A test of temporal and spatial density dependence in the parasitism rates of introduced parasitoids on host, the arrowhead scale (Unaspis yanonensis) in stable host–parasitoids system

Abstract: In 1980, two species of parasitoid wasps (Aphytis yanonensis DeBach et Rosen and Coccobius fulvus Compere et Annecke) were introduced to Japan from China as biological control agents to combat the arrowhead scale (Unaspis yanonensis Kuwana). These introductions represent one of the most successful projects in the history of biological control in Japan. To examine whether density dependent parasitism was inevitable for success of biological control, we tried to detect temporal and spatial density dependence in parasitism rates using time‐series data of scale density, as well as parasitism, over a 16‐year period. The work was conducted in a Satsuma mandarin orange (Citrus unshiu Marc.) orchard in which we previously demonstrated that the system appeared to have stabilized after a decline in scale density following the introduction of the parasitoids. Earlier work also indicated that C. fulvus contributes most to the reduction in, and the stability of, scale density. In this study, we examined: (1) the relationship, on a whole‐orchard basis, between scale density and the rates of parasitism by A. yanonensis, C. fulvus, and a combination of the two species; (2) whether parasitism was positively correlated to scale density on a single‐tree basis among generations and (3) whether spatial density dependence was detectable within generations on an individual‐tree basis. Parasitism by A. yanonensis was temporally density‐dependent on scale population density at the whole‐orchard level, while parasitism by C. fulvus was not. Parasitism by A. yanonensis or by C. fulvus was rarely positively correlated to scale density at the single‐tree level, and spatial density‐dependence was hardly detected at all at this level. Most analyses of combined parasitism rates were similar to rates of parasitism by C. fulvus alone. Contrary to conventional wisdom of biological control theory, this study demonstrates that density dependence is not necessarily detected, even in a system in which a natural enemy has long held pest density stable at low levels.     

Biological control by two exotic parasitoids: eight-year population dynamics and life tables of the arrowhead scale

To determine the process of regulation of Unaspis yanonensis (Kuwana) (Hemiptera: Diaspididae) by the two introduced parasitoids, Aphytis yanonensis DeBach et Rosen and Coccobius fulvus (Compere et Annecke) (Hymenoptera: Aphelinidae), the temporal changes in the population density of U. yanonensis as well as the parasitism rates were monitored for eight years before and after the release of the two parasitoids in a Satsuma mandarin orange (Citrus unshiu Marc. (Rutaceae)) orchard. From 2–4 years after the release, the parasitism rate by C. fulvus gradually increased, eventually reaching 70%, while that by A. yanonensis showed a weak increase, remaining under 12%. During this period, the host density decreased to about 1/100 of the initial density. After the drastic decrease, the host density remained under 1/60 of the level previous to the release for at least 2 years with the populations of both parasitoids persisting. To estimate the ability of the two parasitoids to regulate the populations of U. yanonensis, life tables of U. yanonensis under natural conditions and predator/parasitoid-exclusion (bagged) conditions were compared. It was demonstrated that C. fulvus and A. yanonensis impose about 70% mortality rate on the host at mature adult stages and about 30% on the host at immature adult stages. The results have strongly confirmed the high capability of the two parasitoids as biological control agents for U. yanonensis, which was suggested by earlier studies. However, contrary to those studies, the present study did not support the complementarity of the two parasitoids in regulating the host population, suggesting that the effectiveness of C. fulvus alone in regulating the host population at low levels.     

矢尖蚧发生动态及其寄生性天敌

柑桔矢尖蚧在福建闽北地区一年发生3代。以雌成虫和部分若虫及少数雄蛹越冬．一龄幼蚧盛期,第一代为4月中,下旬。第二代7月上．中旬,第三代9月中旬前后。二龄幼蚧盛期．第一代为5月上、中旬,第二代7月下旬,和第三代9月下旬．后期世代重叠．福建已知寄生蜂6种．其中一种为重寄生蜂,以矢尖蚧黄蚜小蜂为优势种．寄生生蜂自然寄生率最高达49.1%。     

Fertility schedules ofunaspis yanonensis (Hemiptera: Diaspididae) in relation to daily temperature

Fertility schedules of Unaspis yanonensis on citrus leaves were investigated from 1962 to 1971 for the first generation and from 1964 to 1971 for the second generation, at the Okitsu Branch of the Fruit Tree Research Station in Shizuoka Prefecture. The fertility curves were commonly characterized by a first major peak and a few subsequent minor peaks, although their shapes differed from year to year. Models estimating these fertility curves of each generation were constructed in relation to the fluctuations in average daily temperature, on the assumption that the curve was composed of two peaks, i.e., bimodal. Estimated curves were well fitted to observed ones.     

