马铃薯块茎蛾的交配行为

在温度为(24±2)℃、光周期为L∶D=14∶10、相对湿度为50%～70%环境条件下观察了马铃薯块茎蛾Phthorimaea operculella(Zeller)交配行为。结果表明,1～2日龄、3～4日龄成虫交配高峰期分别发生在进入暗期后的8.0～10.0h、6.5～8.0h内。两性交配率随日龄的增加显著下降。马铃薯块茎蛾雄成虫具有多次交配能力,在连续发生2次以上行为交配时会导致雄蛾有效交配率下降。雄蛾平均有效交配次数可达3.8次/头,最高达6次。增加雄性比例不会显著提高单雌产卵量,但将性比(♀:♂)由1∶1升至2∶1时即可显著降低单雌产卵量。     

二化螟的多次交配及其对雌蛾产卵量的影响

【目的】利用性诱防控和监测水稻二化螟Chilo suppressalis的有效性在田间已经得到认可。但雄蛾具有多次交配能力,致使性诱防治二化螟的应用策略一直存在争论。本研究的目的是探索二化螟雄蛾的多次交配及其对雌蛾繁殖力的影响,认识性诱防控害虫的机理。【方法】利用行为学方法调查了雌雄蛾以不同比例配对(1∶1, 4∶1和10∶10)时雄蛾的交配次数和交配持续时间,并结合解剖学方法,观察分析了二化螟雄蛾的交配次数对精巢、交配囊和精包大小以及雌蛾产卵量的影响。【结果】二化螟雌雄蛾按1∶1配对时,交配雄蛾和多次交配雄蛾的比例分别为74.0%和36.0%,平均交配1.7次,首次交配主要发生在0-1日龄,绝大部分具有多次交配能力的雄蛾的首次交配发生在0-1日龄。雌雄蛾按4∶1配对时,交配雄蛾和多次交配雄蛾的比例分别为69.4%和51.3%,平均交配2.1次,显著高于按1∶1配对。雌雄蛾按10∶10配对时,交配雄蛾和多次交配雄蛾的比例分别为65.5%和37.8%,平均交配1.9次。雄蛾第3次交配的持续时间显著长于第1和2次交配,但是交配1-3次雄蛾的精巢体积无显著差异。与不同交配次数雄蛾进行交配的雌蛾交配囊和精包体积无显著差异,雌蛾产卵量也无显著差异。【结论】二化螟中仅有部分雄蛾能够多次交配,多次交配雄蛾的首次交配主要发生在0-1日龄,部分雄蛾一生都不会交配。研究结果为二化螟的性诱防治提供了理论依据。     

性比对草地螟生殖潜力和寿命的影响

【目的】探明性比对草地螟Loxostege sticticalis L.种群繁殖的影响,为预测预报提供科学指导。【方法】室内条件(温度(22±1℃,相对湿度70%±5%,光周期16L︰8D)下,研究了草地螟成虫雌雄比例(♀︰♂=1︰3,1︰2,1︰1,2︰1,3︰1)对主要繁殖参数和寿命的影响。【结果】草地螟成虫的产卵前期随着雌蛾比例的增大而延长;性比为1︰1时雌蛾的产卵同步性最高;雌蛾的交配次数、产卵量以及最终孵出的后代幼虫量在不同性比组之间差异变化不大,而雄蛾的交配次数、对后代的贡献量却随着雌蛾比例的加大而显著增加,而当雌雄比为3︰1时,雌雄蛾的寿命均显著下降;在雌雄比为3︰1的条件下,雄蛾的交配次数以及对后代的贡献量均为雌蛾的2倍左右。【结论】性比对草地螟雌蛾生殖影响较小,而对雄蛾生殖的影响较大。在雌成虫比例较低(性比为1︰3)的情况下,雄成虫的交配和生殖能力不能得到充分发挥,进而造成种群生殖资源的浪费。根据雌雄成虫交配潜力及对后代贡献量的比较分析,可以推测性比为2︰1至1︰1时,有利于草地螟大发生种群的形成。     

