斑翅肩花蝽生物学特性、生境及食性选择

斑翅肩花蝽Tetraphleps galchanoides Ghauri是铁杉球蚜Adelges tsugae Annand (hemlock woolly adelgid) 的重要天敌昆虫。在云南省兰坪县天生桥林区通过实验室和林间的饲养观察与测定、林间线路调查等方法, 研究了斑翅肩花蝽的生物学特性、生境及食性选择,并描述各虫态形态特征。斑翅肩花蝽在该林区一年发生2代, 无世代重叠, 寿命长。第1代（5月下旬至10月下旬）卵期13.8±1.6 d,若虫期97.6±7.4 d,成虫期55.2±4.7 d;第2代（11月中旬至翌年4月下旬）卵期11.3±1.1 d,若虫期105.7±8.5 d,成虫期60.4±5.3 d。若虫共5龄,以5龄若虫在云南铁杉Tsuga dumosa枝条树皮裂缝下或枯枝落叶层内越冬。雌雄成虫性比8.5∶1,雌雄成虫飞行缓慢,其飞行活动主要受到交尾、产卵、捕食铁杉球蚜补充营养的影响,多在树冠下层活动。该林区的斑翅肩花蝽最适生境选择： 海拔为2 851~2 980 m,云南铁杉密度为13.3~15.5株/100 m、郁闭度为0.61~0.70。以寄主铁杉球蚜及附近常见的冷杉球蚜Aphrastasia pectinatae (Cholodkovsky)、华山松球蚜Pineus armandicola Zhang和落叶松球蚜Adelges laricis Vall为食物进行选择性试验,结果表明,斑翅肩花蝽对这4种球蚜的选择性存在显著差异,最喜好捕食铁杉球蚜,可成为生物防治铁杉球蚜的主要天敌之一。     

斑翅肩花蝽布丁人工饲料的饲养效果评价

斑翅肩花蝽 Tetraphleps galchanoides Ghauri是铁杉球蚜 Adelges tsugae (Annand) (hemlock woolly adelgid)的重要天敌。为开展斑翅肩花蝽的人工繁殖, 我们自主研制了一种主要成分为蛋白质、 脂肪、 碳水化合物的原料配制布丁人工饲料, 所配制人工饲料产率为74.5%, 含水率为8.6%, 感官评定得分为81.7分。为评价斑翅肩花蝽布丁人工饲料的饲养效果, 在实验室以铁杉球蚜作对照, 用布丁人工饲料饲养斑翅肩花蝽, 测定了斑翅肩花蝽若虫发育历期、 存活率及成虫繁殖力, 并调查了若虫和成虫林间捕食量。结果表明： 用布丁人工饲料饲养的斑翅肩花蝽若虫发育历期（103.2±6.5 d）与对照的若虫发育历期（105.7±8.4 d）不存在显著差异（P>0.05）; 用布丁人工饲料饲养的斑翅肩花蝽若虫存活率（73.2%）略低于对照的若虫存活率（77.4%）, 而且第1, 2和3代成虫获得率相近; 取食布丁人工饲料的斑翅肩花蝽成虫, 在产卵前期、 产卵期、 产卵量与对照组均无显著差异, 但孵化率、 成虫寿命存在显著差异, 取食布丁人工饲料的卵孵化率为85.8%, 成虫寿命为51.9±4.0 d, 而对照组的卵孵化率仅为71.4%, 成虫寿命仅为37.4±2.6 d。林间释放用布丁人工饲料饲养的斑翅肩花蝽, 若虫和成虫均有效捕食铁杉球蚜。因此, 此种布丁人工饲料可用于大量饲养繁殖斑翅肩花蝽, 满足大面积生物防治铁杉球蚜的需要。     

