1988 . The Journal of Arachnology 16 :272 percentage of biological control may then be supplemented with selectiv e insecticides (insect growth regulators) to attain the desired degree of suppression . Therefore, careful manipulation of several components is needed to enhance th e beneficial fauna in the highly-disturbed commercial Christmas tre e agroecosystems.

LITERATURE CITED

Bosworth, A . B., H. G . Raney, R . D. Eickenbary and N . W. Flora . 1970 . Nocturnal observations of in Loblolly pines at Haworth, Oklahoma . J. Econ . Entomol ., 63 :297-298. Bosworth, A . B ., H . G . Raney, E . D . Sturgeon, R . D . Morrison and R . ]D. Eickenbary. 1971 . Population trends and location of spiders in loblolly pines, with notes of predation on th e Rhyacionia complex (Lepidoptera : Olethreutidae) . Ann . Entomol . Soc. America, 64:864-870. Eickenbary, R. D . and R . C . Fox. 1968 . predators of the Nantucket pine tip moth, Rhyacionia frustrana. Ann. Entomol . Soc . America, 61 :1218-1221 . Greenslade, P. J. M . 1964. Pitfall trapping as a method of studying populations of Carabidae (Coleoptera) . J. Anim. Ecol., 33 :301-310 . Juillet, J . A. 1961 . Observations on arthropod predators of the European pine shoot moth , Rhyacionia buoliana (Schiff) (Lepidoptera : Olethreutidae), in Ontario . Canadian Entomol ., 93 :195 - 198 . Kaston, B . J. 1978. How to Know the Spiders . 3rd ed . Wm. C. Brown Co . Publ., Dubuque, 272 pp . Ohmart, C. P. and W. G . Voight. 1981 . Arthropod communities in the crowns of the natural an d planted stands of Pinus radiata (Monterey pine) in California . Canadian Entomol ., 113 :673-684 . Scriven, G . T. and R. F. Luck. 1978 . Natural enemy promises control of Nantucket pine tip moth . California Ag ., 32 :19-20. Scriven, G . T. and R . F. Luck . 1981 . Biological control of an introduced Monterey pine pest . Gold . Gard ., 49 :9-10 .

A. D. All, Cooperative Extension, Department of Entomology, University o f California, Riverside, CA 92521-0314 USA ; and Janet S. Hartin, University of California Cooperative Extension, 777 East Rialto Avenue, San Bernardino, C A 92415-0730 USA .

Manuscript received October 1987, revised February 1988 .

PREY HANDLING AND FOOD EXTRACTIO N BY THE TRIANGLE-WEB SPIDE R CAVATUS ()

Triangle-web spiders, (Hentz), emerge from egg sacs as second instars, begin constructing prey-capture webs when they enter the third stadium , and mature as sixth instars (Opell 1982) . During an earlier laboratory rearing study of developmental rates and web production (Opell 1982), I also collecte d prey remains and recorded prey handling times . Here, I describe the prey necessary for the maturation of H. cavatus, trace developmental changes in it s prey handling times and prey extraction rates, and evaluate the feeding efficiencies of each of its instars . 1988 . The Journal of Arachnology 16 :273

Table 1.-Prey consumption and prey extraction during Hyptiotes cavatus development.

PREY PREY EXTRACTIO N CONSUMPTION (mg dry weight) No . Mean No . SD No . Mean Extraction Stadiu m INSTAR Spiders Prey/Spider Prey Per Fly Tota l 3rd 21 3.9 1 .8 72 0.08 0 .32 4th 21 2.8 0.7 59 0.16 0.43 5th 21 4.7 1 .3 97 0.15 0 .64 6th 86 0 .1 6 Total 14 11 .0 2.6

