Cross-attraction of Five of Stored-product (: ) in a Wind Tunnel

P L PHELAN AND T C BAKER Department of , University of California, Riverside, California 92521

Environ Entomol 15: 369-372 (1986) ABSTRACT Sharing of the sex-pheromone communication channel by five species of P~Y- citine was measured in a wind tunnel Overall, male pheromonal response was char- acterized both by high levels of interspecific attraction and broad overlap in the circadian periods of male response, with attraction to nonconspecific females 75%of that to conspe- cifics, on average cautella (Walker),Plodia interpunctella (HCbner), and Anagasta kuehniella (Zeller) males demonstrated high levels of upwind-flight response throughout an 8-h scotophase P interpunctella and A kuehniella males responded to nonconspecific fe- males at levels that were as high as to conspecifics elutella (HCbner) males showed the greatest level of response discrimination with the probability of flight to nonconspecific females only 41%of that to conspecific females, although relative importance of pheromonal differences and temporal effects could not be determined Poor reproductive isolation by long-distance parameters points to a greater reliance on less efficient short-range mecha- nisms, such as courtship and male pheromones Significance of these findings to current thought concerning evolution of reproductive isolating mechanisms is considered

DESPITETHE APPARENT limited number of com- Analysis of male response to conspecific and non- pounds that are utilized in the sex pheromone conspecific females was carried out in a wind tun- blends of most Lepidoptera and the sharing of nel to partition the variables that can obscure this many of these compounds, especially among closely measure related species, the chemical communication sys- tems of most moths remain highly species-specific Materials and Methods and act as important reproductive isolating mech- anisms in many groups (Roelofs and Blown 1982) Five phycitine species were utilized in this study: There are, however, exceptions to this general pat- (Hubner), P interpunctella, tern, as interspecific attraction has been reported Anagasta kuehniella (Zeller), for Plodia interpunctella (Hubner) and Cadra (Gregson), and C cautella Colonies of each species cautella (Walker), both in laboratory studies (Gan- were maintained separately on artificial media af- yard and Brady 1971) and in the field (Ganyaid ter the procedures described by Strong et a1 (1968) and Brady 1972) This cross-attraction is at least Individuals were separated by sex at the pupal in part due to (Z,E)-9,12-tetradecadienyl acetate stage, and adults of all species were maintained on (Z,E-9,12-14:Ac), a compound that has been re- concurrent 16:8 (L:D) photoperiods with access to ported as a major component of the female pher- a 15% sucrose solution E elutella was obtained omone of a number of other phycitine moths (Vick from a laboratory colony at the University of Cal- et a1 [I9811 and references therein) These species, ifornia, Riverside; the remaining species were in members of the so-called stor ed-pr oduct complex culture < 1 year, having been established from wild of phycitine moths, are largely cosmopolitan and populations collected in the Riverside area are frequently found in an intense form of sym- Voucher specimens for each species were pre- patiy, coinhabiting grain warehouses and food pared and are available for examination stores (Levinson and Buchelos 1981) Temporal Females were tested for their ability to elicit " overlap in the periods of sexual activity of some upwind flight of males in a wind tunnel during species has also been reported, although Kr asnoff their respective periods of peak calling (Kr asnoff et a1 (1983) pointed to temporal differences of et a1 [1983] and references therein) For C cau- female calling behavior as a possible mechanism tella, this was 0 5 h after the initiation of scoto- ^ for reproductive isolation in othei species of this phase; for C figulilella, 4 h into the 8-h scoto- phase; and for A kuehniella, during the last hour The present study investigates the species-par- of scotophase P interpunctella and E elutella titioning of the sex-pheromone communication display broad windows of calling behavior, with channel of five species of Phycitinae and measures >50% of the females calling during the second to the degree of isolation that can be attributable to the eighth hour of a 10-h scotophase (Krasnoff et female pheromonal differences and temporal dif- a1 1983) These two species were tested beginning ferences in the sexual activity of these species either with the second or the sixth hour of scoto- 369 Vol 15, no 2 phase, the order of which was alternated between Table 1. Percentage of males of four phycitine species replicates Before the initiation of scotophase, flying 3 m uptunnel and landing on a cage containing one 2- to &day old females of each species were trans- of five species of females ferred (two per cage) to cylindrical screen cages f (4 cm diam by 4 cm long) Males were placed in attrac- the tunnel room 1 h before scotophase. SS (%yb tion of At the time described above for each species, a n