Differential susceptibility of lepidopterous pupae to infection by the nematode Neoaplectana carpocapsae

Prepupae of Galleria mellonella, Spodoptera exigua, and Pseudaletia unipuncta were highly susceptible to infection by the nematode Neoaplectana carpocapsae and its associated bacterium, Xenorhabdus nematophilus. On the other hand, pupae of the three species were significantly different in their susceptibility to the nematode. G. mellonella pupae were highly susceptible (100% mortality), S. exigua pupae were moderately susceptible (ca. 75% mortality), and P. unipuncta pupae were least susceptible (ca. 54% mortality). In the latter two species, many pupae died without any nematode development, but the typical signs associated with a nematode infection were evident. Age of the pupae and increasing the dosage of the nematode did not significantly affect mortality of S. exigua or P. unipuncta.     

Susceptibility of Hoplia philanthus (Coleoptera: Scarabaeidae) larvae and pupae to entomopathogenic nematodes (Rhabditida: Steinernematidae, Heterorhabditidae)

Biological control potential of nine entomopathogenic nematodes, Heterorhabditis bacteriophora CLO51 strain (HbCLO51), H. megidis VBM30 strain (HmVBM30), H. indica, Steinernema scarabaei, S. feltiae, S. arenarium, S. carpocapsae Belgian strain (ScBE), S. glaseri Belgian strain (SgBE) and S. glaseri NC strain (SgNC), was tested against second-, and third-instar larvae and pupae of Hoplia philanthus in laboratory and greenhouse experiments. The susceptibility of the developmental stages of H. philanthus differed greatly among tested nematode species/strains. In the laboratory experiments, SgBE, SgNC, HbCLO51 and HmVBM30 were highly virulent to third-instar larvae and pupae while SgBE was only virulent to second-instar larvae. Pupae were highly susceptible to HbCLO51, HmVBM30, SgBE and SgNC (57–100%) followed by H. indica and S. scarabaei (57–76%). In pot experiments, HbCLO51, SgBE and S. scarabaei were highly virulent to the third-instar larvae compared to the second-instar larvae. Our observations, combined with those of previous studies on other nematode and white grub species, show that nematode virulence against white grub developmental stages varies with white grub and nematode species.     

Factors affecting entomophilic activity of Neoaplectana feltiae in mushroom compost

The host-searching ability of Neoaplectana feltiae Filipjev (= S. bibionis Bovien) (Nematoda: Steinernematidae) in response to larvae of a mushroom fly, Lycoriella solani Winn. was examined in a mushroom substrate. Individuals of L. solani were less attractive for the parasite than larvae of Galleria mellonella L. The nematode juveniles penetrated a 22 cm layer of casing mixture within 2–4 days. In the casing alone nematode effectiveness was better than in mushroom compost or in compost and casing together. In the casing mixture parasite dosages of 20 and 100 juveniles per cm² led to 22% and 45% parasitization of L. solani respectively, while all G. mellonella larvae were parasitized at both dosages. The prevalence of nematode infection depended on the content of water in the mushroom substrate. The highest N. feltiae infectivity was observed, when the ratio of the dry casing weight to the weight of water content was 1: 2.5. The practical aspects of the observed phenomena, essential for the use of N. feltiae in the protection of commercial mushroom cultivation are discussed.     

Susceptibility of the filbertworm (Cydia latiferreana, Lepidoptera: Tortricidae) and filbert weevil (Curculio occidentalis, Coleoptera: Curculionidae) to entomopathogenic nematodes

The objective of this study was to determine the susceptibility of the two primary direct insect pests of hazelnuts in Oregon to three species of entomopathogenic nematodes. The entomopathogenic nematodes (Heterorhabditis marelatus Pt. Reyes, Steinernema carpocapsae All and Steinernema kraussei L137) were used in laboratory soil bioassays to determine their virulence against filbertworm, Cydia latiferreana (Walsingham) (Lepidoptera: Tortricidae) and filbert weevil, Curculio occidentalis (Casey) (Coleoptera: Curculionidae). All three nematode species were infective in laboratory bioassays. Infectivity ranged from 73-100% and 23-85% for filbertworm and filbert weevil, respectively. Field results were similar to those found in the laboratory with filbertworm larvae being more susceptible to nematode infection.     