小木蠹蛾性行为和性信息素产生与释放的时辰节律

观察了小木蠹蛾Holcocerus insularis的性行为反应,并采用腺体提取、空气收集 、触角电位和田间试验等方法对雌蛾产生和释放性信息素的时辰节律进行了研究。结果表明： (1) 该虫羽化24 h后性成熟,婚飞和交配活动主要在1：00～4：00,交配历时15～45 min;(2) 大部分雌蛾一生交配1～3次,雄蛾多数一生只交配1次,雌雄比为1∶0.89; (3) 雌蛾腺体提取物中性信息素含量同蛾龄有关,2日龄雌蛾腺体性信息素含量最高;(4) 雌蛾腺体中性信息素含量在1：00时最高,而性信息素释放高峰在2：30。     

栎黄枯叶蛾羽化及生殖行为研究

栎黄枯叶蛾Trabala vishnou gigantina Yang是近年在沙棘(Hippophae rhamnoides)林中大面积暴发的一种食叶害虫。通过野外调查和室内饲养观察相结合对该虫的羽化、交配和产卵等行为等进行了研究。结果表明,栎黄枯叶蛾羽化期40 d左右,羽化高峰期为9月上旬,日羽化高峰出现在傍晚17:00—23:00,占全天羽化量的82.46%;雌雄性比为1∶1.41;交配高峰期发生在凌晨3:00—4:00,成虫羽化翌日开始进行交尾,2日龄雌蛾交配率最高,达到45.6%,随后交配率逐步降低。雌蛾一生只交尾1次,雄蛾可进行多次交尾。成虫交配持续时间多为14¹6 h。成虫交配后即可产卵,产卵主要在夜间进行,产卵高峰期在2:00—6:00,占全天产卵量的82.40%。未交配雌蛾和雄蛾的平均寿命为11.05 d和9.85 d;显著高于已交配雌蛾和雄蛾的8.05 d和7.35 d,说明交配可明显缩短雌雄成虫寿命。     

甜菜夜蛾交配行为和能力

在(27±1)℃,光周期L14∶D10的条件下对甜菜夜蛾I>Spodoptera exigua的交配行为及能力进行了研究。结果表明：成虫在羽化当晚即可进行交配,交配率以羽化后头三个晚上的较高(>82%),但从第4天起则显著下降。成虫一天中的交配时间出现于23:30～05:30之间,交配高峰出现在01:30～02:30和03:00～04:00 之间, 其中以第1高峰的发生频率较高。成虫交配持续时间从22～191 min不等,但以30～60 min的为多(40.8%, n=97), 60～90 min的次之(19.4%),超过180 min的较少(10.2 %)。另外,交配持续时间与蛾龄紧密相关。蛾龄越大,交配持续的时间越长,且差异显著。雄蛾一生的交配能力由1～11次不等,但受性比的影响显著：在性比为1∶1的条件下,雄蛾平均交配次数仅为3.0 次,而在2♀∶1♂至5♀∶1♂时,则增加到5.1～6.0 次。雌蛾交配比例及次数受性比的影响也很大：没有交配的雌蛾比例从1∶1时的8.3%增加到5♀∶1♂时的32%,仅交配一次的比例从16.7%增加到38.7%,而交配≥5 次的比例则从 25%下降到0。最后,对这些结果在甜菜夜蛾防治中应用的可能性进行了讨论。     

水稻二化螟的交配行为

在室内条件下,对水稻二化螟Chilo suppressalis的交配行为及能力进行了研究.结果表明：大多数二化螟雌蛾一生只交配一次,平均0.92次;而雄蛾具有多次交配能力,最多达4次,平均2.72次.二化螟雌蛾的日龄影响其交配率、交配起始时间和持续时间,随二化螟雌蛾日龄的增加,其交配率逐渐下降,交配起始时间逐渐提前,而交配持续时间逐渐上升.相反,二化螟雄蛾日龄对其交配率、交配起始时间和持续时间没有明显影响.交配日龄对二化螟雌蛾的生殖力也存在显著影响,随着二化螟雌蛾交配日龄的增加,雌蛾产卵量下降,卵孵化率降低,产卵期缩短,它们都与雌蛾交配日龄存在显著的负相关;而雌蛾产卵前期和雌蛾寿命随雌蛾交配日龄的增加而延长,与雌蛾交配日龄存在显著的正相关.但二化螟雄蛾交配日龄对雌蛾的生殖力没有明显影响,二化螟雄蛾一生都具有较强的交配繁殖能力.同时,不同交配史的雄蛾与雌蛾交配,对雌蛾的生殖力也没有显著影响.表明二化螟的交配活动是由雌蛾主导控制的.最后,对这些结果在二化螟性信息素防治中应用的可行性进行了探讨.在应用性信息素控制二化螟的实践中,可以在两方面取得实效,一是性信息素可以阻碍雌雄之间正常交配,降低交配率;二是可以推迟二化螟雌虫的交配,使其产卵量和卵孵化率降低.     