寄生柑桔矢尖蚧的跳小蜂一新种：膜翅目：跳小蜂科

本文记述盾蚧跳小蜂ＣｏｃｃｉｄｅｎｃｙｒｔｕｓＡｓｈｍｅａｄ１新种,即长尾 盾蚧跳小蜂     

A ten-year study of population dynamics of citrus pests in the pesticide-reduced orchard

To determine the effectiveness of a pest management system that uses pesticides at a low level, we censused populations of seven insect pests and three plant diseases from 1980 to 1989 in a citrus orchard which was managed with a pesticide-reduced and pesticide-free protocols, in Wakayama Prefecture, Japan. In the orchard, we controlled the pests solely by spraying petroleum oil once a year from 1980 to 1985, by not spraying insecticide in 1986, and spraying only germicide in 1987. The arrowhead scale population remained much lower level at which citrus trees begin to wither when petroleum oil was sprayed, whereas it rapidly increased and began to wither trees during the years without spraying petroleum oil. The Indian wax scale population rapidly increased only during a 2-year period and then declined. Although the infection level of the sooty mold was unusually high on the trees where the density of the scale was high, this pathogen did little damage to citrus trees. The population of the red wax scale gradually increased throughout the census period but did not reach the level at which citrus trees begin to be damaged. Other pests also caused negligible damages to citrus trees. The results indicated that the pesticide-reduced pest management system which was proposed by Inoue and Ohgushi (1976, 1977) is valid for the prevention of the outbreak of the arrowhead scale, and that is has the sufficient control efficiency for the other pests in citrus orchards.     

Brood sex ratios of the solitary parasitoid wasp, Coccophagus atratus

Abstract.

• 1 Female eggs of Coccophagus atratus are deposited within the haemolymph of coccoid scale insects. Male eggs are deposited on to late larval and prepupal stages of parasitoids of scale insects, including conspecifics.
• 2 When presented with either one host type or a combination of both host types, female C.atratus deposit all their available eggs, assigning the appropriate sex egg to each host encountered. Brood sizes are not adjusted for different combinations of hosts.
• 3 Behavioural observations show that females do not move away from patches of hosts until all their eggs are laid, regardless of the host type.
• 4 Brood sex ratios varied with changes in the relative availability of hosts for males and hosts for females. When both host-types were present in equal numbers, male biased sex ratios resulted (mean ±SEM =0.71 ± 0.009) and when 70% of hosts provided were suitable for female eggs, mostly female-biased sex ratios resulted (mean ± SEM = 0.37±0.01).
• 5 Our results do not fit predictions based on the assumption that a sex ratio of 0.5 should be expected in C.atratus. Observed sex ratios indicate that the unusual life histories of these parasitoids need to be taken into account in explanations of their sex ratios.

     

20种杀虫剂对柑橘矢尖蚧的室内毒力测定

柑橘矢尖蚧Unaspis yanonensis(Kuwana)是危害柑橘的重要害虫之一。为了筛选高毒有机磷农药的替代物,在室内条件下采用浸渍法分别测定20种杀虫剂原药对柑橘矢尖蚧1龄若虫的毒力。结果表明:供试杀虫剂对柑橘矢尖蚧的毒力大小依次为:甲氨基阿维菌素苯甲酸盐>阿维菌素>硝虫硫磷>噻嗪酮>杀扑磷>吡虫啉>乙酰甲胺磷>毒死蜱>喹硫磷>亚胺硫磷>稻丰散>敌百虫>残杀威>氟氯氰菊酯>甲氰菊酯>甲氧虫酰肼>苯氧威>高效氯氰菊酯>石硫合剂>矿物油。     

Effect of oil emulsion sprays on parasitoids of the black parlatoria, Parlatoria ziziphi, in grapefruit

The black parlatoria, Parlatoria ziziphi, a common pest of citrus in the tropics and subtropics, has become the most important citrus pest in Upper Egypt. Spray oils may be a relatively safe alternative to harmful synthetic insecticides. However, the effect of spray oils on black parlatoria and associated parasitoids is unknown. Field studies were conducted in Giza, Egypt to assess the effect of two experimental spray oils on P. ziziphi and three associated parasitoid species on grapefruit (Citrus paradisi). Triona oil was more effective than Shecrona oil and reduced scale populations by up to 99% 75 days after application. The parasitoid Encarsia citrina was not affected significantly by either spray oil. Triona oil was slightly harmful to the other primary parasitoid, Habrolepis aspidioti and reduced parasitism rate by Marietta leopardina. However, because the latter species is a hyperparasitoid, the reduction in its number by Triona was beneficial. Triona application is therefore highly effective in controlling the black parlatoria and it reduced the rate of hyperparasitism by M. leopardina. The oils had only a minor negative impact and only on the less important primary parasitoid in the system.     

