Host discrimination in the parasitoid Ooencyrtus nezarae: the role of the egg stalk as an external marker

Laboratory experiments were conducted to examine the role of the egg stalk in host discrimination by Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), an egg parasitoid of the bean bug, Riptortus clavatus Thunberg (Hemiptera: Alydidae). These experiments showed that females that have oviposited in unparasitized hosts within 1 h before the test discriminated between parasitized and unparasitized hosts. When protruding parts of the parasitoid's egg stalks were removed from hosts, the latter were accepted by experienced females. This suggests that the protruding portion of the parasitoid egg stalk functions as an external marker. This part of the egg stalk was responsible for host discrimination up to 8 days after parasitism. Internal discrimination was also observed on hosts 3 or 8 days after parasitism.

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Résumé Des expériences de laboratoire ont permis d'examiner l'influence du pédoncule de l'oeuf dans la sélection des hôtes par O. nezarae Ishii (Hym.: Encyrtidae), parasite d'oeufs de Riptortus clavatus Thunberg (Hemip.: Alydidae). Les femelles qui avaient pondu dans un hôte vierge dans l'heure qui avait précédé l'expérience ont été capables de choisir entre des hôtes parasités ou non. Quand la partie saillante du pédoncule de l'oeuf de parasitoïde avait été extraite de l'hôte, ce dernier avait été accepté par les femelles. Ceci laisse supposer que la partie saillante du pédoncule de l'oeuf fonctionne comme marqueur externe. Cette partie du pédoncule de l'oeuf a été responsable de la discrimination des hôtes jusqu'à 8 jours après qu'ils aient été parasités, montrant une plus longue efficacité comme marqueur externe que les phéromones externes observées chez d'autres parasitoïdes.

     

Winter survival and oviposition before and after overwintering of a parasitoid wasp, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae)

Winter survival and oviposition before and after overwintering in Ooencyrtus nezarae, an egg parasitoid of phytophagous heteropterans, were examined in Osaka, Japan. Eggs of Riptortus clavatus parasitized by O. nezarae were kept under natural photoperiod and temperature. When honey was supplied, some female adults emerging from early September to late November overwintered. The percentage of overwintering individuals increased as the date of adult emergence advanced. Most female adults supplied with honey and hosts oviposited soon after emergence, then stopped laying eggs. Female adults emerging in mid‐October and early November laid eggs and then overwintered. The induction of diapause in the field seems to vary greatly depending on host availability. Without honey, the survival time of female adults was very short, whether host eggs were supplied or not. After overwintering, most females began to lay eggs in early May if host eggs were supplied, and they produced both male and female progeny. In the study area, a legume field in Osaka, parasitization by O. nezarae was observed from early July to November.     

Parasitoids of Paratachardina lobata (Hem., Kerriidae): surveys for biological control of the invasive lobate lac scale

Paratachardina lobata is an invasive pest in southern Florida, threatening a great number of economically important and native plants. The lobate lac scale does not cause problems in its area of origin, India and Sri Lanka, presumably due to various parasitoid wasps. In an attempt to discover promising parasitoids for biological control against the invasive pest in Florida, P. lobata infesting Pongamia pinnata (Fabaceae) was collected bimonthly from August 2005 to June 2006 at 14 sites in southern India. Four parasitoids were demonstrably associated with P. lobata: a eulophid Aprostocetus bangaloricus Narendran, an encyrtid Ooencyrtus kerriae Hayat and two aphelinids, Marietta leopardina Motschulsky and an undescribed Coccophagus Westwood sp. These chalcidoid wasps were found regularly at all heavily infested sites with an average emergence number per collection period of 62.8, 31.7, 11.9 and 90.5 respectively. The mean number emerged 20–28 days after the collection date, excluding the Coccophagus sp., which occurred significantly later, on average 41 days after collection. Species emergence was examined and parasitized scales dissected. Parasitoid remains were interpreted to understand the mode of parasitism. The Coccophagus sp. was found to be a secondary parasitoid. Marietta leopardina occurred as a primary parasitoid, but only in low number and this species is also known to be hyperparasitic on chalcidoid wasps. Aprostocetus bangaloricus and O. kerriae are promising candidates for the lobate lac scale control in Florida. They are primary parasitoids of P. lobata and occurred at almost every collection site, especially where P. lobata was very abundant.     

THE PREFERENCE AND DENSITY RESPONSES OF EGG PARASITOID,OOENCYRTUS NEZARAE ISHO,TO THE EGGS OF SOYBEAN STICK BUGS,RIPTORTUS CLAVATUS THUNBERG AND PIEZODORUS HYBNERI GMELIN*

Abstract The preference and density response test9 of egg parasitoid, Ooencyrtus nezarae Ishii, to the eggs of soybean stick bugs, Riptortus clavatus Thunberg and Piezodorus hybneri Gmelin, were carried out in this study. In the free choice test, O. nezarae emerged from both eggs of stick bug prefer R. clavatus eggs only in the various ratios of host egg densities. In non‐choice test, O. nezarae emerged from P. hybneri eggs parasitize both R. clavatus and P. hybneri eggs, showing a high parasitism on host eggs. However, O. nezarae reared on R. clavatus eggs had a significantly lower parasitism on the eggs of P. hybneri. Olfactometer test showed that the odor emitted from R. clavatus eggs had a great influence on the host searching and parasitizing behavior of O. nezarae. The number of R. clavatus and P. hybneri eggs parasitized by O. nezarae gradually increased with the increase of host egg densities. However, the parasitism of O. nezarae to R. clavatus eggs decreased with the increase of host density. The parasitism of O. nezarae are significantly lower (P < 0.05) on host egg P. hybneri under the laboratory condition, especially for O. nezarae emerged from R. clavatus eggs. This research results implied that in the soybean field, there were some optimal or spatial barriers for O. nezarae to find R. clavatus eggs efficiently.     