棉铃虫成虫对性信息素的电生理和行为反应研究

通过EAG和风洞实验,研究了棉铃虫雌雄成虫对性信息素组分和诱芯(Z-11-16Ald∶Z-9-16Ald=97∶3)的电生理反应。其中棉铃虫雌、雄蛾对诱芯的平均EAG反应测定值分别为1.06mV和4.32mV,分别高出对照(无性信息素空白诱芯)0.67mV和0.366mV,差异均达到极显著水平(雌蛾：t＝25.020, P≤0.01;雄蛾：t＝44.269,P≤0.01);棉铃虫雌蛾对性信息素组分(Z-11-16-Ald和Z-9.16Ald)的EAG反应值随浓度增加而增加;雄蛾在被剪除触角后与雌蛾不能正常交配,而雌蛾在被剪除触角后仍有40%的交配率,比正常雌雄蛾的交配率(70%)有所下降;在风洞实验中,雄蛾没有顺风远离诱源的飞行行为,趋向诱源的比率为81.8%,与对照有显著差异。研究表明性信息素组分对棉铃虫的交配活动有明显的影响。     

酪蝇交配行为和能力

在(27±1)℃,光周期L∶D=12∶12的条件下对酪蝇Piophila casei L.交配行为及能力进行了研究。结果表明,雌虫在羽化1min后即可交配,而雄虫在羽化30min后进行交配。进一步观察结果表明,羽化后80min的两性成虫交配率最高(90%),成虫一天之中的交配高峰期出现在10∶00—11∶00,次高峰出现在11∶00—12∶00。两性交配持续时间从4～9min不等,以5min为最多(43.3%),6min次之(23.3%)。一般情况下,雌虫一生只交配1次,雄虫从1～7次不等,但以2次为最多(45%),3次的次之(20%)。     

二化螟雄蛾交配行为与精巢大小的关系

【目的】为了明确二化螟Chilo suppressalis雄蛾交配行为与精巢大小的关系,阐明信息素群集诱杀防治二化螟的有效性。【方法】本研究通过测定和比较不同日龄、交配状态以及性信息素诱捕的二化螟雄蛾精巢体积,建立精巢体积与雄蛾发育及交配状态的相关性。【结果】雄蛾日龄显著影响二化螟的交配,刚羽化(0日龄)雄蛾的交配率较低,1日龄雄蛾的交配率最高,之后随着日龄增加交配率逐渐降低。精巢体积与二化螟雄蛾日龄之间存在显著的负相关性。同一日龄交配的二化螟雄蛾的精巢体积显著大于未交配雄蛾;性诱捕器诱捕雄蛾的精巢体积显著大于未被性诱捕器诱捕雄蛾,与已交配雄蛾的精巢体积相似。交配之后,精巢的发育过程和未交配雄蛾相似。田间性信息素引诱二化螟雄蛾精巢体积小于0-1日龄未交配雄蛾,大于2-6日龄未交配雄蛾。【结论】本研究结果表明,二化螟雄蛾对雌蛾性信息素的反应与其精巢大小存在正相关性;性信息素引诱的二化螟雄蛾具有更强的性信息素反应能力,同时性信息素引诱的大部分雄蛾为未交配状态;交配过程并不影响二化螟雄蛾精巢体积,也不影响精巢发育。二化螟交配能力与精巢大小的关系在理论上解释了性信息素群集诱杀二化螟的防控有效性,并为其他蛾类昆虫的交配研究提供依据。     

