两种植绥螨的同类相残和集团内捕食作用

巴氏新小绥螨(Neoseiulus barkeri)和黄瓜新小绥螨(N.cucumeris)是两种多食性植绥螨,主要捕食叶螨和蓟马等,目前在我国广泛应用于农业生物防治中.本文研究了这两种植绥螨种内的同类相残(cannibalism)和种间的集团内捕食作用(intraguild predation)以及相互之间的攻击强度,以明确两者之间的相互关系,为合理构建天敌组合及评估生物防治的作用提供依据.结果显示:两种植绥螨对同种或异种幼螨的捕食量最大,其次是若螨,而对卵的捕食量极低.两种植绥螨对异种幼螨或若螨的捕食量均极显著高于对同种幼螨或若螨的捕食量.可见,无其他猎物存在情况下,两种植绥螨同时发生时更倾向于发生种间的集团内捕食.而巴氏新小绥螨对异种幼螨或若螨的捕食量均高于黄瓜新小绥螨对异种幼螨或若螨的捕食量,并且巴氏新小绥螨和黄瓜新小绥螨相比,巴氏新小绥螨对异种幼螨的攻击性更强,因此当这两种植绥螨发生集团内捕食时,巴氏新小绥螨是潜在的集团内捕食者,而黄瓜新小绥螨是潜在的集团内猎物.     

两种植绥螨种内和种间捕食及适合度

【目的】通过研究斯氏钝绥螨Amblyseius(Typhlodromips)swirskii和胡瓜新小绥螨Neoseiulus cucumeris这两种外来植绥螨种内和种间的捕食关系及适合度,为斯氏钝绥螨的释放应用前的风险评估及与胡瓜新小绥螨的联合释放技术提供理论依据。【方法】在无共享猎物的条件下,分别为两种雌成螨提供同种和异种的卵、同种和异种的幼螨、同种和异种的若螨,测定其对同种和异种不同个体的捕食选择性及捕食量,并比较两种植绥螨捕食后的适合度（产卵率和存活率）的差异。【结果】两种植绥螨互为捕食者,斯氏钝绥螨为集团内捕食者的几率高于胡瓜新小绥螨;两种植绥螨发生同类相残的几率无显著差异（χ²=0.118,df=1,P=0.732）。两种植绥螨对幼螨的捕食量显著高于对若螨、卵的捕食量（斯氏钝绥螨：F_(2,114)=66.27,P<0.0001;胡瓜新小绥螨：F_(2,114)=50.39,P<0.0001）,而且两种植绥螨对异种幼螨和若螨的捕食量均显著高于对同种个体的捕食量。两种植绥螨捕食幼螨后的产卵率均显著高于捕食若螨后的产卵率（斯氏钝绥螨：t=5.774,df=26,P<0.0001;胡瓜新小绥螨：t=3.334,df=26,P=0.0026）,斯氏钝绥螨捕食异种个体后的产卵率显著高于捕食同种个体后的产卵率（t=2.854,df=26,P=0.008 4）。两种植绥螨捕食不同发育阶段（幼螨和若螨）的存活率无显著差异;但斯氏钝绥螨捕食异种个体后的存活率显著高于捕食同种个体后的存活率（t=2.196,df=26,P=0.0372）。【结论】两种植绥螨更倾向于发生交互集团内捕食作用而非同类相残;两种植绥螨捕食幼螨比捕食若螨更利于产卵;对于斯氏钝绥螨,异种个体是比同种个体更适合的食物来源。     