non- r A con- cage containing two females was placed on a sheet- 22 C cau- E elu- inter- kueh- specif- metal platform elevated 15 cm above the tunnel teb tells punc- niellu ics/ floor, 50 cm from the upwind end of a flight tunnel tellu con- (3 4 m long) described by Kuenen and Baker specif- (1982) The wind velocity was maintained at 0 42 ics m/s, with a light level of 0 4 lx and a temperature C cautella 80a llc 74a 74a 0 66 of 22 Â 3% A different metal platform was used E elutella 20b 60a 69a 71a 089 C fieulilella 80a 24bc 80a 67a - for females of each species to avoid possible pher- P ~erpunctella 40b 44ab 77a 76a 0 69 omone contamination To ensure that at least one A kuehniella 75a 20bc 76a 76a 075 of the females was calling, four or five conspecific i response to noncon- males were released from downtunnel to test for specifics/conspecifics 0 67 0 41 0 97 0 95 response If no response was observed, the females a Means for six replicates of five males per species were replaced with another pair of the same b Values within a column followed by the same letter are not species This occurred infrequently and the re- significantly different (P > 0 05; Ryan's [1960] multiple test for sponse of these indicator males, whether positive proportions) or negative, was not included in the analysis Once a positive response was obtained, five males of each species were individually released downwind of to the multi-species sharing of at least one sex the females by placing them within the phero- pheromone component, Z,E-9,12-14:Ac This sin- mone plume and allowing them to take flight from gle compound has been used in traps to simulta- a small screen cone in which they were held Test- neously monitor populations of several species of ing of males of all species for the females of each stored-product Phycitinae in warehouses (Levin- species required ca 1 h and the species order of son and Buchelos 1981) Within the no-choice con- males was randomized for each female, using six ditions of this study, males of both P. interpunc- replicates in a randomized complete-block design tella and A kuehniella demonstrated a response Male responses were statistically compared using to all nonconspecific females that was almost iden- Ryan's (1960) multiple test for proportions tical to that to conspecific females The high level Measurement of interspecific pheromone re- of attraction of P interpunctella males to females sponse by C figulilella males was not possible, as of C cautella is consistent with the work of Gan- attempts to elicit even intraspecific upwind flight yard and Brady (1971), who found that when Plo- by these males were unsuccessful When presented dia males were released in a room containing either with conspecific females, C figulilella males re- P interpunctella or C cautella females, they were sponded with wingfanning and by taking flight, attracted in equal numbers to the two species It but rarely exhibited oriented uptunnel displace- should also be noted, however, that when females ment to the females This could not be attributed of both species were present, males were much to a lack of calling by the females because males more likely to locate conspecific females than C of other species responded well to the same fe- cautella females, suggesting the presence of sec- males Despite many attempts to alter environ- ondary pheromone components in either one or mental conditions such as temperature, light level, both species and humidity, a consistent response could not be Sower et a1 (1974) have identified (Z,E)-9,12- evoked Use of two additional strains of this species, tetradecadienyl alcohol (Z,E-9,12-14:OH)as a sec- including the offspring from a feral population, ondary component of the Plodia female sex pher- was equally unsuccessful omone This compound was also found to reduce the response of C cautella males when combined with either conspecific pheromone extracts or syn- Results and Discussion thetic Z,E-9,12-14:Ac This explains the signifi- Response of males to nonconspecific females was cantly reduced response of these males to Plodia remarkably high for most of the interspecific com- females (40 versus 80% to conspecific females) in binations tested (Table 1) For the males of four the present wind-tunnel studies Furthermore, E species, the level of response to nonconspecific fe- elutella, another species to which C cautella males males was, on average, 75% of that to conspecific responded poorly (20%),also utilizes the alcohol as females These males flew 3 m upwind, landed on a pheromonal component (Krasnoff et a1 1984); the cage containing the females, and walked rap- response of C cautella males to C figulilella and idly around the cage while wingfanning A high Anagasta females (80 and 75%, respectively), from level of inter specific response is undoubtedly due which Z,E-9,12-14:OH has not been identified, was April 1986 PHELANAND BAKER:CROSS-ATTRACTION OF STORED-PRODUCT PHYCITINAE 371