Seasonal history,plant interactions and egg parasitism of the variegated caper bug Stenozygum coloratum Klug (Heteroptera: Pentatomidae)

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Optimal biological parameters for rearing Ooencyrtus pityocampae on the new laboratory host Philosamia ricini

Biological control programmes involving Ooencyrtus pityocampae Mercet (Hymenoptera: Encyrtidae) have proved effective at reducing the damage caused by the pine processionary Thaumetopoea pityocampa Denis & Schiffermüller (Lepidoptera: Thaumatopoeidae). In this study, the biological variables that influence the parasitism of O. pityocampae on the new laboratory host Philosamia ricini Danovan (Lepidoptera: Saturniidae) have been investigated. Laboratory experiments were conducted under the conditions of 25 ± 1°C, 65 ± 5% R.H (relative humidity) and a photoperiod of 16 : 8 h (L : D = light : dark). The host egg age and parasitoid age are often regarded as being key factors influencing the emergence rate of O. pityocampae. The optimal age of host eggs for parasitization was 1–2 days, and the emergence rate was highest with 5‐day‐old female parasitoids. Thus, our results define the optimal conditions for the effective and economic rearing of parasitoids as follows: one 5‐day‐old female parasitoid per 50 (1–2)‐day‐old host eggs. The development time of O. pityocampae ranged between 19.5 and 22.6 days. Parasitoids that were exposed to bio‐honey survived 10.5 times longer than those that did not receive supplemental food. O. pityocampae was reared for more than nine generations on the eggs of P. ricini. Consequently, P. ricini has been found as a suitable new laboratory host for the mass rearing of O. pityocampae for the use of biological control programmes against T. pityocampa in future.     

筛豆龟蝽卵寄生蜂田间发生调查初报

调查表明 ,筛豆龟蝽卵雌虫从 5月初开始产卵 ,5月中旬到 6月底为产卵高峰期 ,接着进入产卵衰退期 ,高峰期产卵量占 80 4%。通过有机毛豆田间标记筛豆龟蝽卵块 ,共发现 2种卵寄生蜂 :卵跳小蜂Ooencyrtussp .和沟黑卵蜂Trissolcussp .。结果发现 :卵跳小蜂是优势种 ,在自然控制因素中起主要的作用。寄生蜂和筛豆龟蝽卵发生动态基本一致 ,寄生蜂数量与寄主卵数量正相关。自然状态下 ,寄生蜂对筛豆龟蝽第 1代卵平均寄生率为 61 3 6%。寄生蜂的羽化集中于毛豆灌浆初期 ,高峰期内 1周羽化量占 81 3 3 %。     

Honeydew feeding increased the longevity of two egg parasitoids of the pine processionary moth

The longevity of a generalist (Ooencyrtus pityocampae) and a specialist (Baryscapus servadeii) egg parasitoid of the pine processionary moth (Thau‐metopoea pityocampa) was compared under laboratory feeding conditions including water and honeydew from aphid species growing on maritime pine (Pinus pinaster) or pedunculate oak (Quercus robur). The longevity of both parasitoid species increased when specimens were fed with honeydew. This increase was larger for the generalist (3.7, 32.0 and 38.0 days) than for the specialist (3.0, 23.3 and 21.5 days) parasitoid species when fed with water, oak and pine aphid honeydew respectively. The phenology of the specialist species B. servadeii is well‐adapted with its host availability with or without food supply. The generalist species O. pityocampae could overlap its host emergence curve during 14.0–20.0 days when fed with oak and pine aphid honeydew respectively, vs. no overlap when no supplementary food was provided. Analysis of honeydew composition indicated that sugars and amino acids may have distinct effects on parasitoid longevity.     

舞毒蛾卵寄生蜂大蛾卵跳小蜂发育与温度的关系及利用替代寄主柞蚕卵繁育的子代品质评价

舞毒蛾Lymantria dispar (L.)是国际性检疫害虫。大蛾卵跳小蜂Ooencyrtus kuwanae (Howard)是舞毒蛾卵的重要寄生蜂, 对舞毒蛾有一定的控制作用。为了在规模化繁育大蛾卵跳小蜂时控制小蜂的发育进度, 设置不同的温度梯度研究了该蜂发育与温度的关系; 同时, 为了对替代寄主繁育出的天敌质量进行评价, 对利用其自然寄主舞毒蛾卵和替代寄主柞蚕Antheraea pernyi卵繁育出的子代成蜂的寿命、 胸宽、 雌雄性比进行了比较。结果显示： 大蛾卵跳小蜂的发育起点温度和有效积温分别为10.50±1.41℃和260.74±25.09日·度, 温度与发育速率的关系为T=10.50+260.74V。当采用30%的蜂蜜水饲喂成蜂时, 柞蚕卵繁育出的大蛾卵跳小蜂雌、 雄蜂的平均寿命分别为15.01和10.38 d, 采用原寄主舞毒蛾卵繁育出的雌、 雄蜂平均寿命分别为20.94和15.95 d, 两者差异显著; 采用柞蚕卵繁育出的雌蜂个体显著大于用舞毒蛾卵繁育出的雌蜂个体; 柞蚕卵和舞毒蛾卵繁育出的大蛾卵跳小蜂雌雄性比没有显著差异, 分别为2.42∶1和2.57∶1。结果表明, 在野外开展舞毒蛾的生物防治时, 释放利用柞蚕卵繁育出的大蛾卵跳小蜂具有可行性。