以实验种群生命表评价六种植绥螨对西花蓟马的控制潜力

【目的】植绥螨是蓟马等害虫(螨)的重要捕食性天敌,在当前生物防治中应用广泛,本研究旨在为本地植绥螨资源的开发利用及筛选出控制西花蓟马Frankliniella occidentalis最有效的植绥螨天敌提供依据。【方法】以西花蓟马为猎物,在室内温度(25±1)℃、光照16L︰8D、相对湿度80%±5%的条件下,比较了内蒙古本地植绥螨种类有益真绥螨Euseius utilis Liang et Ke、苏氏副伦绥螨Paraseiulus soleiger Ribaga和巴氏新小绥螨Neoseiulus barkeri Hughes及目前应用的植绥螨斯氏钝绥螨Amblyseius swirskii Athias-Henriot、东方钝绥螨A.orientalis Ehara和黄瓜新小绥螨N.cucumeris Oudemans取食西花蓟马后的发育历期和生殖潜力,并组建了实验种群生命表以评价各类植绥螨的捕食潜能。【结果】有益真绥螨的日均产卵量(1.67±0.02)粒和黄瓜新小绥螨的日均产卵量(1.58±0.06)粒相近且无显著差异,仅次于斯氏钝绥螨(1.69±0.07)粒;有益真绥螨其子代雌雄性比与黄瓜新小绥螨的性比也相同(1.63︰1),低于斯氏钝绥螨(1.77︰1)和巴氏新小绥螨(1.64︰1);有益真绥螨的世代平均周期最短(T=19.36 d),内禀增长率(rm=0.16)和周限增长率(λ=1.17)均最大,种群倍增时间最短(t=4.33 d)。【结论】有益真绥螨以西花蓟马为食后种群数量增长的潜力强于其他5种植绥螨,是本地防治西花蓟马较有潜力的植绥螨种类。     

加州新小绥螨和巴氏新小绥螨对二斑叶螨的捕食能力比较

【目的】比较加州新小绥螨Neoseiulus californicus和巴氏新小绥螨Neoseiulus barkeri对二斑叶螨Tetranychus urticae的捕食能力,为果园二斑叶螨生物防治剂的选择提供依据。【方法】采用捕食功能反应的方法研究加州新小绥螨和巴氏新小绥螨雌成螨对二斑叶螨各螨态的捕食作用。【结果】加州新小绥螨和巴氏新小绥螨雌成螨对二斑叶螨各螨态的捕食功能反应均属于HollingⅡ型,对二斑叶螨各螨态的捕食能力均随着螨态的增大而降低,对卵的捕食能力最强,其次是幼螨、第一若螨、第二若螨、成螨。巴氏新小绥螨对二斑叶螨卵、幼螨的捕食能力强于加州新小绥螨,功能反应参数a/Th值分别高出55.2%和30.1%,而加州新小绥螨对二斑叶螨第一若螨、第二若螨的捕食能力强于巴氏新小绥螨,a/Th值分别高出67.5%和114.5%,两种捕食螨对二斑叶螨雌成螨的捕食能力相当,a/Th值均为4.5。加州新小绥螨和巴氏新小绥螨均对二斑叶螨的卵和幼螨表现出嗜食性,而对若螨和成螨没有嗜食性。两种捕食螨对二斑叶螨的捕食存在种内干扰,加州新小绥螨的干扰系数(0.328)大于巴氏新小绥螨(0.324)。【结论】在室内环境稳定的条件下,加州新小绥螨对二斑叶螨的捕食能力强于巴氏新小绥螨。     

不同猎物及密度对巴氏新小绥螨和拉戈钝绥螨同类相残和集团内捕食作用的影响

明确不同猎物及密度下巴氏新小绥螨Neoseiulus barkeri与拉戈钝绥螨Amblyseius largoensis(Muma)的同类相残和集团内捕食作用,为其协同应用控制橡胶树害螨提供依据.在室温27±1℃、湿度75％±5％、光周期12 L∶12D 条件下,以六点始叶螨 Eotetranvchus sexmaculatus(Riley)、比哈小爪螨Oligonychus biharen(Hirst)和东方真叶螨Eutetranychus orientalis(klein)为集团外猎物,观察巴氏新小绥螨和拉戈钝绥螨对集团内和集团外猎物的捕食选择行为,以及不同集团外猎物密度下两种捕食螨对同种和异种捕食螨的捕食作用.巴氏新小绥螨和拉戈钝绥螨对异种个体及集团外不同猎物的捕食偏好性及捕食时间存在明显差异.巴氏新小绥螨偏好取食集团外猎物,异种捕食螨拉戈钝绥螨残存率达到80.00％以上;拉戈钝绥螨偏好取食集团外猎物六点始叶螨和比哈小爪螨,而当东方真叶螨存在时,其更偏好取食异种捕食螨巴氏新小绥螨(残存率为26.67％);发生集团内捕食时,拉戈钝绥螨为集团内捕食者,而巴氏新小绥螨为集团内猎物.集团外猎物密度可显著影响巴氏新小绥螨和拉戈钝绥螨相残作用,尤以猎物六点始叶螨对巴氏新小绥螨和东方真叶螨对拉戈钝绥螨影响最为明显,其充足时比无猎物时捕食量分别下降了 68.85％和62.90％.巴氏新小绥螨和拉戈钝绥螨的集团内捕食分别以比哈小爪螨和六点始叶螨的影响最大,猎物充足时比无猎物时捕食量下降了 80.00％和69.44％,但拉戈钝绥螨在以东方真叶螨为猎物时集团内捕食受猎物密度影响较小,猎物充足时取食量与猎物不足时接近,比无猎物时捕食量只下降20.83％.集团外猎物六点始叶螨、比哈小爪螨存在时,巴氏新小绥螨和拉戈钝绥螨表现为偏好选择集团外猎物,密度增加对两种植绥螨的同类相残和集团内捕食作用有明显抑制作用,但东方真叶螨充足与否,拉戈钝绥螨对巴氏新小绥螨的集团内捕食作用影响差异不显著.     

