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POPULATION ECOUXTY Host Utilization by the Walnut Fly, Rhagoletis jugJandis (Diptera: Tephritidae) C^SAR R. NUFIO/ DANIEL R. PAPAJ,*- ^ AND HENAR ALONSO-PIMENTEL"- ^ Envifon. Ehtomal 93(S); 9M-1001 (2000) ABSTRACT BhagaletU jugfandit Cresion is a specialist that deposits its eggs into the husks of developing walnut fruit. Like other walnut infesting Bies in the R juocit group, A jugtandi* actively superpaiasitizes its larval hosts. However, little is known regarding the degm to which hosts are reused and the ecological contest under which host reuse occurs. This field study examined the pattern of host utilization by KJuglandit and how frait variables such as volume and penetrability affect the degree that hosts are reused. Fruit on four of five study trees were synchronously infested and within 2-2.5 wk ail fruit on these trees were infested. Fruit on a fifth tree were significantly less penetrable than those found among the other trees in the study and this may esplain why fruit on this tree were larely used thraughout the season. Walnut hosts were commonly multiply infested and reuse of hosts uccuiied in as few as 1-2 d after first infestion. Infestation levels within fruit appeared to itahili7C 4-5 d after fruit were first used. Fruit volume was positively correlated with both the number of punctures on hosts and the infestation leveb within hosts that had been infested for either 1-2 or 4-9 d. Large fruit were infested more quickly than small fruit, although this trend was stronger on some trees than others. Finally, despite a size-penetiability correlation among two of the five trees, penetrability itself did not explain either which fruit were preferentially used throughout the season or the infestation levels within fruit. KEY WORDS RhagpUti$juglandis, walnut flies, superparasitisin. marking pheromone, Tephritidae CHOOSINC WHEBE OFFsnuNc will develop is a simple form of maternal investment among insects. Oviposita'onai choices are especially important for insects whose larval stages are restricted to a particular environment or host. In such insects, offspring are themselves limited in their ability to acquire new resources iftheir natal resources become depleted (Messinaand Renwick 1985, Smith and LesseUs 1965). Maternal investment may involve avoiding laying eggi at sites previously used by conspecifics, a tendency often mediated by use of a marking pheromone (ftokopy 1981a, Roitberg and Prokopy 1987). Frugivorous fhiit flies in the fiunily Tephritidae deposit egg clutches within the husks of devek>ping fhnt where their larvae are constrained to feed and devek>p. Females may possess visual and chemical mechanisms for assessing the quality of available hosts and for discriminating between previously infested and uninfested hosts (Prokopy et aL 1976, Prokopy and Roitberg 1984, Henneman and Papal 19n). Females in the genus Rhagpletis assess and reject infested fiuit on the basis of a marking pheromone that is deposited on the &uit surface after oviposition by previous females. Thus, marking pheromone in this s]êm is believed to minimize larval competition by causing females to ' falenllsupUiwy Piugiiiu in bnect Scieiices, Univenity of Arizona. Tucson. AZ SS721. 'Department of Ecology and Evohilioaaiy Biolaor, Univcisily of Afizooa. Tucson, AZ SS72L 'Center (or buect Science. Univeisty of Arizona, Tucson. AZ aS721. «M6-2ZSX/00/09»4-l(nitQ2J»/0 O 2000 BUomologicJ Society of America distribute their clutches more uniformly within host patches than is expected by chance alone (Prokopy 1981a, 1981b; Bauer 1986; Averill and Prokopy 1989). Rhagoletis jugfandis (Cresson) is a member of the walnut-infesting fUutgofetis stidois group (Bush 1966). In southern Arizona this species is found on the Arizona walnut, Juglans nutfor (Torr.). which can be fotmd in montane canyons (1,200-2.700 m). These flies are univohine and females deposit clutches of up to 30 eggi after puncturing the firuit surface with their ovipositor. The larval stages feed on the husk of developing fruit, ptipate in the soil