柑桔矢尖蚧生态学研究

1 996～ 1 999年 ,在浙江东南沿海自然变温下对矢尖蚧的发生历期与日平均气温的相关性、各虫态的发育起点温度和有效积温以及生命表等进行了系统的研究。第 1、2、3代雌性寿命分别为 1 0 9.5、1 1 6.2 (一年发生 2代的个体为2 5 6.5 d)和 2 60 .0 d左右 ;完成 1代所需历期分别为 70 .1± 3 .9、67.5± 9.8和 2 1 1 .4± 1 6.5 d。各虫态发生历期与日平均气温明显呈负相关。雌一龄、二龄、产卵前期和雄一龄、二龄、蛹 (包括预蛹 )的发育起点温度分别为 1 1 .5、9.6、8.7、1 4.7、1 3 .6和 1 3 .7℃ ,有效积温分别为 2 61 .8、2 83 .8、5 3 0 .4、1 65 .9、2 0 6.2和 94.0日度。第 1、2、3代每头雌成虫的产卵量分别为 93 .0± 42 .7、1 3 4.2± 65 .6和 1 96.3± 81 .9粒。第 2、3代存在世代重叠现象。第 1、2、3代的种群趋势指数避雨区分别为 2 2 .5 6、3 1 .1 7和 2 .48,露地区分别为 2 1 .0 9、2 9.76和 1 .96,表明在新区的种群自然增长能力很强。研究还揭示了在新区对矢尖蚧种群数量起控制作用的主要因子是自然死亡和失踪 ,因而必需从老发区引进、饲养释放和保护有效的寄生蜂等天敌。     

Population dynamics of Siphoninus philyreae in California in the presence and absence of a parasitoid, Encarsia partenopea

Abstract. 1. Densities of the whitefly, Siphoninus phillyreae Haliday, remained at low levels at two sites where a parasitoid, Encarsia parknopea (Walker), was released on whitefly-infested ash, Fraxinus sp., and pomegranate, Punica granatum. Populations of S.phillyreae at control sites, where parasitoids were absent, were increasing in density at the beginning of the summer.
2. By mid-summer, E.partenopea had appeared at all four control sites, and densities of S.phillyreae declined to levels similar to those at the release sites.
3. In the absence of the parasitoid, the age structure of S.phillyreae populations was dominated by the egg stage, indicating a population increasing in density. After E.partenopea became abundant at a site, the age structure of the population had a decreasing proportion of young stages.
4. The changes in S.phillyreae age structures were explained by examining the percentage of fourth instar S.phillyreae from which E.partenopea , as opposed to adult whiteflies, emerged. After the parasitoid became abundant at a site, the majority of fourth instars produced parasitoids rather than whitefly adults. The result was that the adult S.phillyreae population declined, and few eggs were laid.
5. The dynamics of the interaction between E.partenopea and S.phillyreae were similar on ash and pomegranate.     

中国新栎盾蚧属一新种及二新纪录种(同翅目:蚧总科:盾蚧科)

记述新栎盾蚧属Neoquernaspis Howell et Takagi,1981一新种,即细管新栎盾蚧N.leptosipha sp.nov和2种中国分布新纪录种,即石柯新栎盾蚧N.beshearae Liu et Tippins,1988和尼泊尔新栎盾蚧N.nepalensis (Takagi,1977),并编制了该属中国已知种类检索表,新种模式标本和新纪录标本保存于西北农业大学昆虫博物馆。     

Host population structure affects field sex ratios of the heteronomous hyperparasitoid, Coccophagus atratus

Abstract.

• 1 Second instar Filippia gemina de Lotto scale insects are the preferred hosts of female Coccophugus atrutus Compere larvae. These scale insects were found on their host plants, Chrysanthemoides monilifera Norlindh and Cliffortia strobilifera Mettenius, only at certain times during a 1 year sampling programme.
• 2 Late larval instars and prepupae of C.atratus, and a Metaphycus species, are the preferred hosts of male C.atratus larvae. These hosts, although they occurred on the same host plants as hosts for female C.atratus, were most numerous at different times during the sampling period.
• 3 The ratio of hosts suitable for C.atratus varied from a predominance of hosts suitable for females through to a predominance of hosts suitable for males. Sex ratios of adult C.atratus followed a similar trend but did not reflect, exactly, the ratio of available hosts. Differences in mortality between sexes and hyperparasitism may account for this anomaly.
• 4 Variable population sex ratios observed in C.atratus apparently result from the behaviour of individual females in which brood sex ratios are dependent on the relative availability of hosts for males and hosts for females. This behaviour, in turn, may result from variability in the host population structure but may also result from selection pressures operating at the time that heteronomous hyperparasitism evolved.