双尾新小绥螨的形态特征及捕食性功能

【目的】通过对新疆本地捕食螨双尾新小绥螨Neoseiulus bicaudus Wainstein的形态学特征观察及其对新疆农作物上两种重要害螨的捕食量测定,为该捕食螨的保护、研究、扩繁和释放提供理论基础。【方法】在实验室(26±1)℃,RH60%,16L︰8D条件下,借助显微成像系统观察其各个螨态形态特征及生物学习性;定量小室饲养技术对不同密度下对新疆两种重要害螨各螨态的捕食量进行研究。【结果】双尾新小绥螨有卵、幼螨、第一若螨、第二若螨和成螨5个螨态,嗜好阴暗条件,活动范围小,通过有性生殖进行繁殖,有多次交配行为,产卵方式为单产;单头双尾新小绥螨雌成螨每日对截形叶螨Tetranychus truncatus卵和幼螨的捕食量(106.8粒/日·雌和45.4头/日·雌)要显著大于土耳其斯坦叶螨Tetranychus turkestani(64.4粒/日·雌和39.4头/日·雌),而对两种叶螨的若螨和成螨捕食量无明显差异。【结论】本研究表明双尾新小绥螨对土耳其斯坦叶螨和截形叶螨的卵和幼螨的捕食较对若螨和成螨的效果好,对新疆害螨有一定控制能力。     

巴氏新小绥螨毒死蜱抗性选育及生物学特性

【目的】明确巴氏新小绥螨Neoseiulus barkeri毒死蜱抗性对其生物学特性的影响,为抗药性捕食螨田间应用提供理论基础。【方法】在室内采用药膜法测定毒死蜱对巴氏新小绥螨的毒力,以半致死浓度(lethal medium concentration, LC₅₀)为选择压力,对巴氏新小绥螨敏感种群进行逐代汰选。应用生命表法分析毒死蜱抗性获得对巴氏新小绥螨相对适合度(relative fitness, Rf)的影响。采用HollingII模型拟合分析不同温度下巴氏新小绥螨毒死蜱敏感和抗性品系对柑橘全爪螨Panonychus citri卵和雌成螨捕食功能反应差异。【结果】经过21代抗性筛选,获得了抗性倍数为34.77倍的巴氏新小绥螨毒死蜱抗性品系。抗性获得对巴氏新小绥螨各发育历期、子代雌性比例和捕食功能反应等特征均无明显影响,但产卵期和雌成螨寿命有所缩短。在15℃时,巴氏新小绥螨敏感品系和抗性品系均无法完成整个世代周期。在25℃条件下,巴氏新小绥螨敏感品系和抗性品系的单雌产卵量均最高,分别为41.64±1.04和38.80±0.93粒/雌,两者差异显著;该温度条件下,巴氏新小绥螨敏感品系和抗性品系的产卵期均最长,分别为24.82±1.50和21.34±1.26 d,两者也存在显著性差异。在30℃条件下,巴氏新小绥螨敏感品系和抗性品系世代周期均最短,分别为6.62±0.23和6.53±0.13 d。同时,该温度条件下,巴氏新小绥螨敏感品系和抗性品系对柑橘全爪螨的捕食能力均最强,其中对卵的最大日捕食量分别为156.25和140.85粒,对雌成螨的最大日捕食量分别为23.10和22.32头。就相对适合度而言,巴氏新小绥螨抗性品系的相对适合度在25和30℃时略低于敏感品系,但在20和35℃时略高于敏感品系。【结论】总体而言,巴氏新小绥螨毒死蜱抗性获得对其在不同温度条件下生物学特性的影响较小。研究结果为巴氏新小绥螨抗性品系筛选及田间应用提供了理论依据。     