亚洲玉米螟交配率和交配次数与其日龄、性比和精巢大小的关系

【目的】昆虫交配行为与其日龄和生殖系统发育密切相关。本研究旨在明确亚洲玉米螟Ostrinia furnacalis交配行为与其日龄、性比和雄蛾精巢大小的关系,为性信息素群集诱杀和交配干扰防控亚洲玉米螟提供理论依据。【方法】通过室内交配实验测定了不同配对晚数、日龄、性比亚洲玉米螟的交配率和交配次数,通过雄蛾精巢解剖分析了交配次数与精巢体积的关系。【结果】亚洲玉米螟的交配率随配对晚数增加而增加,但第1-5晚的增加速度大于第6-7晚的;1-4日龄蛾的交配率随日龄增加而增加,5日龄蛾的交配率显著降低;1-3日龄蛾配对1晚的交配率与新羽化蛾配对2～4晚的均无显著差异。亚洲玉米螟可以交配1～3次,但是交配3次的比例极低。雌性数量从1增为2时,雄蛾的交配率显著增加;从2增为3时,雄蛾的交配率显著降低、死亡率显著增加,交配1次的雄蛾进行二次交配的比例也增加,并且雄蛾更愿意与处女雌蛾进行第2次交配;交配1次雄蛾的精巢体积总是显著大于同期未交配雄蛾的,交配1次稍降低了雄蛾精巢的衰退速度,交配2次则明显增加雄蛾精巢的衰退速度。【结论】本研究明确了亚洲玉米螟交配与日龄、性比和雄蛾精巢体积之间的关系,从理论上证实了性信息素群集诱杀技术和交配干扰技术防治亚洲玉米螟的有效性。     

Disruption of male spruce budworm orientation to female moths by pheromone and pheromone analogues in a wind tunnel

Abstract. The ability of male spruce budworm moths, Choristoneura fumiferana (Clem.), to orientate to and locate virgin female moths was investigated in a laboratory wind tunnel. When presented with two caged ‘target female’ moths, more than 99% of the male moths locked on and flew directly to the females. When confined for 3 h before release, downwind of a three-dimensional array of thirty-five evenly distributed female moths (a density of 40/m³), over 90% of the males still successfully oriented to one or another of the females, although not always to the target females. With an array of thirty-five septa containing either E-11-tetradecenyl acetate on E-11-tetradecenol there was no visible change in behaviour; >90% of the males flew directly to the two target females, which indicates that neither the acetate nor the alcohol has potential for mating disruption. An array of thirty-five septa containing a 955 blend of E- and Z-11-tetradecenal, the main components of the spruce budworm sex pheromone, significantly reduced the numbers of male moths able to locate the target females, and effects were concentration-dependent. The highest concentration, which gave a release rate similar to that of a calling female, produced the same level of disruption as the thirty-five females, but sensory fatigue became a factor in addition to ‘false trail following’. Lower concentrations were significantly less effective, with no evidence of sensory fatigue. At all concentrations significant numbers of males flew to the septa (false trail following), but when male moths were left uncaged in the tunnel for a further 3h, most eventually located the females. This suggests that false trail following alone will not prevent mating. The level of disruption was not improved by the addition of 2% tetradecanal to the 955 blend. Similar levels of disruption to the 955 blend were obtained with an 80:20 blend. A 5050 blend still caused a significant amount of false trail following, but less than the other blends. The ability of male spruce budworm to orientate to off-blend trails was enhanced if the males were first exposed to the natural, female-produced pheromone.     

Divergence in male mating tactics between two populations of the soapberry bug: I. Guarding versus nonguarding

I compared male allocation to prolonged mate guarding versusnot guarding between two populations of the soapberry bug (Jaderahaematoloma) that differ in adult sex ratio: Oklahoma, USA (mean± SD adult sex ratio, 2.70 ± 0.95 males per female),and Florida, USA (1.09 ± 0.26 males per female). To predictthe reproductive performance of each mating tactic in each population,I collected data on search time per mating, time required forguarding to be effective, sperm competition, female rematingpropensity, and female resistance to guarding. Search time alonediffered significantly between the populations, being much greaterin Oklahoma (estimated as 26.2 h per mate) than in Florida (estimatedas 9.6 h per mate). For males in each region, these data wereused to model the costs and benefits of guarding for differentnumbers of oviposition bouts versus not guarding. The reproductiverate of nonguarders in Oklahoma is exceeded by that of guarderswho remain with a female for more than one oviposition bout,but in Florida, the reproductive rate of nonguarders is onlyexceeded by that of guarders who remain with a female for atleast three ovipositions. Consistent with the model, Oklahomamales in field arenas guarded more frequently than did Floridamales. However, nonguarding was common in both populations,and guarding durations were highly variable.     