不同猎物饲喂对南方小花蝽捕食量和喜好性的影响

为探讨南方小花蝽对不同猎物的捕食喜好性,室内用西花蓟马、蚕豆蚜、二斑叶螨、混合饲料(同时饲喂3种猎物)分别饲喂南方小花蝽驯化两代,研究了4种饲喂处理的南方小花蝽初孵若虫、5龄若虫和雌成虫对西花蓟马、蚕豆蚜和二斑叶螨的捕食量和喜好性。结果显示不同猎物饲喂处理驯化的南方小花蝽1龄若虫对同一种猎物的捕食量和喜好性均不存在显著差异。南方小花蝽5龄若虫和雌成虫对某种猎物的捕食量因前期取食的猎物种类不同而有显著差异。南方小花蝽5龄若虫和雌成虫均表现出对西花蓟马2龄若虫的正喜好性。蚕豆蚜饲喂处理的5龄若虫和雌成虫对蚕豆蚜表现出正喜好性,除二斑叶螨饲喂处理外其余3种处理的南方小花蝽5龄若虫和雌成虫均表现出对二斑叶螨的负喜好性。以上结果表明4种饲喂驯化处理的南方小花蝽1龄若虫的喜好性不受前期取食猎物的影响,但5龄若虫和雌成虫对前期取食过的猎物的喜好性增强,存在一定的学习行为。     

东亚小花蝽对西方花蓟马和二斑叶螨的捕食选择性

多食性天敌对猎物的捕食选择性及猎物密度对天敌捕食的干扰作用直接影响到天敌对不同猎物的控制作用.在实验室条件下研究了东亚小花蝽对西方花蓟马和/或二斑叶螨不同虫态的捕食选择性,以及两猎物中一种猎物的密度变化对小花蝽取食另一种猎物的影响.结果如下:东亚小花蝽5龄若虫和成虫对西方花蓟马2龄若虫的捕食选择性均强于对其成虫,对二斑叶螨的选择性为雌成螨>若螨>幼螨.实验中西方花蓟马2龄若虫是东亚小花蝽最喜好的虫态.二斑叶螨雌成螨密度固定为60头/19.63cm2,西方花蓟马若虫密度从10增加到60时显著地减少了东亚小花蝽对二斑叶螨的取食.反之,固定西方花蓟马同样密度,增加二斑叶螨密度却没有显著改变小花蝽对西方花蓟马的取食.此结果进一步表明,西方花蓟马是东亚小花蝽更喜好的猎物.     

黑肩绿盲蝽捕食褐飞虱卵的功能与数值反应

褐飞虱作为水稻的重要迁飞性害虫,至今未见有效的生物防治技术报道。黑肩绿盲蝽对褐飞虱卵及低龄若虫有较强的捕食能力,为评价黑肩绿盲蝽对褐飞虱的控害能力,研究了黑肩绿盲蝽若虫各虫期和雌雄成虫对褐飞虱卵的捕食功能反应与数值反应。功能反应研究结果表明,黑肩绿盲蝽对褐飞虱卵的捕食功能反应符合HollingⅡ型方程,捕食量在一定范围内随着猎物密度的增加而增加,若虫的捕食能力大于成虫;四龄若虫理论捕食量最大,为104.2粒卵/d。数值反应研究结果表明,不同褐飞虱卵密度对黑肩绿盲蝽的生长、发育、繁殖有着显著影响。随着猎物密度增大,黑肩绿盲蝽若虫发育速率、雌虫产卵量、孵化率及雌性比增大,成虫寿命减小,最后趋于稳定。猎物密度1、3、5卵/d分别是黑肩绿盲蝽若虫存活、成虫羽化及维持种群最低繁殖力的临界值。在天敌控害潜能的研究过程中,数值反应的研究目的在于探讨捕食者对猎物密度的依赖程度,探明能引起捕食者种群衰退的猎物密度临界值,为大田释放捕食者时增补替代寄主,增强捕食者持续控害能力提供理论依据。     