不同猎物及密度对巴氏新小绥螨和拉戈钝绥螨同类相残和集团内捕食作用的影响

明确不同猎物及密度下巴氏新小绥螨Neoseiulus barkeri与拉戈钝绥螨Amblyseius largoensis(Muma)的同类相残和集团内捕食作用,为其协同应用控制橡胶树害螨提供依据。在室温27±1℃、湿度75%±5%、光周期12 L:12 D条件下,以六点始叶螨Eotetranvchus sexmaculatus(Riley)、比哈小爪螨Oligonychus biharen(Hirst)和东方真叶螨Eutetranychus orientalis(klein)为集团外猎物,观察巴氏新小绥螨和拉戈钝绥螨对集团内和集团外猎物的捕食选择行为,以及不同集团外猎物密度下两种捕食螨对同种和异种捕食螨的捕食作用。巴氏新小绥螨和拉戈钝绥螨对异种个体及集团外不同猎物的捕食偏好性及捕食时间存在明显差异。巴氏新小绥螨偏好取食集团外猎物,异种捕食螨拉戈钝绥螨残存率达到80.00%以上;拉戈钝绥螨偏好取食集团外猎物六点始叶螨和比哈小爪螨,而当东方真叶螨存在时,其更偏好取食异种捕食螨巴氏新小绥螨(残存率为26.67%);发生集团内捕食时,拉戈钝绥螨为集团内捕食者,而巴氏新小绥螨为集团内猎物。集团外猎物密度可显著影响巴氏新小绥螨和拉戈钝绥螨相残作用,尤以猎物六点始叶螨对巴氏新小绥螨和东方真叶螨对拉戈钝绥螨影响最为明显,其充足时比无猎物时捕食量分别下降了68.85%和62.90%。巴氏新小绥螨和拉戈钝绥螨的集团内捕食分别以比哈小爪螨和六点始叶螨的影响最大,猎物充足时比无猎物时捕食量下降了80.00%和69.44%,但拉戈钝绥螨在以东方真叶螨为猎物时集团内捕食受猎物密度影响较小,猎物充足时取食量与猎物不足时接近,比无猎物时捕食量只下降20.83%。集团外猎物六点始叶螨、比哈小爪螨存在时,巴氏新小绥螨和拉戈钝绥螨表现为偏好选择集团外猎物,密度增加对两种植绥螨的同类相残和集团内捕食作用有明显抑制作用,但东方真叶螨充足与否,拉戈钝绥螨对巴氏新小绥螨的集团内捕食作用影响差异不显著。     

巴氏新小绥螨对同一栖息地枸杞瘿螨的捕食功能反应

枸杞瘿螨Aceria pallida Keifer（Acari: Eriophyoidae）是枸杞上为害最严重的有害生物之一。近期在内蒙古地区发现植绥螨巴氏新小绥螨Neoseiulus barkeri Hughes（Acari: Phytoseiidae）与枸杞瘿螨可同时发生在野生枸杞上。为评价巴氏新小绥螨对枸杞瘿螨的捕食潜力,本研究在室内25±1℃、RH 65%±10%、16 L∶8 D的条件下,研究了巴氏新小绥螨对不同密度枸杞瘿螨成螨（30、50、70、90、110、130、150、170头）的捕食功能反应及搜寻效应。结果表明,巴氏新小绥螨的雌、雄成螨对枸杞瘿螨成螨的捕食功能反应均为Holling-II型,即巴氏新小绥螨雌、雄成螨的捕食量随着猎物密度的增加而增加,一直到猎物密度较高时趋于稳定;而巴氏新小绥螨雌、雄成螨的搜寻效应随着猎物密度的增加而降低。巴氏新小绥螨雌成螨对相同密度下的枸杞瘿螨成螨的捕食量均高于雄成螨,而且雌成螨的搜寻效应也强于雄成螨。巴氏新小绥螨雌成螨的攻击率（α=4.4121）高于雄成螨（α=2.4403）,而雌成螨的处理时间（Th =0.0094 d）短于雄成螨（Th=0.0196 d）;雌、雄成螨的理论最大日捕食量（T/Th）分别为106.61头和51.02头。研究结果显示巴氏新小绥螨对枸杞瘿螨有较好的捕食潜力,性别对巴氏新小绥螨捕食枸杞瘿螨的功能反应有显著影响。     