All spiders used in this laboratory study were reared from egg sacs and wer e individually housed in plastic containers that measured 30 X 16 X 8 .5 cm. Wooden dowel rods cemented into each container provided web attachment sites . Spiders were kept at 23-25°C and 85-95% relative humidity and maintained on a 10:14 hour light :dark cycle. I checked these spiders daily and blew one wild typ e Drosophila melanogaster (both males and females were used) into each web the y produced . I recorded the duration of a complete prey wrapping sequence an d from this subtracted periods of inactivity and prey transport to obtain actual prey wrapping time, I began timing feeding when a prey's thick silk swathing becam e transparent as it absorbed digestive enzymes, checked specimens every 10-1 5 minutes thereafter, and noted when the spider had discarded its prey . These extracted prey were collected, placed in a vacuum desiccator wit h desiccant, and stored until the study was completed four and one-half month s later, at which time they were pooled by instar and weighed on a Metier ® H-3 1 AR balance. At 6-8 week intervals during this study, three samples of 100 fruit flies each were taken from the stock cultures used to feed the spiders, placed in a clean vial, heat-killed by holding the vial over a steam jet for 5 seconds, sprea d on filter paper, and placed in a vacuum desiccator . From the mean dry weight o f these flies (0 .19 mg, range 0 .17-0.23 rng), I subtracted the mean dry weight of th e prey discarded by spiders of each stadium to obtain prey extraction values . Table 1 summarizes the number of prey consumed during each stadium and th e amount of material extracted from each prey . The numbers of prey eaten b y males and females are combined because t-tests reveal no significant difference (p > 0.05) between them. Only the mean numbers of flies eaten by fourth and fift h instars differ significantly (p < 0.05) when compared with t-tests . The amount of material spiders extract from flies doubles after the third instar , but shows no increase thereafter (Table 1) . The small size of third instars may limit the volume of digestive enzymes they can produce and make available t o them only half the potential food of a fruit fly . Although the number of prey consumed by third and fourth instars does not differ significantly, this increase d extraction by fourth instars is responsible for their having a 34% greater tota l prey extraction (mean number of prey consumes X mean extraction) than thir d instars. The greater number of flies eaten during the fifth stadium results in a further 49% increase in food intake . Table 2 documents a 77% decrease in wrapping time and an 84% decrease i n feeding time from third to sixth stadia. The percentage of prey handling time devoted to wrapping drops by half after the third stadium, but remains constan t thereafter. Extraction efficiency increases during development, with fourth instars

1988 . The Journal of Arachnology 16:274

Table 2 .-Developmental changes in Hyptiotes cavatus prey handling . All times are in hours . Extraction values are in mg dry weight .

mg WRAPPING TIME FEEDING TIME TOTAL TIME PER FLY EXTRACTE D % PER HOUR INSTAR No . Mean SD No . Mean SD No . Mean SD Wrapping FEEDING 3rd 31 0.44 0.22 21 6.55 4.31 11 6 .25 4 .54 7 0 .01 2 4th 35 0.34 0.12 10 10.31 4.18 10 10 .67 4 .25 3 0 .01 6 5th 42 0.22 0.06 20 5.21 1 .42 20 5 .41 1 .42 4 0 .02 9 6th 20 0.13 0.05 12 3.06 0.70 12 3 .18 0 .73 4 0 .052

acquiring 1 .3 times more food per hour of feeding than third instars and fifth and sixth instars each removing 1 .8 times more food per hour than subsequent instars (Table 2). The laborious prey wrapping characteristic of uloborids (see Lubin 1986 for a review) may compensate for their lack of poison glands and their inability t o inject prey . Lubin (1986) found that prey type and mass influence the thoroughness of uloborid wrapping. All spiders of this study were fed the same type of prey and, judging by the opacity and smoothness of the wrapped flies , wrapping thoroughness remains relatively unchanged during development . Therefore, the shorter wrapping times characteristic of later instars probabl y reflect increases in the aciniform silk glands and spigots used in prey wrappin g (Foelix 1982) and reductions in the time required for spiders to circumscribe a prey during early wrapping stages and to manipulate a partially swathed fly during latter wrapping stages . Together with the previous developmental study of H. cavatus (Opell 1982) , these results emphasize the small cost of web production . Accidental web damage caused spiders to receive an average of only 0 .84 flies per web constructed . Despite this, their development times did not differ markedly from those of natural populations. Although wrapping and feeding times differ among instars, the proportion o f each stadium's "web construction" phase (Opell 1982) devoted to prey handlin g remains surprisingly small and constant. Third instars devote 4 .8% of this time to prey handling, fourth instars 7 .3%, and fifth instars 5 .5%. Matthew H . Greenstone and Yael D. Lubin made useful comments on this manuscript .

LITERATURE CITED

Foelix, R . F. 1982 . Biology of Spiders . Harvard Univ . Press, Cambridge, Massachusetts, 306 pp . Lubin, Y . D. 1986. Web function and prey capture behavior in Uloboridae . Pp. 132-171, In Spider - Webs, Behavior, and Evolution. (W. A . Shear, ed .). Stanford Univ . Press, Stanford . Opell, B. D. 1982 . Post-hatching development and web production of Hyptiotes cavatus (Hentz) (Araneae). J. Arachnol ., 12 :105-114.

Brent D . Opell, Department of Biology, Virginia Polytechnic Institute an d State University, Blacksburg, Virginia 24061 USA .

Manuscript received December 1987, revised March 1988 .