微小花蝽对四种猎物的喜好性

【目的】了解微小花蝽Orius minutus(Linnaeus)对4种主要自然猎物的喜好性。【方法】通过非选择性和选择性试验,室内测定并比较了微小花蝽初孵若虫、刚蜕皮后的5龄若虫和新羽化雌成虫对朱砂叶螨Tetranychus cinnabarinus(Boisduval)成螨、桃蚜Myzus persicae(Sulzer)低龄若虫、西花蓟马Frankliniella occidentalis(Pergande)2龄若虫和烟粉虱Bemisia tabaci(Gennadius)2-3龄若虫的日捕食量和喜好性Ci值。【结果】非选择性试验结果表明,在4种供试猎物中,微小花蝽初孵若虫对西花蓟马2龄若虫和朱砂叶螨成螨的日捕食量为最大,分别为14.20头/d和12.40头/d,刚蜕皮后的5龄若虫和新羽化雌成虫对朱砂叶螨成螨的日捕食量均为最大,分别为44.40头/d和37.20头/d。选择性试验结果表明,微小花蝽初孵若虫对西花蓟马2龄若虫和朱砂叶螨成螨均表现为正喜好性,其喜好性Ci值无显著差异,刚蜕皮后的5龄若虫和新羽化雌成虫对西花蓟马2龄若虫和桃蚜低龄若虫均表现为正喜好性,2者对西花蓟马的喜好性Ci值均显著大于对桃蚜。【结论】微小花蝽日捕食量最大的猎物是朱砂叶螨,其次是西花蓟马,而其最喜好的猎物则是西花蓟马。     

微小花蝽对小菜蛾捕食控制的能力

为了明确微小花蝽以小菜蛾卵做为饲料的适宜性及其对小菜蛾的控制能力,在室内以桃蚜作为参比猎物,研究捕食小菜蛾卵对微小花蝽生长发育、繁殖的影响,并结合捕食功能反应评价微小花蝽对小菜蛾的捕食能力.结果表明: 微小花蝽取食小菜蛾卵能够完成世代发育,并能够正常繁育后代.取食小菜蛾卵时,微小花蝽雌、雄若虫的历期(♀: 12.3 d,♂: 12.2 d)、成虫体长[♀: (2.13±0.01) mm,♂: (1.91±0.00) mm]、体宽[♀: (0.87±0.01) mm,♂: (0.71±0.01) mm]、单雌产卵量(12.7±1.1)、产卵前期[(5.1±0.6) d]和产卵期[(3.7±0.4) d]均与桃蚜处理组无显著差异;雌、雄成虫寿命[♀: (10.7±1.4) d,♂: (9.1±1.3) d]显著长于桃蚜处理组[♀: (8.5±0.5) d,♂: (6.4±0.3) d];若虫存活率[(65.0±6.8)%]不及桃蚜处理组[(80.0±8.2)%],且雌性比例偏低.微小花蝽对小菜蛾的捕食功能反应符合HollingⅡ型方程.微小花蝽1～5龄若虫对小菜蛾卵的日均最大捕食量(N_max)分别为7.5、16.3、23.3、29.1和38.7粒;雌、雄成虫的日均最大捕食量分别为39.0和26.9粒;5龄若虫对小菜蛾低龄幼虫的日均最大捕食量为41.3头;雌、雄成虫的日均最大捕食量分别为40.8和23.9头.单头雌、雄微小花蝽一生中最多可捕食小菜蛾卵(711.3±58.1)和(535.4±30.6)粒,小菜蛾低龄幼虫(371.9±52.0)和(253.9±32.3)头.微小花蝽以小菜蛾卵饲养可行,且对小菜蛾具有良好的控制作用.     

