Different brood densities were produced under a constant bark surface area of the spruce host, by excising egg-producing female &lt;i&gt;Dendroctonus rufipennis&lt;/i&gt; from the host material after they had excavated galleries of specified lengths. This procedure allowed a constant attack density. The numbers of adult progeny produced/cm of egg-gallery were significantly greater from bark slabs with short galleries and low densities: the sizes (pronotal widths) of adult progeny of both sexes were also significantly greater from low than from high densities; and the distribution patterns of chromatin differed significantly among high, medium and low densities

Ibaraki, A.

Peet, F. G.

Sahota, T. S.

English

Journal of the Entomological Society of British Columbia

J. ENTOMOL Soc. BRIT. COLUMBIA 84 ( 1987), D EC. 3 1, 1987 59 MANIPULATIONS OF EGG-GALLERY LENGTH TO VARY BROOD DENSITY IN SPRUCE BEETLE DENDROCTONUS RUFlPENNIS (COLEOPTERA: SCOLYTIDAE): EFFECTS ON BROOD SURVIVAL AND QUALITY T. S. S A HOTA, F. G. P EET AND A. IBAI{AK I Canadian Forestry Serv ice , Pacific Forestry Centre, Victoria , British Co lumbia. V8Z I M5 Abstract Different brood densities were produced under a constant bark surface area of the spruce host , by excising egg-producing female DendroclOnlls 1'lIjipennis from the host material after they had excavated ga lleries of specified lengths. Thi s procedure allowed a constant attack densily. The numbers of adult progeny produced/cm of egg-ga llery were sign ificantl y greater from bark slabs with short ga lleries and low densities: the sizes (pronotal widths) of adult progeny of both sexes were also significantly greater from low than from high densi ties; and the distribution patterns of chromatin differed signi fi cantly among high, med ium and low densi ties. Resume Les auteurs ont obtcnu differentes dcnsites d'oeufs sous une section con stante d ' ccorce de I 'epinette hote en retirant des femelles ovipares de DendroL'IOI1I1S mjipenllis du tisslI hote apn':s qu 'e lles aient creuse des galeries de longueur determinee. Cette methode permet d 'obtenir une den site d 'i nvas ion con stante. Le nombre de descendants adu ltes produit par centimetrc de galerie de ponte etai t beaucoup plus c levae dans les sec tions d 'ecorce a galeries courtes et a densi tc d 'oeufs faibl e; la tai lle (Iargeur du pronotum) des descendants aduJtes des deux sexes etaient ega lement beaucoup plus e levee lorsque la densite des oellfs etait faible. De plus, les modes de repartition de la chromatine differaient enorlllcmcnt se lon qu 'c lle provenait d 'oeufs it fort e. Illoyenne ou faibl e dens ite. Introduction In population dynamics studies of ba rk beetles. the effec t of density o n brood production has been s tudied mostly in relation to the attack dens ity of the parent bee tles (McMullen and Atk ins 1961: Cole 1962; Reid 1963; Berryman and pienaar 1973). Studying this re lati onship carries practica l advantages in that the a ttack density can be readily detemli ned in na tural stands w itho ut destroying the sampl e and variat ions in a ttack dens it y <.:an be eas il y created in cOl1lro ll ed experiments. Such experi ment s, however, do not di scrim inate betwee n red uced brood production due to fewe r parc nt beet les ( McMull en and A tkins 1961: Thomson and Sahota 1981) and that due to brood dens ity and competition among the progeny. Some ex pe riments . us ing thi s approach , have re lated brood qu a lity, such as adult s ize in the brood , to the dens it y o f pa rental attac k (Re id 1962: McG he hey 1971; Safrany ik and L inton 1985). Poss ibl y, the effect of a tt ac k density on brood is indirec t, emanating thro ugh changes in brood den s ity. Co le (1973) isolated the effects of brood density on the qUil lity o f the brood as ~hown by thei r reproducti ve capaci ty w hen m ature . Varying the density o f D elldroclOl1Us pOllderosae larvae on a phloem diet showed that increased dens ity and compe tit ion among larvae led to red uced reproducti ve ca pacity in the resu lting aduit females. In the present paper, we have iso lated the effects of brood densi ty from those of pa rental attack den s ity among progeny rai sed on the natural host diet. Su rviv a l and indi vidu al size of the brood adults are reported . A lso reported are cytological differences among the brood fro m the var io ll s dens ity classes as indicators of diffe rences in population qua lity. Materials and Methods T he spruce beetles . D elldruc(OIlIlS mfip l' l1l1is (Ki rby) used in th is study were co ll ected fro m a natura l endem ic field popul ation near Hi xon, B riti sh Columbia as we ll as the laboratory-reared progeny of these beetles. The bolts of host trees contain ing adult beetles were co llected from the fie ld and stored in the laboratory at O°C (± 1°C) from Octob r to April. 