豆野螟成虫行为学特征及性信息素产生与释放节律

豆野螟Maruca vitrata (Fabricius)是一种严重的泛热带豆类蔬菜害虫。本文在（29±1）℃、相对湿度75%～80%、光周期14L∶10D条件下研究了豆野螟成虫的羽化、交尾行为以及雌蛾性信息素的释放节律。结果表明：其羽化行为全天可见,在雌蛾中,86%于暗期羽化; 在雄蛾中,73%于暗期羽化。雌雄蛾羽化行为在暗期第4、5和8 h差异达到显著 (t>4; P<0.05)。交尾活动发生在暗期19：00到5：00之间,交尾持续时间最短约为20 min,最长约为90 min,3日龄进入暗期第5 h具有最高的交尾率。1、6和7日龄成虫具有单个交尾高峰,2到5日龄成虫具有两个交尾高峰。同一日龄成虫交尾在暗期前半段平均花费的时间要明显高于在后半段花费的时间。低龄和高龄的成虫用于交尾的时间明显高于中龄的性成熟成虫。成虫的开始交尾时间随着日龄的增加逐渐前移。雄蛾对进入暗期后第5 h和第9 h处女雌蛾的性腺提取物和空气收集性信息素的触角电位反应最强,对 3日龄处女雌蛾的性腺提取物和空气收集性信息素的触角电位反应最强。处女雌蛾田间诱蛾试验表明：23：00-01：00为诱蛾高峰期,3日龄处女雌蛾的诱蛾效果最好。该蛾的羽化、交尾及性信息素产生与释放均存在节律上的一致性。雌蛾的性信息素释放的时间较长,见于整个暗期,然而交尾行为发生时间较短,主要发生于两个交尾高峰之间。     

Mating frequency in dispersing potato tuber moth, Phthorimaea operculella, and its influence on the design of refugia to manage resistance in Bt transgenic crops

Mating of potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), was investigated in relation to the dispersal of males in laboratory and field trials. The effect of stimulating the flight of males to light sources in a large cage on their mating ability was estimated for three age groups, and compared with similar estimates for confined moths. Although the mating of males declined with ages of up to 15 days, simulated dispersal had no effect on subsequent mating when the males were paired with virgin females. The dispersal of male moths was also categorised by the initial flight activity of untethered moths to a light source. Scores for poor, moderate, and good flight provided a repeatable measure of initial male flight activity, but the degree of activity was not related to their subsequent mating ability. In the field, virgin female potato tuber moths were tethered at various distances from the edge of isolated potato crops and then dissected to determine their mating status. Female mating frequency averaged 75% at the crop margin, remained above 50% up to 200 m, and then declined to 19% at 360 m from the margin. Derivation of the mating probability for an individual male potato tuber moth confirmed earlier work by other researchers that has indicated a tendency for dispersal prior to mating, and that males retain their ability to mate as they disperse from a crop. The influence of dispersal and mating on gene flow between crops, and its potential effects on refuge size required to minimise the development of resistance to Bt transgenic potato crops was examined.     

Effect of body size and larval experience on mate preference in Helicoverpa armigera (Hübner) (Lep., Noctuidae)

Abstract:  We studied the mating selection in the cotton bollworm, Helicoverpa armigera (Hübner), in relation to body size and larval diet in the laboratory. When provided with an artificial diet at larval stage, weight, body and forewing length did not affect the probability of a male/female moth being selected for mating, but the abdominal width of selected female moths was significantly wider than that of non-selected female moths. 30 female moths were dissected and number of eggs was counted after mating, and there was a correlation between the abdominal width and egg number. There was also significant difference of weight loss between selected and non-selected male/female moths after the mating. The effect of operational sex ratio on mating latency and copulation duration were tested, and the result indicated that mating latency of male selection was significantly longer than that of female selection, but the difference of copulation duration was not significant. Cotton, corn and peanut plants were provided to larvae to test the effect of larval host plant experience on mate choice. When cotton- and peanut-fed moth severed as potential partners, both female and male of cotton-fed moths significantly preferred cotton- to peanut-fed moths for mating. The possible reasons for mate preference based on larval host plant experience may account for host plants attributes on sex pheromone variation and sexual maturity. These findings may impact Bacillus thuringiensis resistance management.     