南方小花蝽对西花蓟马和蚕豆蚜的捕食作用

南方小花蝽Orius similis是多种小型害虫的重要天敌昆虫,为了掌握其控制潜能,本文研究了南方小花蝽对西花蓟马Frankliniella occidentalis和蚕豆蚜Aphis craccivora的捕食作用。研究结果表明南方小花蝽3～5龄若虫和雌成虫对西花蓟马和蚕豆蚜的功能反应均符合HollingⅡ型方程,南方小花蝽3～5龄若虫和雌成虫对西花蓟马2龄若虫的瞬时攻击率均高于蚕豆蚜。南方小花蝽5龄若虫对蚕豆蚜的控制能力比雌成虫强,而对西花蓟马的控制能力比雌成虫差。南方小花蝽5龄若虫对西花蓟马2龄若虫和蚕豆蚜的捕食率（E）随着捕食者自身的密度（P）的增加而下降,其干扰反应方程分别为E=0.412P-1.623和E=0.416P-1.639。南方小花蝽5龄若虫对西花蓟马2龄若虫和蚕豆蚜有明显的选择性,5龄若虫喜欢取食西花蓟马2龄若虫,但前期取食的猎物对其选择性有明显的影响,更喜欢选择前期取食过的猎物。     

南方小花蝽对不同猎物捕食作用及利用效率

室内用棉蚜,花蓟马及棉花花粉饲养南方小花蝽,通过对南方小花蝽捕食两种猎物及取食棉花花粉后的体重的增长以及同时段内对棉蚜,花蓟马及棉花花粉减少的量的测定,得到南方小花蝽取食不同食物后的生长速率及其对食物的利用效率,同时还研究了南方小花蝽成虫和若虫对混合猎物（棉蚜,棉铃虫卵,红铃虫卵）中各猎物的捕食作用及其在多猎物（红铃虫卵,棉叶螨成螨,花蓟马若虫）不同密度水平下的捕食效应。结果表明,棉蚜与花蓟马可以较好地满足南方小花蝽正常生长发育所需的营养,南方小花蝽对两种猎物的利用效率显著高于棉花花粉,在混合猎物中南方小花蝽成虫和若虫均嗜食棉蚜,其次为红铃虫卵和棉铃虫卵;对于同一种猎物,南方小花蝽成虫和若虫在高密度下的日平均捕食量均显著高于低猎物密度下的日平均捕食量,而对于同一密度的不同猎物,南方小花蝽在低猎物密度时对供试的3种猎物无明显的选择性,在中,高密度时对供试的3种猎物则表现出明显的嗜食性差异。其嗜好程度依次为红铃虫卵,花蓟马若虫,棉叶螨成螨,通过研究有助于更好地了解与掌握南方小花蝽对不同食物的需求及其在田间的食物转换规律,从而更好地进行南方小花蝽的室内人工大量饲养,使南方小花蝽更好地成为棉田害虫种群综合治理中的重要组成部分并发挥其应有的作用。     

人工饲料饲养的叉角厉蝽对昆虫的捕食能力评价

叉角厉蝽Eocanthecona furcellate(Wolff)是广泛分布于热带亚热带地区的一种重要捕食性天敌昆虫。为评估人工饲料饲养的叉角厉蝽的捕食能力,在实验室采用捕食功能反应的方法,以黄粉虫作为中介猎物饲养的叉角厉蝽为对照,评价了人工饲料饲养的叉角厉蝽3龄若虫、5龄若虫以及雌成虫对黄粉虫Tenebriomolitor(L.)幼虫及斜纹夜蛾Spodoptera litura(Fabricius)3龄幼虫、5龄幼虫的捕食效能。结果表明,两种饲料饲养的不同虫态叉角厉蝽的捕食量均随着猎物密度的增加而上升,当猎物密度增加到一定水平,捕食量趋于稳定,其捕食功能反应均符合HollingII模型。人工饲料组饲养的各虫态叉角厉蝽与对照组的对黄粉虫幼虫的捕食量没有明显差异;在饱和猎物密度条件下,人工饲料饲养的叉角厉蝽3龄若虫、5龄若虫以及雌成虫对斜纹夜蛾3龄幼虫的日最大捕食量分别为7.20、9.20、14.60头,对斜纹夜蛾5龄幼虫的日最大捕食量分别4.20、5.80、6.20头,均略低于对照组,但从取食猎物数量上来看,仍保持较强的捕食能力。     

Comparison of numerical response and predation effects of two coccinellid species on hemlock woolly adelgid (Homoptera: Adelgidae)