60 1. ENTOMOL Soc. BRIT. COI.UMBIA 84 ( 1987), DEC. .3 1. 1987 In May the bolts were transferred to cages at room temperature leading to emergence of the beetl es. Fresh host material was obtained from the beetle collection s ite by c utting a spruce tree (Picea engelmannii Parry ) of 34-cm-dbh. Bark-bearing slabs measurin g 30 cm x 20 cm x 5 em thick were cut out of the bolc. Surfaces without bark were eoated with molten paraffin wax to avoid excess ive moisture loss. Eac h female beetle was introdueed 5 cm from one end of each slab by making a small hole in the bark and confined there with a ge latin capsule. The male followed the femal e one day later. Infested s labs were maintained at 18.3 ± 1°C, eac h standin g on its beetle-containing end to encourage directiona l gallery prod ucti on by the bee tl es. This arrangement was used to produce three sets of slabs (9- 10 slabs/set) containing parental ga lleries of 6.8 cm, 9 .8 cm and 12.8 cm while the bark surface areas of all the s labs rema ined identical. The required gall ery length was achieved by X-raying the slabs and exc is ing the fema le at the proper point. Beetle exc ision was carried o ut by cutting about I cm x I cm piece of the bark . Thi s opening was sealed wi th mo lten paraffin after removal of the femal e. It was no t possible, however, to exc ise each beetl e at precisely the spec ifi ed gal lery length . Eighteen slabs were started for each den sity leve l: 9-10 of these we re success full y co loniz.ed for each leve l. The three brood densities resulting from these ga ll eries were des ignated as low. medi um and hi gh respectively. The slabs con tai ning the parental galleries and eggs were kept at 18.3°e. In Se pte mber, when the progeny had reached the adult stage, the s labs were placed at O°C for over-w intering. The slabs were peeled to rem ove the adu lt progeny in May of the followin g year. The total parental ga ll ery length, the egg-gall ery length (tota l parental gal lery - ini tial egg free ga ll ery) and the numbe r of adults prod uced in each s lab were recorded. The pronotal widths o f all proge ny were measured and the ir sexes determi ned. Cytolog ica l investigat ions rel ati ng to quality d ifferences among progeny from differe nt densities were carried ou t by ana lys ing di g it ized images of fa t body nu c le i (Sahota el al . 1984). Ten to 15 females from each den sit y grou p were fixed in 3 parts et hanol: I part ace ti c ac id for 2h. The ir abdomens were s lit open to faci litate penetration o f fi xa ti ve. The fa t body was stained in s itu with Fue lgen sta in a fter a 20 min hydro lysis w ith 3.5N HC I at 37°e. T he fat body ce ll s were spread on mic roscopic s l ides as descr ibed by Farris ('( al. (1982). Digitized images of fa t body nucl e i we re created by scanning the samples at 570 nm using a Ze iss SMP5 micropho lOmeter system on line to a PDP 11 /34 minicomputer. Thi s process meas ures the li ght tran sillill ed thro ugh every 0.25 !Jill square of the scanned area produc ing a matrix of numbers or the di g itized image. Materia ls othe r than nuclei in the di gitized images were reilloved by editi ng. Seventy-rive variab les were mathemat ically derived from each of the edi ted images. Derivation o f these varia bles or features a lo ng with the scanning and edi ting proced ures are described in Peet and Sahota (1984. 1985) and SahOla (' / al. ( 1986) . For analysis of data dea li ng with ga llery le ngth s. progeny produced. and average individual size of the proge ny at various densi ties, we used ANOYA fo llo wed by Newman-Keul 's multiple range tes t. The re lat ionship between the adult progeny per unit of egg-ga ll ery length at var io us densities was examined by regression anal ysi s. To in ves ti gate cytologica l diffe rences among progeny groups from dil'ferent densit ies, the three features wit h the hi ghest meri t value for discriminating among the three dens ity classes we re se lec ted by the compu ter. These included a hi stogram feature (HI ST04) and two transit ion probabilit y