beneath the natal tree, diapause as pupae through the winter and spring, and emerge as adults during mid- to late summer. After deposition of a clutch, female R. juglandis drag their ovipositors on the firuit siu&ce in a manner suggesting deposition of a marking pheromone. Despite displaying the genus-typical marking behavior, female wût flies reinfest and often retise the actual oviposition sites established by conspecifics (Papaj 1994). Althotigh superparasitism, the use of hosts that already bear conspecific brood, is commonly associated with the lack of available hosts (Roidierg and Mangel 1988, Papq et aL 1989), walnut flies prefer infested hosts early in the season when uninfested hosts are still available (Ladonde and Mangel 1994). To explain superparasitism by walnut flies, researchers have proposed that the reuse of the oviposition sites provides females with direct benefits such as reduced ovipositor wear (Papaj 1993), reduced time to deposit clutches (Pap^ and Alonso-Pimentel 47
996 ENVIRONMENTAL I 1 s w 0.S • "8 0.4 § \ «•* I IS 17 It 21 23 28 27 2t 31 Jaly Fig. I. Proportion of study fruit punctured over die season (n = 232). By 31 July, all &uit on each of the study trees werr punctured. festation levels found in fhiit that had been infested for either 1-2, 4-5 or 8-9 d. Results Although five trees were in the original design, one tree (labeled A4 and located in lower Garden Canyon) was eventually eliminated because we observed few R Juglatdis individuals in mid-July and almost no flies in this tree during any other census date. By the end of the season, only 12 fhut. which included tagged and untagged fruit, were found to be punctured. Even at the end of the season the fniit on this tree were smaller (F= 46.6; dr= 4.180; P< 0.0001; Tukey HSD, P < 0.05 for each of four comparisons) and less penetrable (F = 38.2; df = 4,70; P < O.OOOl; Tukey HSD. P 0.05 for each of four within tree comparisons). A weak but significant negative correlation between fhiit volume and fhiit penetrability was found for both the unpunctured haphazard samples and fhiit punctured on the fint two census dates within trees A1 and A2 (regression coeCBcient = -0.0173, t = —481, df = 52, r' = 0.31, P = 0.0004; regression coefficient = -0.01, t = -2.5, df = 55, r* = 0.10, P = 0.015; trees A1 and A2, respectively). There were no significant differences between the slopes of the fhiit volumes versus penetrability data within these trees for the unpunctured sample versus the recently punctured fhiit (F = 2.00; df = 1,50; P = 0.79; F= 2.85; df= 1.53;P = 0.10, trees A1 and A2, respectively). There was also no significant differences in the slopes of the (hiit volumes venus penetrabih'ty data between trees A1 and A2 for the unpunctured sample and the recendy punctured (hiit (F = 0.96;df = 1,92; P = 0.33).To simplify the graphic representation between penetrability and fhiit volume within trees A1 and A2, we pooled the unpunctured haphazard sample and recently punctur^ fruit data from both trees (regression coefficient = -0.02; »= -S82,df=94.r* = 0.26,P 0.05). Infestition Level and Fruit Volume. On-estimate of the average (±SE) dutch size deposited by females during a singje oviposition event was 15.7 ± 1.5. The average infestation level of hosts increased with age of fruit The number of eggs deposited in a single ovqiosttion event was sîificantiy less than the infestation levels found in fruit collected 1-2,4-5. or 8-9 d afW they were fint infested (F = 33; df= 3,24; P
Page 1: INFORMATION TO USERS This manuscrip
Page 4 and 5: UMI Number: 3053915 Copyright 2002
Page 6 and 7: STATEMENT BY AUTHOR This dissertati
Page 8 and 9: DEDICATION This work is dedicated t
Page 10 and 11: ABSTRACT Choosing where offspring w
Page 12 and 13: An explanation of tiie problem CHAP
Page 14 and 15: euse occurs in the field, the impac
Page 16 and 17: Appendix D, "Aggregative behavior i
Page 18 and 19: offspring performance. Counter to t
Page 20 and 21: Lalonde RG, Mangel M, 1994. Seasona
Page 22 and 23: APPENDIX A HOST MARKING BEHAVIOR IN
Page 24 and 25: kluwer the language of science Dr.