加州新小绥螨在不同温度下对 六点始叶螨的捕食效能

为明确加州新小绥螨对橡胶六点始叶螨的控害潜能,系统研究了21℃、24℃、27℃、30℃、33℃5个不同温度条件下加州新小绥螨对六点始叶螨各螨态的捕食效能和自身密度干扰效应。结果表明:加州新小绥螨对六点始叶螨若螨、幼螨和卵的选择系数分别为0.71、1.75和0.54。在21℃～33℃条件下,加州新小绥螨对不同螨态六点始叶螨的功能反应均能很好地拟合Holling-II型圆盘方程,其对六点始叶螨雌成螨、若螨、幼螨的捕食效能(a/Th)在30℃时最强,分别达19.91、44.90、189.45头/d,对叶螨卵的捕食能力在不同温度间差异不显著。在同一温度条件下,加州新小绥螨对不同螨态六点始叶螨的捕食量大小依次为:幼螨若螨成螨卵。在相同的猎物密度条件下,加州新小绥螨的捕食作用率随其自身密度的增加而逐渐降低,说明加州新小绥螨存在种内竞争和自我干扰作用,自身干扰系数为0.349。     

Cannibalism and Intraguild Predation Among Phytoseiid Mites: Are Aggressiveness and Prey Preference Related to Diet Specialization?

We tested whether specialist and generalist phytoseiid mites differ in aggressiveness and prey choice in cannibalism and intraguild predation. Specialists tested were Galendromus occidentalis, Neoseiulus longispinosus, Phytoseiulus persimilis, and P. macropilis; tested were Amblyseius andersoni, Euseius finlandicus, E. hibisci, Kampimodromus aberrans, Neoseiulus barkeri, N. californicus, N. cucumeris, N. fallacis, and Typhlodromus pyri. Aggressiveness of cannibalistic females against larvae was not related to diet specialization except that highly aggressive species were exclusively generalists. Seldom to moderately cannibalizing species occurred in both generalist and specialist phytoseiids. In contrast to aggressiveness in cannibalism, generalists and specialists differed in aggressiveness in intraguild predation. Adult females of specialists were only slightly aggressive against heterospecific larvae, whereas adult females of all generalists except T. pyri were highly aggressive. Adult females of generalists were able to discriminate between con- and heterospecific larvae and preferentially consumed the latter when given a choice. Adult females of specialists except G. occidentalis showed no preference when given a choice between con- and heterospecific larvae. We conclude that aggressiveness in intraguild predation, species recognition and subsequent preferential consumption of heterospecifics when given a choice is common in generalist but not specialist phytoseiids. We discuss the evolutionary pathways that might have led to the difference between specialists and generalists in species discrimination.     

Nutritional benefits of intraguild predation and cannibalism among generalist and specialist phytoseiid mites

1. Intraguild predation and cannibalism are common among predaceous phytoseiid mites (Acari, Phytoseiidae) but the nutritional benefits gained by these processes are poorly understood. 2. The study reported here addressed the questions of whether cannibalism and intraguild predation provide different nutritional benefits and whether the ability to utilise cannibalism and intraguild predation is linked to the diet specialisation of phytoseiid mites. Specialists tested were Phytoseiulus macropilis, Galendromus occidentalis, and Neoseiulus longispinosus; generalists tested were Amblyseius andersoni, Neoseiulus cucumeris, and Neoseiulus fallacis. 3. All generalists and the specialist P. macropilis were able to complete juvenile development with both con‐ and hetero‐specific prey. Juvenile development of generalists was shorter with heterospecific prey than with conspecific prey, whereas development of the specialist P. macropilis did not differ between prey types. Only a few N. longispinosus and G. occidentalis, both specialists, reached adulthood by cannibalism but none reached adulthood by intraguild predation. 4. All generalists were able to sustain oviposition by intraguild predation. Neoseiulus cucumeris and A. andersoni laid more eggs with heterospecific prey than with conspecific prey, whereas N. fallacis had similar oviposition rates with both prey types. No specialist sustained oviposition by intraguild predation or cannibalism. 5. Overall, generalists gained equal or more nutritional benefits by intraguild predation than by cannibalism and were able to utilise phytoseiid intraguild prey as an alternative food source. Specialists gained equal or more nutritional benefits from cannibalism than from intraguild predation. For specialists, con‐ and hetero‐specific phytoseiids may be considered only a supplemental food.     