features (TRPR23 and TRPR6 1). Histogram featu res examine the probab ilit y of the pixels of a nucleus be longing to a g iven optical densi ty bin o f a 20-bin hi stogram generated from the optical dens ities o f all the pixels compri s ing the nucleus. HI ST04 refers to the fo urth bin of such a hi stogram. Transi ti on probabilit ies relate to the degree o f change of opt ical densit y between a pixel and its eight immed iate neighbours. A detail ed description of these and other fea tures is given in Peet and Sahota ( 1984). We appli ed di scrimi nant analysi s (Cooley and Lohnes 1971 ; Duda and Hart 1973) to the above three fe atures of the three cell populations. These methods generated a set of axes that maximized the distances between the d istributi ons re presenting various popu lations and minimi zed the d istances withi n each di stribution. The 99% confidence ellipses were drawn with respect to the first two of these new variables as th e two axes. A more detai led desc ription of this application J. ENTO MOL Soc. BRIT. COLUMBIA 84 ( 1987). DEC. 3 1. 1987 61 of discriminant analysis is given in Sahota et al. (1 986). Results and Discussion Changes in brood density per 20 cm x 30 cm bark surface created by the variations in the length of egg-gallery resulted in changes in the pronotal widths of brood members as well as their survival to the adu lt stage. There was a significant 'decrease (p < 0.0 I) in the pronotal widths with increas ing brood density in both sexes (Table I). This is similar to the results obtained by varying the attack density (Safranyik and Linton 1985). The three groups of egg-gallery lengths created for producing the three brood density classes were significantly different from each other (P < 0.05). However, the number of adult progeny per slab or per cm of the egg-gallery differed significant ly between high and low densit ies but neither differed from the medium density (P > 0.05) (Table I ). When adult progeny per un it length of the egg-gallery was plotted against the length of such galleries (Fig. I), it was shown that increased egg-gall ery length and competition led to a decrease of adult progeny produced per cm of this gallery. The relationship depicted in this fi gure was significant at the 95% confidence leve l. Thus it appears that the range of brood densities created in the ex periment produced biological effects of competition on brood su rvi val. Safranyik and Linton (1985) concluded that fewer adults produced per unit length of the egg-ga llery with increas ing density was due to brood mortal ity. In their experiments, however, differences in brood density were created by varying the attack density of parent beetles per unit area of bark surface. Their argument that the decrease in adult progeny per unit gallery length was not due to a decrease in egg production, was based on the demonstration by Thomson and Sahota ( 198 1) that competition among parent beetles does not a lter the number of eggs deposited per unit egg-ga llery length. The present res ults are in agreement with those of Sefranyi k and Linton ( 1985) but provide more direct evidence to show that the decrease in adult progeny produced per unit length of the egg-gallery was so le ly due to brood competition as parental attack density was constant in these ex periments. It may be pointed out that in most of the slabs less than 70% of the phloem was used by the brood. In two of the slabs nearly 90% of the ph loem had been used. 12 I >- 10 " Z W ...J >-a: 8 w ...J ...J '" .". " • LL 6 0 ~ E . u . "- 4 ..,; "-0 a: a.. ':i 2 :;) 0 '" 4 6 8 10 12 GALLERY LENGT H (em) Fig. I. Influe nce of egg-ga ll ery lengIh (brood densi ty) on the survival per em vf egg gallery vI' [klldroc/OIIIIS rutfpell' lis brood in 30 elll x 20 em of hal"k surface area. 62 J. EN 'I I)MOL S()c. BR IT. C O U IMIl IA g4 ( 1 9~7 ), D EC. 3 1, 19R7 Table I. Egg'ga llery lenglhs of the pare nt udult s and some characteristics o f their "du ll progeny raised at three brood dens ity leve ls on 30cm x 20cm , lab, of Picea el/~"'n/(/I/I/i. Broo d De n sit:r: Level High tle diurll Low No. of parental 9 9 10 egg-galleries Egg - gallery 8 . 81 a 6 .01 b 3 .72 Lengths (em) (0.40) (0 .02) (0 . 41) Adult p rogeny 42.8 ab 38 . 7 be 23 . 8 e per b a rk slab (4 . 9) ( 5. 0) (2.4) Brood adult s produced 4. 8 1 ab 6 .1 5 b e 7.09 per em . of egg- gallery (0 .42 ) ( 0. 88) ( 0 . 91) Pronota1 widths o f Fe male 2 . 