The hemlock woolly adelgid, Adelges tsugae Annand, is an introduced pest in North America that is native to Asia, and is causing extensive damage to eastern hemlock (Tsuga canadensis Carriere) and Carolina hemlock (Tsuga caroliniana Englemann) in the eastern United States. We compared two coccinellids imported for biological control of the adelgid: Scymnus ningshanensis Yu et Yao from China and Pseudoscymnus tsugae Sasaji and McClure from Japan. In a laboratory study, we measured the numerical response of each beetle species to a range of prey densities, and in field studies we examined the reproductive success and ability of the coccinellids to reduce populations of the hemlock woolly adelgid. In the laboratory, S. ningshanensis showed a positive numerical response as hemlock woolly adelgid density increased, and P. tsugae showed a density-independent response. In field cages, the presence of S. ningshanensis resulted in negative hemlock woolly adelgid population growth, in contrast to positive growth in both control cages and cages containing P. tsugae. Both our laboratory and field experiments suggest that S. ningshanensis has good potential as a biological control agent of hemlock woolly adelgid.     

Orientation behavior of the predator Laricobius nigrinus (Coleoptera: Derodontidae) to hemlock woolly adelgid and host tree odors in a multi-chambered olfactometer

We studied the adult ambulatory response of the predator, Laricobius nigrinus Fender (Coleoptera: Derodontidae), to odors from its prey, Adelges tsugae Annand, the hemlock woolly adelgid, and foliage of hemlock woolly adelgid, host hemlocks (Tsuga spp.), and other conifers. Both the predator and hemlock woolly adelgid are apparently native to western North America, but the predator is being released in the eastern United States, which has different hemlock species, for biological control of a lineage of hemlock woolly adelgid inadvertently introduced from Japan. L. nigrinus responded to odors from hemlock woolly adelgid host trees, but not to odors from hemlock woolly adelgid. L. nigrinus collected from hemlock woolly adelgid-infested western hemlock were more strongly attracted to odors from western hemlock [Tsuga heterophylla (Rafinesque) Sargent] than eastern hemlock [Tsuga canadensis (L.) Carrière] in most trials. Odors from western white pine (Pinus monticola Douglas ex D. Don) and white spruce [Picea glauca (Moench) Voss] were as attractive as western hemlock odors whereas odors from Douglas-fir [Pseudotsuga menziesii variety menziesii (Mirbel)] and ponderosa pine (Pinus ponderosa Douglas ex Lawson) were avoided. L. nigrinus reared on hemlock woolly adelgid-infested eastern hemlock in the laboratory were lethargic and were not attracted to either eastern or western hemlock odors. Predators collected in the field and tested monthly from December to March responded similarly each month, except February, when they flew rather than walked in the olfactometer, suggesting a period of dispersal or mate finding at that time of year. The implications of these results for programs to release L. nigrinus in the eastern United States for control of hemlock woolly adelgid are discussed.     

Web orientation and prey resources for web-building spiders in eastern hemlock

We examined the arthropod community on eastern hemlock, Tsuga canadensis (L.) Carr, in the context of its role in providing potential prey items for hemlock-associated web-weaving spiders. Using sticky traps simulating spider webs, we evaluated what prey items are available to web-weaving spiders in eastern hemlock based on web orientation (horizontal versus vertical) and cardinal direction. We found that the overwhelming majority (>70%) of prey items available to spiders in hemlock canopies were Diptera. Psocoptera, Hymenoptera, and Hemiptera comprised most of the remaining potential prey. A significant direction × orientation interaction, and greater trap capture in some direction-orientation combinations, suggests that spiders might locate their webs in eastern hemlock canopies for thermoregulatory purposes, ultimately optimizing prey capture. We also evaluated these findings in the context of hemlock infestation by the invasive hemlock woolly adelgid, Adelges tsugae Annand. The adelgid is a sedentary insect with a mobile crawler stage that provides a readily available, easily obtained food source for predators in hemlock canopies. However, an abundance of alternative prey will affect within canopy spider distribution and the potential intensity with which spiders consume these prey. Understanding the response of spiders to potential prey availability is essential to understanding the trophic interactions involving these predators and their potential for influencing herbivore populations.     