Parasitism of Western Corn Rootworm Larvae and Pupae by Steinernema carpocapsae

Virulence and development of the insect-parasitic nematode, Steinernema carpocapsae (Weiser) (Mexican strain), were evaluated for the immature stages of the western corn rootworm, Diabrotica virgifera virgifera LeConte. Third instar rootworm larvae were five times more susceptible to nematode infection than second instar larvae and 75 times more susceptible than first instar larvae and pupae, based on laboratory bioassays. Rootworm eggs were not susceptible. Nematode development was observed in all susceptible rootworm stages, but a complete life cycle was observed only in second and third instar larvae and pupae. Nematode size was affected by rootworm stage; the smallest infective-stage nematodes were recovered from second instar rootworm larvae. Results of this study suggest that S. carpocapsae should be applied when second and third instar rootworm larvae are predominant in the field.     

The entomogenous nematode Neoaplectana bibionis as a biological control agent of Agrotis segetum in lettuce

Biological control of the soil-inhabitating larvae (cutworms) of Agrotis segetum Schiff. using the entomogenous nematode Neoaplectana bibionis Bovien was investigated under field conditions. Cutworms were introduced to plots planted with lettuce, Lactuca sativa L. After planting and infection with cutworms the plots were treated with either N. bibionis, the insecticide endosulfan or water. The trials were sited on locations with loamy and sandy soil. Adequate control of cutworms was obtained using 2.5×10⁵ nematodes/m² on sandy soil and 1×10⁶ nematodes/m² on loamy soil. Effects of these treatments with nematodes were equal to the effect of endosulfan.

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Neoaplectana bibionis ein entomophager nematode zur biologischen bekämpfung von Agrotis segetum an salat

Zusammenfassung Unter Freilandbedingungen wurde die biologische Bekämpfung von Erdraupen (Agrotis segetum Schiff., Lepidoptera, Noctuidae) mit dem entomophagen Nematoden Neoaplectana bibionis Bovien geprüft. Mit Salat bepflanzte Parzellen wurden mit Erdraupen besetzt. Anschliessend wurde auf die Parzellen N. bibionis, das Insektizid Endosulfan oder Wasser ausgebracht. Die Versuche wurden in Gebieten mit lehmigen und sandigen Böden durchgeführt. Für eine ausreichende Bekämpfung der Erdraupen waren auf dem sandigen Boden 2.5×10⁵ Nematoden/m² und auf dem lehmigen Boden 1×10⁶ Nematoden/m² erforderlich. Die Wirkung dieser Behandlungen entsprach der mit Endosulfan.

     

大豆田3种赤眼蜂对大造桥虫卵的寄生适应性

大造桥虫是我国大豆生产上最主要的食叶类害虫之一,目前关于这种害虫的生物防治鲜有报道。本文比较研究了大豆田三种赤眼蜂对大造桥虫卵的寄生能力和发育适合度。研究结果表明,单头黏虫赤眼蜂24 h平均寄生13.1粒卵,明显高于玉米螟赤眼蜂(1.1粒)和螟黄赤眼蜂(0.8粒)。三种赤眼蜂寄生大造桥虫卵后,均能顺利完成发育,羽化率为63.2%-74.2%,发育历期为10.6-10.8 d,三者间均不存在显著差异,但黏虫赤眼蜂的后代雌蜂比率(57.2%)明显高于其它二种赤眼蜂。本研究为豆田释放黏虫赤眼蜂同时生物防治多种害虫提供了理论依据。     

Parasitism of the mosquito Culex pipiens by the nematode Heterorhabditis bacteriophora

Various concentrations of the nematode Heterorhabditis bacteriophora were added to dishes containing second, third, and fourth larval instars of the mosquito, Culex pipiens, respectively. The infective stage nematodes were ingested by the mosquito larvae, they then penetrated through the alimentary tract in the neck region and entered the hemocoel. A melanization reaction killed many invading nematodes, but heavier concentrations overwhelmed the hosts' defense reaction and 100% mortality of third- and fourth-instar larvae was achieved using between 170 and 200 nematodes per host. Death was either due to the nematode releasing cells of the symbiotic bacterium, Xenorhabdus luminescens, into the hemocoel or to foreign bacteria (mostly Pseudomonas aeruginosa), which were introduced by the penetrating nematodes. The potential use of this nematode as a biological control agent of larval culicine mosquito is discussed.     

