parasitised by undetermined hymenoptera, a 

 statement which we were able to confirm by per- 

 sonal observations at Laredo, Texas, where several 

 hymenopterous larvas were collected from a cocoon 

 of this species. 



G. (Philoptmtia) nohilis, Le ■ Conte. — This 

 species is rather larger than the former, and mea- 

 sures about 7 mm. in length. Its eggs are deposited 

 singly at the base of an areole preferably on the 

 upper edge of a joint. Hence the larval injuries 

 are more or less terminal, and associated with 

 them there is, in addition to the insect excreta, 

 a black exudation of the hardened mucilage of 

 the plant. The latter is said (C.I., p. 30) to 

 interfere with the development of new growth. 

 The blackening is due to the growth of fungi. 



The adult and larval stages were seen by 

 us near Sinton attacking 0. lindheimeri and 

 related species. The adult is black, clothed with 

 brownish-coloured scales and with five conspicu- 

 ous patches of white scales. The elytra have 



* This remark doeg not apply to O. hmhhardi according 

 to our observations, 



seven costas. The larva is a small, white, oblong, 

 tootless grub with a glossy brown head and with 

 transverse folds or wrinkles on each body-seg- 

 ment, there being isolated short brown hairs on 

 each side of the last two segments. In the Bul- 

 letin on Cactus Insects (p. 43, and Pierce, 1911, 

 p. 164) the host is quoted as 0. engelmanni, and 

 tile distribution given as Southern and Eastern 

 Texas (p. 30). Since 0. engelmanni does not 

 occur in those districts, the name evidently refers 

 to 0. lindheimeri and its numerous allied varie- 

 ties and species commonly met with in that 

 region. It is figured in C.I., p. 30, fig. 3. 



G. (Opuntiaphila) hublardi, Le Conte.*— In 

 a conversation, Mr. E. Schwarz referred to 

 extensive destruction of the common Opuntia at 

 Lake Worth and Crescent City in Florida, and 

 Selma, Alabama, which he said was caused 

 by this species, whose larva breeds in the joints. 

 The host-plant is recorded by Le Conte as 0. 

 vulgaris (C.I., p. 30). In the Bulletin on Cactus 

 Insects (pp. 30, 43) it is mentioned that the 

 weevil appeared to. follow the work of a moth, 

 Meliiara prodenialis. 



A visit was paid to Florida, and the beetle 

 found on prickly-pears, probably 0. austrina at 

 West Palm Beach. The attacks of the Melitara and 

 G. hubbardi were seen to cause serious injury to 

 infested plants, some of them having been killed. 

 The sparse distribution of the Opuntias in the 

 locality may have been occasioned by insect 

 devastation. In all observed cases the moth and 

 the weevil were associated. 



* The insect is a very stout-bodied beetle, 8 mm. long 

 and nearly 6 mm. broad, and when seen from above has 

 an ovoid profile. It is of a general black colour with 

 numerous brown scales, the small areas on the surface 

 where these are absent appearing as black points. 

 Commonly individuals appear almost black, owing to the 

 loss of their white scales by abrasion. Conspicuous 

 patches of white chalk-like scales are disposed as follows : — 

 One pointed above on forehead and extending downwards 

 between the eyes ; an elongated one on each shoiolder 

 uniting with the suture, the two forming the commence- 

 ment of the firstmentioned ; a sinuate band crossing the 

 elytra at their declivity ; and a band also on their hinder 

 slope. The femora, tibia, and tarsi of the legs are variously 

 spotted with patches of these white scales. The elytra are 

 coarsely ribbed, the interstices containing large punctures 

 and transverse rings. The rostrum is curved, and when 

 folded under the insect reaches just beyond the anterior 

 coxa. The thorax is much narrowed and coarsely punctured, 

 and has a single longitudinal dorsal keel occupying the 

 anterior two-fifths. 



The eggs are laid singly each in a perforation made 

 in the tissue of the joint. These injuries, arising from 

 oviposition, result in the formation of a well-defined grey 

 circular spot. The egg is smooth and oval, of a dull 

 yellowish-white colour, and measures 2 mm. in length by 

 about 1 mm. in breadth. 



The larva is an elongate, transversely wrinkled, footless 

 grub with a glossy brown head and pioeous mandibles. 

 There are three rows of low conical tubercles on each side 

 below the level of the spiracles. Small solitary brown 

 hairs occur on the hinder segments. The larva feeds 

 within the joints, and appears to be able to carry on its 

 operations in moist, discoloured, and even semi-fluid 

 broken-down tissues. 



The cocoon is a pale yellowish oval body 15 mm. long 

 by 10 mm. wide, of firm consistency, having a rough 

 anterior end, and composed of dry plant tissues within 

 which pupation takes place usually. It is sometunes dark- 

 coloured, a circumstance that is due to the larva having 

 fed on the dark disorganised tissue of the host^plant, as it 

 commonly does. Again, when it has been formed on the 

 grotmd, it may have fine particles of sand interwoven uj 

 its walls, and be accordingly of a hard consistency. 