Feeding preference of three lady beetle predators of the hemlock woolly adelgid (Homoptera: Adelgidae)

In a laboratory study, we tested the feeding preferences of three coccinellid predators of hemlock woolly adelgid, Adelges tsugae Annand, an introduced pest of hemlock in the eastern United States. The species tested were Sasajiscymnus tsugae Sasaji & McClure (formerly Pseudoscymnus tsugae) from Japan, Scymnus ningshanensis Yu & Yao from China, and Harmonia axyridis (Pallas), a generalist species introduced from Asia that is currently widespread in eastern hemlock, Tsuga canadensis Carriere, forests. We measured the feeding preference of each beetle species when given the choice of A. tsugae and either 1) Pineus strobi (Hartig) on Pinus strobus L.; 2) Adelges laricis Vallot on Larix decidua Mill.; 3) Adelges cooleyi (Gillette) on Pseudotsuga menziesii (Mirb.) Franco; or 3) Paraprociphilus tessellatus (Fitch) on Alnus serrulata (Ait.) Willd. We evaluated beetle preference for adults, nymphs, and eggs of each prey species. Generally, when adult or nymphal prey stages were compared, S. tsugae preferred A. tsugae adults to P. strobi, A. cooleyi, A. laricis, and P. tessellatus. S. ningshanensis showed less preference between adelgid species, but it did not prefer P. tessellatus nymphs. When preferences for adelgid eggs were assayed, S. tsugae and S. ningshanensis showed no preference between A. tsugae and A. cooleyi or P. strobi, but S. tsugae did prefer A. tsugae to A. laricis. Larvae of S. tsugae were unable to survive on P. tessellatus nymphs. H. axyridis adults readily consumed both A. tsugae and P. tessellatus, but H. axyridis larvae did not complete their life cycle on A. tsugae. Our host range tests suggest that S. ningshanensis and S. tsugae may feed on several species of Adelgidae and that A. tsugae is often preferred.     

Factors affecting settlement rate of the hemlock woolly adelgid,Adelges tsugae,on eastern hemlock,Tsuga canadensis

1 We assessed the importance of several factors potentially affecting the settlement rate of the invasive hemlock woolly adelgid Adelges tsugae (Hemiptera: Adelgidae) on uninfested foliage of the eastern hemlock, Tsuga canadensis. We conducted our experiments in Massachusetts (U.S.A.) with overwintering sistens adelgids, and applied standard densities of infested foliage to uninfested branches in a planned multiple‐comparison design. 2 Settlement rates of progrediens crawlers produced by the overwintering sistens were highest when adelgid‐infested foliage was loosely attached to uninfested foliage and both branches were then enclosed in a mesh sleeve. 3 Early‐emerging crawlers settled at a higher rate than did late‐emerging crawlers. 4 Increasing the density of infested branches did not affect settlement rates. 5 We also tested whether less severe winter conditions improved settlement, and found that overwintering infested foliage in a refrigerator decreased settlement rate relative to foliage overwintered outdoors. 6 Our results suggest a protocol for adelgid inoculations that could substantially increase the success rate of experimental manipulations and encourage additional research on the population dynamics of this pest.     

Range expansion and population dynamics of co-occurring invasive herbivores

Although a range of studies have suggested that competition plays a critical role in determining herbivore assemblages, there has been little work addressing the nature of interactions between competing invasive herbivores. We report the results of research on the hemlock woolly adelgid Adelges tsugae (‘HWA’) and elongate hemlock scale Fiorinia externa (‘EHS’), invasive herbivores that both feed on eastern hemlock (Tsuga canadensis). HWA has been linked to hemlock mortality throughout the East Coast of the US; the loss of hemlock threatens to permanently alter surrounding ecosystems. We assessed the spread and impact of both species by resurveying 142 hemlock stands across a 7,500 km² latitudinal transect, running from coastal CT to northern MA, for HWA and EHS density as well as hemlock mortality. These stands had been previously surveyed in either 1997–1998 (CT) or 2002–2004 (MA). While the number of HWA-infested stands has increased, per-stand HWA density has substantially decreased. In contrast, EHS distribution and density has increased dramatically since 1997–1998. Hemlock mortality was much more strongly related to HWA density than to EHS density, and many stands remain relatively healthy despite an overall increase in hemlock mortality. There was a positive correlation between HWA and EHS densities in stands with low mean HWA densities, suggesting the potential for host-plant-mediated facilitation of EHS by HWA. Our findings underline the importance of research explicitly addressing interactions between competing invasive species, and of determining the potential consequences of these interactions for the invaded ecosystem.     