Moisture requirements of the DD-136 strain of Neoaplectana carpocapsae (Nematoda; Rhabditida) as related to host infection

The DD-136 strain of Neoaplectana carpocapsae is capable of continued movement over dry surfaces at 35 and 5 C if relative humidity (RH) ranges above 90%. It can also live in the field on foliage for several hours at night and up to 24 days in bark beetle tunnels in pine bolts.Further nematode research should be directed toward a few insect species where precipitation and RH are suitable for the dispersion of the dauerlarvae. Such areas in the US are located in the Southeast, Northeast, and on the Northwest Coast.     

Parasitism of Kenyan Mosquito Larvae (Diptera: Culicidae) by Romanomermis culicivorax (Nematoda: Mermithidae)

The ability of Romanomermis culicivorax to infect, develop, and emerge from Kenyan mosquito hosts was evaluated in the laboratory. Host species tested were Aedes aegypti, Ae. dentatus, Ae. hirsutus, Anopheles arabiensis, An. coustani, An. funestus, An. gambiae, An. pharoensis, Culex duttoni, Cu. ethiopicus, Cu. poicilipes, Cu. quinquefasciatus, Cu. tigripes, Cu. univittatus, Coquillettidia metallica, Mansonia africana, Ma. uniformis, Mimomyia splendens, Mi. uniformis, Toxorhyncites brevipalpis, and Uranotaenia balfouri. R. culicivorax penetrated all the host species tested and developed and emerged from most of the hosts. Both penetration and some development, but not nematode emergence, were observed from all instars of Ma. uniformis. T. brevipalpis exhibited signs of resistance in the form of melanization of R. culicivorax within 48 hours of infection in all four instar stages. Nematode melanization, especially in older hosts, was observed in Ae. dentatus, Ae. hirsutus, Cu. duttoni, Cu. tigripes, and Mi. splendens. When melanization occurred, the melanized carcass of the nematode was passed on from instar to instar. The implications for field release of R. culicivorax in Kenya are still good, especially in habitats where different mosquito species occupy the same niche at different times, which would allow for nematode recycling.     

The pathogenicity of Neoaplectana carpocapsae to blackfly larvae

Laboratory assays indicated that infective-stage juveniles of Neoaplectana carpocapsae are highly pathogenic to Simulium spp. larvae. Instar susceptibility increased with larval size, with early instars being nonsusceptible. High rates of mortality (75 – 100%) were achieved in assays against late instars. These results indicate that N. carpocapsae may have potential value as a blackfly biocontrol agent.     

昆虫病原线虫对草原毛虫幼虫的致病力

草原毛虫Gynaephora alpherakii是青藏高原草原的主要害虫。国家明令禁止使用化学药剂防控这一害虫。因此,有必要以生物农药控制这种害虫。本试验室内测定5种昆虫病原线虫（Steinernema longicaudum X-7,S. carpocapsae All,S. feltiae SN,Heterorhabditis bacteriophora H06和H. indica LN2）对草原毛虫的致病力。结果表明,S. carpocapsae All、S. feltiae SN两种线虫对草原毛虫的侵染效果较好。适宜S. carpocapsae All、S. feltiae SN线虫的侵染活动的环境温度为25℃;低温环境下两种线虫随着剂量的提高,对草原毛虫的致病力均有着显著地增长（P<0.05）,且S. feltiae SN线虫的活性高于S. carpocapsae All线虫。因此,昆虫病原线虫S. feltiae SN品系具有效防治青藏高原高寒草地草原毛虫的应用潜力。     

Effect of Density and Extra Dung on Brood Parasitism in the Dung Beetle, Onthophagus Taurus

Kleptoparasitism has not been well documented in insects and intraspecific brood parasitism is even less well known. This study examines the effect of extra resources and density on the probability of kleptoparasitism in the bull headed dung beetle Onthophagus taurus. A high level (>60 %) of kleptoparasitism was found across all treatments and suggest that although density may not affect the probability to kleptoparasitize, it may influence brood ball production. This study also documents for the first time that male O. taurus kleptoparasitize.     