comparable with their response to conspecific fe- of unique and precise ratios of the shared com- ponents in conjunction with a comparably precise E elutella males appeared to exhibit the most male response, and 3) temporal differences in diel discriminating response Their probability of flying per iodicities of sexual activity Species-specific upwind to any of the nonconspecific females was chemical communication in the Tortricidae is of lower than the probability of flying to their own paramount importance to reproductive isolation females; on average, interspecific response was 41% and well exemplifies the utilization of all these of that to conspecific females Interestingly, their mechanisms (Roelofs and Brown 1982) For ex- greatest interspecific response was to Plodia fe- ample, nine tortricine species may be found within v* males Again, this is probably due to the sharing a single apple orchard, all of which share phero- of Z,E-912-14:OH as well as Z,E-9,12-14:Ac as mone components with at least one other species pheromone components in these species and eight of which overlap in their periods of sex- In addition to high levels of overlap- in phero-- ual activity Five species in this group have two mone-modulated response, it also appears that components in common, (2)- and (E)-11-tetra- tempor a1 over lap is greater than previously SUP- decenyl acetate Archips semiferana (Walker) and posed Krasnoff et a1 (1983) considered the possi- Choristoneura rosaceana (Harris) maintain isola- bility that some reproductive isolation might be tion through precise differential ratios of these two provided by tempor a1 differences in sexual activity components The pheromone systems of A argy- periods between C cautella, C figulilella, and A rospila (Walker) and A mortuanus Kearfott are kuehniella, based on previous studies of female distinguished from those of other species by the calling periodicities in these species Although the presence of two additional components, (2)-9-tet- durations of male response periods typically ap- radecenyl acetate and dodecyl acetate, and are dif- proximate the circadian periods of female calling ferentiated from each other by unique blend ratios in moths (Roelofs and Card6 1974, 103), the results of the four compounds The fifth species of this of the present study indicate that males of many complex, Argyrotaenza velutinana (Walker), is re- stored-product Phycitinae have much broader in- productively isolated by a combination of tempo- tervals of responsiveness than would be suggested r a1 differences and differences in blend ratio by the calling windows of their females Males of The results of this study suggest that, in contrast P interpunctella and A kuehnzella responded to the mating systems of the Tortricidae and most equally well throughout the 8-h scotophase and C other groups, the long-range sexual com- cautella males showed high levels of response at munication channel of the stored-product Phy- the beginning, middle, and end of the scotophase citinae is poorly partitioned The utilization of sec- The reduced response of C cautella males to E ondary components in the sex pheromone, such as elutella and P interpunctella females cannot be in P interpunctella and E elutella, reduces the attributed to temporal effects and is likely due to pi obability of cr oss-attraction between some species differences in pheromonal chemist1y The breadth pairs; however, this isolation is far from complete of the period of E. elutella male response could for any of the species in this group This poor not be ascertained by this study Males responded isolation along such long-distance parameters as equally well to conspecific females, whether tested diel periodicity, , and female sex phero- at 2 or 6 h into scotophase; however, response to mone points to a greater reliance on less efficient, conspecific females was not tested before or after short-range factors Grant et a1 (1975) found high this 5-h period and may have been lower at these levels of reproductive isolation between C cautel- times Therefore, although pheromonal differ- la and P interpunctella to be effected in the ences probably are the cause of poor response to courtship arena due to differences in courtship be- females of C cautella and A kuehnzella, temporal havior and courtship pheromones Likewise, in the effects cannot be ruled out in this case courtships of E elutella and C figulilella, females Chemical identifications of female sex phero- of both species display strong discrimination against mones for over a hundred species of moths have nonconspecific males, making interspecific mat- uncovered a relatively limited number of different ing~improbable (unpublished data) These rejec- compounds; these are primarily even-numbered tions by females appear to be due to species dif- 10- to 18-carbon straight-chain acetates, alcohols, fer ences in male pheromones and aldehydes, although exceptional compounds Evolutionary theory predicts a relatively low have also been elucidated (Card6 and Baker 1984) level of energyltime expenditure for reproductive Despite a seemingly limited "alphabet" of chem- isolating mechanisms that have arisen through nat- icals, transmission of the sex pheromonal message ural selection, whether such mechanisms were ini- is, typically, highly species-specific Even when tially selected in response to interspecific mating sympatric species share one or more pheromone mistakes (Dobzhansky 1940) 01 simply to increase components, inter specific cr oss-attr action is usu- the efficiency of specific-mate recognition (Pater- ally very low (Card6 et al 1977, Greenfield and son 1978, 1982) Isolation at the courtship stage Karandinos 1979) This specificity may be brought occurs late in the mating process of moths, requir- about through a number of mechanisms: 1) use of ing considerable time wastage, especially for the additional pheromone components, 2) utilization male This apparent inconsistency necessitates the consideration of other models for the evolution of Krasnoff, S. B., KOW. Vick, and J. A. Coffelt. 