14 a 2.2 9 b 2.38 brood adult s (mm) (0.00 4 ) ( 0.005) (0 . 01) Hale 2.0') a 2 .29 b 2 . 34 ( 0 .003) (0.007) (0 . 0 1 ) Note: Nu mbers", it hin brac ~ e t s show the stallliarcl error orthe means they are ussocialecl with . Means followed by the same letters within each ro w arc not signii"iccntl y di ffe rent at l)S'k lcwl (Ncwman- Kcul '; mul ti ple range test) . Effec b of the brood density on the " popul at ion quali ty" o f the progeny were investi gated by exam ini ng ind iv idual sif.e (pronola l width) in the progeny and changes c reated in the distri but ion pal1ern ~ or chromatin (DNA ). lnerease in brood density created by the inc rease in len gth o r the egg-galkl ies resu lted in a s ignificant reduc ti on PI' the ind ividual s i/e of the proge ny or bo th se xes (Tabk I ). Broud dCll si ty a lso pr0d uccd cytological changcs in the fa t body nuclei wh ich reveal signi ficant differences alllong the progeny ['rol11 the three b rood de nsity classes. Fig . 2 show~ the 99'X confi dence ellipses of the mcans of the progeny from the three den s it y c las~e:-.. The~e el l ip~es are ha<,ed 011 the three feat ures with the hi ghest merit value deri ved from the distr ibuti on patt e rn of chromati n. Chromatin di :-. tribu tion pa ttern have been used to demonstrate small differences amon g ce ll alll! insec t pop ul ations ( Barte l ~ and W ied <J77; Bartels and O lson 1980; Sahota (' I ai, 1984) . Furthe rm ore , Sahota CI al. ( 1986) have sho wn tha t changes in the functions of the diffe ren ti ating fo llicu la r e pithe lia! ce ll s are accompanied by changes in the chromat in d istr ibution patt e rns and that the treat ment s lead ing to bloc kage o f func ti onal d iffe rentiation of these ce ll s a lso bloek changes in chromati n di stribution patterns , thu s providin g evidence for a re lati onsh ip be tween c liromat in distribu-tion patte rn and cel l fun ction . The result s presented in th is pape r ~ho", that the i nfluence ~ o f brood dens ity on the surviv a l and quality o f the progeny are :-. itl1ilar to those created in response to a ttack densi ty (See Safrany ik and Linton 1985) . It appea rs that attac k densi ty effec ts are produced indirectly through brood den :-. ity as a resu lt of compet ition. T he resu lts a lso show that ana ly,i s or chromatin distri bution pattern~ can detect populat ion q ualit y d iffe rences c reated by brood de ns ity and com petition. Sahota CI (/1. ( 1984) ha ve po inted out tha t popul at ion qual ity d ifferences re lated to re productive ca pac ily may res ult from the influence of a vari e ty o f fac to rs such as en vironment, gene ti cs, competi ti on, disease , etc. However, chromatin di st ribu-tion pattems resulting fro m the in flu ence of these fac tors may be d iffe ren t. Thus, dens ity-re latec! distributi on pattems of c hrom atin in broods provide further information required to build a comprehensive pictu re o f c hrom atin di str ibu tion patterns in re lation to pop ul at ion q ua lit y and reproduc tion . e e e e J. ENTOMOL Soc. BRIT. COL.UMB I A 84 (1987), DEC. 3 1. 1987 63 DISCR IMINANT VARIABLE I 2 4 6 8 N W ...J <D :'! MEDIUM LDW a: " 4 HIGH > >-z " z ::;; a: 6 u '!' 0 8 Fig. 2. Ninety-nine percent confidence ellipses of the means of distribu tion of the DendrocfOlllIs rlijipellllis broods raised under three different densit ies . These distributions arc based on patterns of chromatin dis tribution. References Bartels. P.H . and G.L. Wied. 1977. Computer analysis and biomedical inte rpretation of microscopic images: current problems and future directions. Proc. IEEE. 65: 252-262. Bartels , P.H . and G.B. Ol son. 1980. Computer ana lysis of lymphocyte images . ill Methods in Cell Separation. N. Catsimpoolas (ED.) 3: pp. 1-67 . Plenum Press. New York. Berryman. A.A . and L.v. Pienaar. 1973. Simulation of intraspec ific compet ition and survi val ofScolrllls I'etllralis broods (Co leoptera : Sco lyt idae). EIII 'i roll . t : f1I . 2: 447-459. C ·Ie. W.E. 1962. 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Manipulations of egg-gallery length to vary brood density in spruce beetle, Dendroctonus rufipennis (Coleoptera: Scolytidae): Effects on brood survival and quality

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Manipulations of egg-gallery length to vary brood density in spruce beetle, Dendroctonus rufipennis (Coleoptera: Scolytidae): Effects on brood survival and quality

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