Pea Lectin Expressed Transgenically in Oilseed Rape Reduces Growth Rate of Pollen Beetle Larvae

In several studies plant lectins have shown promise as transgenic resistance factors against various insect pests. We have here shown that pea seed lectin is a potential candidate for use against pollen beetle, a serious pest of Brassica oilseeds. In feeding assays where pollen beetle larvae were fed oilseed rape anthers soaked in a 1% solution of pea lectin there was a reduction in survival of 84% compared to larvae on control treatment and the weight of surviving larvae was reduced by 79%. When a 10% solution of pea lectin was used all larvae were dead after 4 days of testing. To further evaluate the potential use of pea lectin, transgenic plants of oilseed rape (Brassica napus cv. Westar) were produced in which the pea lectin gene under control of the pollen-specific promoter Sta44-4 was introduced. In 11 out of 20 tested plants of the T₀-generation there was a significant reduction in larval weight, which ranged up to 46% compared to the control. A small but significant reduction in larval survival rate was also observed. In the T₂-generation significant weight reductions, with a maximum of 32%, were obtained in 10 out of 33 comparisons between transgenic plants and their controls. Pea lectin concentrations in anthers of transgenic T₂-plants ranged up to 1.5% of total soluble protein. There was a negative correlation between lectin concentration and larval growth. Plants from test groups with significant differences in larval weights had a significantly higher mean pea lectin concentration, 0.64% compared to 0.15% for plants from test groups without effect on larval weight. These results support the conclusion that pea lectin is a promising resistance factor for use in Brassica oilseeds against pollen beetles.     

Host specificity of entomophilic nematodes—A review

Entomophilic nematodes can be biologically manipulated either as biological control agents or as biological insecticide agents. The characteristics, mode of application, and degree of specificity for each of these is considered. The importance of host specificity information for nematode parasites potentially useful in controlling insect pests is emphasized. A general discussion of host specificity and the factors influencing host specificity of entomophilic nematodes is presented.Characteristics of nematodes of the genus Heterotylenchus are discussed while particular emphasis is placed on H. autumnalis, a potentially useful biological control agent of the face fly, Musca autumnalis. Greater detail of the bionomics of this nematode, its attributes and disadvantages as a successful control agent are considered. The factors resulting in host specificity of this parasite, especially host resistance, in Musca domestica, Orthellia caesarion, and Ravinia l'herminieri, are encapsulation and melanization.It is emphasized that biological control workers are working with a dynamic, evolving host-parasite system and that really they are faced with the same problems (resistance of the host and target specificity of the applied material) originally and still confronting the toxicologist and economic entomologist.     

Local Competition Between Foraging Relatives: Growth and Survival of Bruchid Beetle Larvae

Kin selection theory states that when resources are limited and all else is equal, individuals will direct competition away from kin. However, when competition between relatives is completely local, as is the case in granivorous insects whose larval stages spend their lives within a single seed, this can reduce or even negate the kin-selected benefits. Instead, an increase in competition may have the same detrimental effects on individuals that forage with kin as those that forage with non-kin. In a factorial experiment we assessed the effects of relatedness and competition over food on the survival and on fitness-related traits of the bruchid beetle Callosobruchus maculatus. Relatedness of competitors did not affect the survival of larvae. Larval survival substantially decreased with increasing larval density, and we found evidence that beetles maturing at a larger size were more adversely affected by competition, resulting in lower survival rates. Furthermore, females showed a reduction in their growth rate with increasing larval density, emerging smaller after the same development time. Males increased their growth rate, emerging earlier but at a similar size when food was more limited. Our results add to the growing number of studies that fail to show a relationship between relatedness and a reduction in competition between relatives in closed systems, and emphasize the importance of the scale at which competition between relatives occurs.