1984. isolating mechanisms The possible role of sexual (Z,E)-9,12-Tetradecadien-1-01:a component of the selection in the evolution of reproductive isolation sex pheromone of Ephestia elutella (Hubner) (Lep- has been given greater attention recently (Thorn- idoptera: Pyralidae) Environ Entomol 13: 765-767 hill and Alcock 1983, West-Eberhard 1983) A sex- Krasnoff, S. B., K. W. Vick, and R. W. Mankin. 1983. ual selection explanation is more consistent with Female calling behavior in Ephestia elutella and E figulilella (Lepidoptera: Pyralidae) Fla Entomol 66: if the evolution of the phycitine mating system, in 249-254 that sexual selection would not necessarily favor Kuenen, L. P. S., and T. C. Baker. 1982. Optomotor an isolating mechanism with greater energy effi- regulation of ground velocity in moths during flight ciency In fact, such a selection process may occur to sex pheromone at different heights Physiol Ento- /' in the absence of pressure from interspecific mat- mol 7: 193-202 ing mistakes, with the reproductive isolation role Levinson, H. Z., and C. T. Buchelos. 1981. Surveil- arising only as an incidental by-product The evo- lance of storage moth species (Pyralidae, Gelechi- lution of isolating mechanisms has remained an idae) in a flour mill by adhesive traps with notes on area of unresolved debate for the past 40 years In the pheromone-mediated flight behaviour of male moths Z Angew Entomol 92: 233-251 the Lepidoptera, we presently entertain only a Paterson, H. E. 1978. More evidence against specia- shallow understanding of the relationship between tion by reinforcement S Afr J Sci 74: 369-371 reproductive isolation and the evolution of chem- 1982. Perspective on speciation by reinforcement S ical communication The role of sexual selection Afr J Sci 78: 53-57 in chemically mediated reproductive isolation in Roelofs, W. L., and R. L. Brown. 1982. Pheromones this group will be considered in a future work and evolutionary relationships of Tor tr icidae Annu Rev Ecol Syst 13: 395-422 Roelofs, W. L., and R. T. Card&. 1974. Sex phero- Acknowledgment mones in the revroductive isolation of lewidowterous species, pp 96-114 In M C Birch [id 1, hero- We thank R S Vetter for rearing the mones North Holland, Amsterdam. Ryan, T. A. 1960. Significance- tests for multiole com- References Cited par isons of proportions, variances, and other statis- tics Psycho1 Bull 57: 318-328 Card6, R. T., and T. C. Baker. 1984. Sexual com- Sower, L. L., K. W. Vick, and J. H. Tumlinson. 1974. munication with pheromones, pp 355-383 In W J (Z,E)-9,12-Tetradecadien-1-01:a chemical released Bell and R T Card6 [eds 1, Chemical ecology of in- by female Plodia interpunctella that inhibits the sex sects Chapman & Hall, New York pheromone response of male Cadra cautella Envi- Card&, R. T., A. M. Card&,A. S. Hill, and W. L. Roe- ion Entomol 3: 120 lofs. 1977. Sex pheromone specificity as a repro- Strong, R. G., J. Partida, and D. N. Warner. 1968. ductive isolating mechanism among the sibling species Rearing stor ed-pi oduct insects for labor ator y studies: Archips argyrospilus and A mortuanus and other six species of moths J Econ Entomol 61: 1237- sympatr ic tortr icine moths (Lepidoptera: Tor ti ici- 1249 dae) J Chem Ecol 3: 71-84 Thornhill, R., and J. Alcock. 1983. The evolution of Dobzhansky, T. 1940. Speciation as a stage in evo- mating systems Harvard University, Cam- lutionary divergence Am Nat 74: 312-321 bridge, Mass Ganyard, M. C., and U. E. Brady. 1971. Inhibition Vick, K. W., J. A. Coffelt, and R. W. Mankin. 1981. of attraction and cross-attraction by interspecific sex Recent developments in the use of pheromones to pheromone communication in Lepidoptera Nature monitor Plodia interpunctella and Ephestia cautel- (London) 234: 415-416 la, pp 19-28 In E R Mitchell [ed 1, Management 1972. Interspecific attraction in Lepidoptera in the of insect pests with semiochemicals Plenum, New field Ann Entomol Soc Am 65: 1279-1282 Yor k Grant, G. G., E. B. Smithwick, and U. E. Brady. 1975. West-Eberhard, M. J. 1983. Sexual selection, social Courtship behavior of phycitid moths I1 Behavioral competition, and speciation Q Rev Biol 58: 155- and pheromonal isolation of Plodia interpunctella 183 and Cadra cautella in the laboratory Can J Zoo1 53: 827-832 Received jov publication 17 October 1985, accepted Greenfield, M. D., and M. G. Karandinos. 1979. Re- 24 December 1985 source partioning of the sex communication channel in clearwing moths (Lepidoptera: Sesiidae) of Wis- consin Ecol Monogr 49: 403-426