Reshaping the Ecology of Invading Populations of Hemlock Woolly Adelgid, Adelges tsugae (Homoptera: Adelgidae), in Eastern North America

Hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae), is native to Japan where it is an innocuous inhabitant of Tsuga diversifolia Masters and T. sieboldii Carriere throughout their natural growing areas. Native adelgid populations are regulated by host resistance and natural enemies, in particular the oribatid mite, Diapterobates humeralis (Hermann) and the coccinellid beetle, Pseudoscymnus tsugae Sasaji and McClure. Invading populations of A. tsugae in western North America on T. heterophylla Sargent and T. mertensiana Carriere are mainly regulated by host resistance. However, invading populations in eastern North America attain damaging levels on T. canadensis (L.) Carriere and T. caroliniana Engelmann and are regulated mainly by weather and negative density-dependent feedback mechanisms related to host deterioration. Although A. tsugae is only passively dispersed by wind, birds, forest-dwelling mammals and humans, it is spreading at an alarming rate and is sufficiently cold hardy to threaten the existence of the two eastern hemlock species throughout their natural ranges. The current hope for suppressing invading populations of hemlock woolly adelgid in eastern North America lies with the exotic predator, P. tsugae. Extensive laboratory studies of the biology and predatory ability of P. tsugae revealed that it feeds on all life stages of its prey, that its multivoltine life cycle is well synchronized with that of the adelgid, and that it has great potential for biological control. We have reared and released nearly 130,000 adults of P. tsugae in forests in Connecticut, New Jersey and Virginia during the past four years. P. tsugae has reproduced, dispersed, overwintered and reduced densities of hemlock woolly adelgid by 47–88% in only five months on release branches at these sites. Current studies are investigating the long-term ability of P. tsugae to regulate invading populations of A. tsugae in eastern North America.     

Facilitation between invasive herbivores: hemlock woolly adelgid increases gypsy moth preference for and performance on eastern hemlock

1. Interactions between invertebrate herbivores with different feeding modes are common on long-lived woody plants. In cases where one herbivore facilitates the success of another, the consequences for their shared host plant may be severe. Eastern hemlock (Tsuga canadensis), a canopy-dominant conifer native to the eastern U.S., is currently threatened with extirpation by the invasive stylet-feeding hemlock woolly adelgid (Adelges tsugae). The effect of adelgid on invasive hemlock-feeding folivores remains unknown. 2. This study evaluated the impact of feeding by hemlock woolly adelgid on gypsy moth (Lymantria dispar) larval preference for, and performance on, eastern hemlock. To assess preference, 245 field-grown hemlocks were surveyed for gypsy moth herbivory damage and laboratory paired-choice bioassays were conducted. To assess performance, gypsy moth larvae were reared to pupation on adelgid-infested or uninfested hemlock foliage, and pupal weight, proportional weight gain, and larval period were analysed. 3. Adelgid-infested hemlocks experienced more gypsy moth herbivory than did uninfested control trees, and laboratory tests confirmed that gypsy moth larvae preferentially feed on adelgid-infested hemlock foliage. Gypsy moth larvae reared to pupation on adelgid-infested foliage gained more weight than larvae reared on uninfested control foliage. 4. These results suggest that the synergistic effect of adelgid and gypsy moth poses an additional threat to eastern hemlock that may increase extirpation risk and ecological impact throughout most of its range.