The role of heliothine hairpencil compounds in female Heliothis virescens (Lepidoptera: Noctuidae) behavior and mate acceptance

Studies on numerous insect species suggest that male-produced sex pheromones play a role in attracting females; as aphrodisiacs, making females more quiescent; or as a means of inhibiting competing males. Male heliothine moths display abdominal hairpencils during courtship, but the specific effects of the odors released on female behavior have not yet been elucidated. This study investigates the role of male hairpencil compounds in female Heliothis virescens mating behavior. Female H. virescens were exposed to filter paper loaded with hairpencil extracts of male H. virescens, Heliothis subflexa and Helicoverpa zea, and observed for behavioral responses to odors. Single synthetic compounds found in the H. virescens hairpencil blend were also tested. In mating assays between single male and female H. virescens it was found that: (i) antennectomized females mated less frequently than sham-operated females; (ii) females mated less frequently with males whose hairpencils had been surgically removed; (iii) females mated with males with ablated hairpencils if a filter paper loaded with one male equivalent of H. virescens hairpencil extract was presented simultaneously; and (iv) this effect was species-specific, as presentation of H. subflexa or H. zea hairpencil extracts did not restore mate acceptance. This study suggests that odors released by male hairpencils are important in mate acceptance by female H. virescens, and may play a role in mate choice and species isolation.     

Ecology of a bolas spider,Mastophora hutchinsoni: phenology,hunting tactics,and evidence for aggressive chemical mimicry

Summary Bolas spiders are relatively rare members of the large family known as orb weavers. Instead of using a typical web to capture prey, late-stadia and adult female bolas spiders swing a droplet of adhesive on a thread at flying insects. Mastophora hutchinsoni (Araneae: Araneidae) is one of five Mastophora species known from the United States and occurs over much of eastern North America. It is univoltine in Kentucky and overwinters in the egg stage. Spiderling emerged in May, the diminutive males matured in late June and early July, and females matured in early September. Eggs were produced from late September to late October or early November. This report is the first complete documentation of the population phenology of any bolas spider. Newly-emerged M. hutchinsoni spiderlings did not use a bolas, but instead hunted by positioning themselves on the underside of leaf margins where they ambushed small arthropods that crawled along the leaf margins. Subadult and adult female M. hutchinsoni used a bolas to capture moths. Only male moths were captured, specifically three species of Noctuidae (bristly cutworm, bronzed cutworm, and smoky tetanolita) and one species of Pyralidae (bluegrass webworm). Among 492 prey captured by more than twenty spiders at two sites during 1985 and 1986, smoky tetanolita moths and bristly cutworm moths accounted for 93% of the total. The flight behavior of approaching moths, the limited taxa caught from a large available moth fauna, and the fact that only males were caught support the hypothesis that the spider attracts its prey by producing chemicals which mimic the sex pheromones of these moth species. Adult female M. hutchinsoni frequently captured more than one moth species on a given night. The two most common prey species were active at different times of night, the bristly cutworm soon after nightfall and the smoky tetanolita generally between 11:00 p.m. and dawn. This pattern suggests that mating activity of these moth species may be temporally isolated, a common phenomenon when sympatric species have similar pheromones. If so, the spider could capture both species without producing different pheromone-mimicking compounds, simply by hunting during the activity period of each species.The investigation reported in this paper (No. 87-7-76) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director     

RETRACTED: WHAT DETERMINES SEX ROLES IN MATE SEARCHING?

In a seminal paper, Hammerstein and Parker (1987) described how sex roles in mate searching can be frequency dependent: the need for one sex to perform mate searching is diminished when the opposite sex takes on the greater searching effort. Intriguingly, this predicts that females are just as likely to search as males, despite a higher potential reproductive rate by the latter sex. This prediction, however, is not supported by data: male mate searching prevails in nature. Counterexamples also exist in the empirical literature. Depending on the taxon studied, female mate searching can arise in either low- or high-density conditions, and suggested explanations differ accordingly. We examine these puzzling observations by building two models (with and without sperm competition). When sperm competition is explicitly included, male mate searching becomes the dominant pattern; when it is excluded, male mate searching predominates only if we assume that costs of searching are higher for females. Consequently, two hypotheses emerge from our models. The multiple-mating hypothesis explains male searching on the basis of the ubiquity of sperm competition, and predicts that female searching can arise in low-density situations in which sperm can become limiting. It can also explain cases of female pheromone production, where males pay the majority of search costs. The sex-specific cost hypothesis predicts the opposite pattern of female searching in high-density conditions, and it potentially applies to some species in which sperm limitation is unlikely.