Page 26 and 27: 174 belter categorized as cues than
Page 28 and 29: fubfe 2. Kinds ot cvicknce used lo
Page 30 and 31: 278 defend themselves and because i
Page 32 and 33: 280 lion of a signal. Costs associa
Page 34 and 35: 282 than were conspccifics with low
Page 36 and 37: 284 thai (he marker was a mutant fo
Page 38 and 39: 286 dropping on ihe MP communicatio
Page 40 and 41: 28S inac>. 3 larval partsiloiil of
Page 42 and 43: 290 Hol'svang. T. 1988. Mechanisms
Page 44 and 45: 29Z Roitbcfg. B- D it R- G- Laionde
Page 46 and 47: APPENDIX B HOST UTILIZATION BY THE
Page 48 and 49: Dispersal by Larvae of the Stem Bor
Page 52 and 53: October 2000 NUFIO ET AL.; HOST UTI
Page 54 and 55: October 2000 Nufio et au: Hoct Unuz
Page 56 and 57: October 2000 NUFIO ET AL4 HOST UIHI
Page 58 and 59: Reuse of larval hosts by the walnut
Page 60 and 61: KEYWORDS Life history" marking pher
Page 62 and 63: Alternatively, a weak correlation b
Page 64 and 65: previously attacked hosts early in
Page 66 and 67: walnut fly oviposition punctures. T
Page 68 and 69: Effects of offspring weight on adul
Page 70 and 71: she deposited over a lifetime and t
Page 72 and 73: RESULTS Levels of host reuse in the
Page 74 and 75: Survival from egg to egg hatch Of t
Page 76 and 77: significantly correlated with pupal
Page 78 and 79: DISCUSSION While the femaie-prefere
Page 80 and 81: discriminate between hosts that hav
Page 82 and 83: will consume fewer resources and th
Page 84 and 85: females gain not by simply reusing
Page 86 and 87: of her offspring but also of the nu
Page 88 and 89: ACKNOWLEDGEMENTS We thank Henar Alo
Page 90 and 91: Bjorkman C, Larsson S, Bommarco R,
Page 92 and 93: Fujiyama N, Katakura H, 2001. Varia
Page 94 and 95: Mayhew PJ, 1997. Adaptive patterns
Page 96 and 97: Robertson IC, Roitberg BD, 1998. Du
Page 98 and 99: Wiklund C, 1981. Generalist vs. spe
Page 100 and 101:
Table 2. The influence of various f
Page 102 and 103:
Table 4. Analysis of variance compa
Page 104 and 105:
nCURE CAPTIONS - Continued Figure 5
Page 106 and 107:
Figure 1. Fruit Cohorts (Number of
Page 108 and 109:
Figure 3. A. B. A > on •m e « 50
Page 110 and 111:
Figure 5. B. es & 1 1 0.8 • 0.6 -
Page 112 and 113:
Figure 7. B. > 09 "S s e s o •Ml
Page 114 and 115:
Figure 9. 400 9t W s 1 t 300 « Of)
Page 116 and 117:
Aggregative behavior is not explain
Page 118 and 119:
that the larval aggregations that f
Page 120 and 121:
2001). The shifting benefits and co
Page 122 and 123:
spatial patterning of clutches depo
Page 124 and 125:
16-fl oz (473-ml) plastic Solo cups
Page 126 and 127:
percentage of hatchlings that emerg
Page 128 and 129:
previously created oviposition punc
Page 130 and 131:
RESULTS Experiment 1. Effect of off
Page 132 and 133:
deposited) again improved the model
Page 134 and 135:
median pupal weight in the lone two
Page 136 and 137:
survival, using two-clutch and thre
Page 138 and 139:
DISCUSSION Absence of an AUee efTec
Page 140 and 141:
simultaneously. It would seem that
Page 142 and 143:
Spatial distribution of clutches In
Page 144 and 145:
If reuse of larval hosts negatively
Page 146 and 147:
ACKNOWLEDGEMENTS We thank Henar Alo
Page 148 and 149:
Hausmann SM, Miller JR, 1989. Ovipo
Page 150 and 151:
Papaj DR, Alonso-Pimentel H, 1997.
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
FIGURE CAPTIONS continued Figure 4.
Page 158 and 159:
Figure 2 MD E DC n Om 3 Qi S V DA E
Page 160 and 161:
Figure 4. B. c. -g 60 S a. a 40 - S
Page 162 and 163:
Host marking beiiavior as a quantit
Page 164 and 165:
encountered either control fruit th
Page 166 and 167:
unparasitized and parasitized hosts
Page 168 and 169:
Finally, it is conceivable that the
Page 170 and 171:
Experiment 1. Relationship between
Page 172 and 173:
or 30 minutes). Fruit were then hun
Page 174 and 175:
After two replicates of the four tr
Page 176 and 177:
Experiment 3. Female responses to h
Page 178 and 179:
RESULTS Experiment 1. Effects of cl
Page 180 and 181:
Experiment 3. Female responses to f
Page 182 and 183:
example, the possibility that ovipo
Page 184 and 185:
field cage assays. What remains to
Page 186 and 187:
ACKNOWLEDGEMENTS We thank Henar Alo
Page 188 and 189:
Bauer G, 1986. Life-history strateg
Page 190 and 191:
Landolt PJ, Averill AL, 1999. Fruit
Page 192 and 193:
Quiring DT, McNeil JN, 1984. Intras
Page 194 and 195:
FIGURE CAPTIONS Figure 1. The relat
Page 196 and 197:
Figure 2. w OA 8 k 98 s o a. QH s 8
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