Risk assessment of non-target effects caused by releasing two exotic phytoseiid mites in Japan: can an indigenous phytoseiid mite become IG prey?

Two exotic phytoseiid mites, Neoseiulus cucumeris and Amblyseius swirskii, are commercially available in Japan for the control of thrips and other pest insects. As part of a risk assessment of the non-target effects of releasing these two species, we investigated intraguild predation (IGP) between these exotic phytoseiid mites and an indigenous phytoseiid mite Gynaeseius liturivorus, which is promising as an indigenous natural enemy for the control of thrips in Japan. To understand IGP relations between the exotic and indigenous phytoseiid mites after use of the exotic mites for biological control, we investigated IGP between them in the absence of their shared prey. When an IG prey was offered to an IG predator, both exotic and indigenous females consumed the IG prey at all immature stages (egg, larva, protonymph, deutonymph), especially at its larval stages. The propensity for IGP in a no-choice test was measured by the survival time of IG prey corrected using the survival time of thrips offered to the IG predator. There was no significant difference in the propensity for IGP between N. cucumeris and G. liturivorus, but the propensity was significantly higher in A. swirskii than G. liturivorus. The propensity for IGP in a choice test was measured by the prey choice of the IG predator when a conspecific and a heterospecific larva were offered simultaneously as IG prey. Both exotic females consumed the heterospecific larva only. The indigenous female preferentially consumed the heterospecific larva when the heterospecific larva was N. cucumeris, but consumed the conspecific larva when the heterospecific larva was A. swirskii. We concluded that further investigation would be necessary for the exotic mites’ risk assessment, since the propensity for IGP of the two exotic females was similar to or higher than that of the indigenous female in both the no-choice and choice tests.     

Females as intraguild predators of males in cross-pairing experiments with phytoseiid mites

Studies on intraguild interactions between phytoseiid species have shown that intraguild predation occurs and is most commonly manifested as adult females of one species feeding on juveniles of another. Whether such intraguild interactions can also occur between adult females of one species and adult males of another, is not known. Herein, we report on intraguild interactions between adults of the two sexes in cross-pairing experiments involving three related phytoseiid species (Neoseiulus paspalivorus, N. baraki and N. neobaraki) that are potential candidates for controlling the coconut mite Aceria guerreronis, a serious pest of coconut palms in tropical countries. For comparative reasons, the experiments were repeated with larvae instead of males, and with only males or only females of two different species together. In the presence of an ample supply of prey, females of N. neobaraki never fed on individuals of their own species, yet appeared to be very aggressive against males, as well as larvae of the other two phytoseiid species. They also fed on females of N. paspalivorus, but rarely on females of N. baraki. Males of N. neobaraki did not suffer mortality when together with females of either of the two other phytoseiid species. Males of N. baraki did not suffer predation from females of N. paspalivorus, but males of N. paspalivorus suffered some mortality (15 %) from N. baraki females. Larvae of each of the three species were vulnerable to intraguild predation by heterospecific adult females, except for N. neobaraki larvae when together with N. baraki females. The absence or presence of intraguild predation is largely explained by the size ratios of the individuals that were put together: large individuals feed on smaller ones, but never the reverse. For each sex, size declines in the following order: N. neobaraki > N. baraki > N. paspalivorus. Moreover, for each species, females are larger than males and males are larger than larvae. Strikingly, however, females did not kill males and larvae of their own species. We propose that niche competition between related phytoseiid species is not only determined by intraguild predation on heterospecific larvae, but also by imposing great mortality on males from the intraguild prey because phytoseiid females being pseudo-arrhenotokous require insemination to produce offspring of both sexes.     

Predation preferences and discrimination between con- and heterospecific prey by the phytoseiid mites Phytoseiulus persimilis and Neoseiulus californicus

Discrimination between and predation preference for con- or heterospecific larvae was examined for adult females of P. persimilis and N. californicus in plexiglass cages with and without their primary prey T. urticae. Rates of intra- and interspecific predation on larvae were measured for females held on leaves and provided with excess amounts of spider mites. Females of the generalist N. californicus distinguished con- and heterospecific larvae and preferred to prey upon the latter. Females of the specialist P. persimilis appeared to lack discrimination ability and fed equally on con- and heterospecifics. When spider mites and phytoseiids were offered simultaneously, all P. persimilis females chose to first attack T. urticae, whereas N. californicus females attacked both tetranychids and heterospecific phytoseiids. Females of both predators preyed upon phytoseiid larvae when held on leaves with surplus T. urticae: while P. persimilis fed on both con- and heterospecifics, N. californicus attacked larvae of P. persimilis but avoided cannibalizing larvae. The different behaviors of P. persimilis and N. californicus are discussed with regard to different predation types (generalists vs. specialists) and the possible consequences of mixed release for biological control of spider mites in greenhouses.     

Oviposition Behavior of Interacting Predatory Mites: Response to the Presence of Con- and Heterospecific Eggs

Oviposition behavior may be affected by the presence of potential future competitors, mates, or predators of offspring. We examined patch choice, oviposition site preference and egg production in the predaceous mites Phytoseiulus persimilis and Neoseiulus californicus (Acari: Phytoseiidae) when given a choice between paired spider mite patches with and without conspecific eggs, with and without heterospecific eggs, and with conspecific or heterospecific eggs. Neoseiulus californicus females had no patch preference and distributed their eggs randomly in all choice situations. This was also the case with P. persimilis females given a choice between patches with and without conspecific eggs and between patches with either con- or heterospecific eggs. Phytoseiulus persimilis females confronted with patches with and without heterospecific eggs preferentially stayed and oviposited in the predator free patches. We discuss the oviposition strategies of P. persimilis and N. californicus with respect to food competition, cannibalism and intraguild predation.     

Cannibalism and interspecific predation in the phytoseiid mites Phytoseiulus persimilis and Neoseiulus californicus: predation rates and effects on reproduction and juvenile development

We examined intra- and interspecific predation of adult females and immature stages of the generalist Neoseiulus californicus and the specialist Phytoseiulus persimilis. Adult females and immatures of both predators exhibited higher predation rates on larvae than on eggs and protonymphs. N. californicus fed more inter- than intraspecifically. Predation on P. persimilis by N. californicus was more severe than vice versa. P. persimilis had higher predation rates on conspecifics than heterospecifics and was more prone to cannibalism than N. californicus. When provided with phytoseiid prey, P. persimilis suffered higher mortality than N. californicus. When held without food, adult females and protonymphs of N. californicus survived longer than the corresponding stages of P. persimilis. N. californicus females were able to sustain oviposition when preying upon P. persimilis, whereas cannibalizing females did not lay eggs. Females of P. persimilis were not able to sustain oviposition, irrespective of con- or heterospecific prey. Immatures of both predators were able to reach adulthood when provided with either con- or heterospecifics. Juvenile development of N. californicus was shorter with heterospecific vs. conspecific larvae; mortality of P. persimilis immatures was less when feeding on conspecific vs. heterospecific larvae. Different behavioral pattern in intra- and interspecific predation are discussed in regard to their feeding types (generalist vs. specialist).     

Intra- and interspecific predation by adult female Metaseiulus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae) when provisioned with varying densities and ratios of Tetranychus urticae (Acari: Tetranychidae) and phytoseiid larvae

The phytoseiid mites Metaseiulus occidentalis (Nesbitt) and Typhlodromus pyri Schueten are used together and alone as biological control agents against tetranychid pest mites of apple. Their effectiveness as control agents may be impacted by intraguild predation. The effects of prey species and prey density on the rates of inter- and intraspecific predation and oviposition by these two predators were investigated through a series of experiments. Adult female predators were given prey as mixed populations of phytoseiid larvae and larvae of a more preferred species, the spider mite, Tetranychus urticae Koch, at different densities and ratios. Typhlodromus pyri, more of a generalist predator, showed higher rates of predation and cannibalism on phytoseiid immatures at most prey densities and ratios. Manly preference indices indicated that T. pyri switched to feed on phytoseiid larvae at higher prey levels and ratios of T. urticae than M. occidentalis. This greater ability to use phytoseiid larvae as prey may help stabilize T. pyri populations when more preferred prey is unavailable. This may, in part, explain the observed persistence of T. pyri populations when M. occidentalis populations were decreasing in orchard test plots.