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.

     

Inter- and intraspecific variation in infectivity ofSteinernema spp. to larvae of the mushroom flyLycoriella solani

Laboratory bioassays were done to assess the susceptibility of larvae of the mushroom sciarid flyLycoriella solani Winnertz (Diptera; Sciaridae) to 16 isolates comprising five species of the entomopathogenic nematode,Steinernema (Nematoda; Steinernematidae). Each isolate was tested by challenging sciarid larvae with single nematodes. Six isolates were also tested in dose-response experiments. Variations in nematode infectivity occurred (p<0.001) at both inter- and intraspecific levels.Steinernema feltiae (Filipjev) was the most virulent species: two isolates, Nemasys (LD₅₀=1.5–3.9) and Sus 94 (1.8–3.9) were superior to the rest.Steinernema kraussei (Steiner) was the least infectious nematode tested as its infection probability never exceeded 0.10. In addition, lethal dose₅₀ values for this species ranged from 9.0–62.6 and two isolates failed consistently to infect any hosts.     

Comparative Assessment of biological (Nematoda: Steinernema feltiae) and chemical methods of control for the mushroom fly Lycoriella auripila (Diptera: Sciaridae)

The sciarid fly Lycoriella auripila is the major pest of mushrooms cultivated in the UK. Its larvae, which are capable of damaging the crop at all stages of production, may cause severe yield losses and can only be controlled with chemical pesticides. An indigenous isolate of the insect‐parasitic nematode Steinemema feltiae was tested as a biological control agent and its effects compared with two commonly used insecticides, diazinon and diflubenzuron. The timing of application of nematodes was found to affect their efficacy. When applied to compost during spawning, nematodes did not significantly reduce fly emergence, but they did if applied at casing when they were almost as effective as diflubenzuron. Diazinon incorporated into compost did not reduce fly emergence and was also the only treatment that did not lower the incidence of mushrooms spoiled by tunnelling of the larvae of L. auripila. When compared with untreated control plots those treated both with diazinon and diflubenzuron showed significant mean losses in yield of 10% in total weight and 17% in total numbers of mushrooms picked. In contrast, when S. feltiae was applied at casing significant mean increases in yield of 7% and 19%, respectively, were attained. Infective nematodes persisted well in casing, very few were found on sporophores.     

Dose- and time-response assessments ofHeterorhabditis heliothidis andSteinernema feltiae [Nem.: Rhabitida] againstAedes aegypti larvae

Steinernema feltiae (=Neoaplectana carpocapsae) andHeterorhabditis heliothidis were tested against 3^rd instarAedes aegypti larvae in the laboratory. Different dosages of the nematodes and varying durations of exposure were assessed.H. heliothidis was more effective thanS. feltiae. Larval mortality showed a positive linear correlation with both nematode dosage and the duration of exposure. The number of nematodes of both species that gained access to the haemocoele of larvae was always low, but increased with dosage and exposure time. The rate of melanization of the nematodes in the larvae was correlated with dosage, but was not affected by the duration of exposure.      

Comparative effects of Steinernema feltiae (Nematoda: Steinernematidae) and insecticides on yield and cropping of the mushroom Agaricus bisporus

In a mushroom crop (Agaricus bisporus) affected by a very low level of sciarid fly (Lycoriella auripila) infestation, the effects of an indigenous isolate of insect-parasitic nematode (Steinernema feltiae) and of two commonly used insecticides (diazinon and diflubenzuron) were studied. When compared with untreated plots, nematodes applied to the casing had no adverse effects on mushroom yields whereas insecticides decreased yields. At a rate of 3 × 10⁶ infective juveniles per tray (surface area = 0.56 m²), S. feltiae elicited increases of 28.5% and 19% in the mean total numbers and weights of mushrooms respectively. Treatment only with diflubenzuron resulted in 14.6% and 6% reductions in mean total numbers and weights of mushrooms, respectively; treatment with both diazinon and diflubenzuron caused 18.5% and 9.4% losses. Application of nematodes generally reduced the mean weight per mushroom whereas insecticides increased it; nematodes delayed the onset of mushroom production (first flush) whereas diflubenzuron delayed the third and fourth flushes. Nematode contamination of sporophores was minimal when S. feltiae was applied at casing. Although their numbers declined with time, the nematodes persisted, in the casing layer, throughout the cropping period of seven weeks. It is concluded that yield benefits associated with nematode application can result mainly from nematode effects on A. bisporus and not solely from suppression of a damaging pest population.     

Population growth kinetics of the nematode, Steinernema feltiae, in submerged monoxenic culture

Monoxenic cultures of the nematode, Steinernema feltiae, were carried out on two complex liquid media: P1, mainly soybean flour/egg yolk/yeast extract, and P2, mainly egg yolk/yeast extract. Up to 140 000–200 000 nematodes ml^–1 were produced within 7 days, and more than 95% of the final population was in the infective juvenile stage. The total nematode concentration growth curve had a sigmoidal shape. Nematode population growth kinetics were modelled using a re-parameterised Gompertz model. Yeast extract concentration appeared to be a key factor for obtaining high nematode concentrations.     

Location of immature stages of the mushroom insect pest Megaselia halterata in mushroom-growing medium

Experiments were conducted to examine the location of oviposition by the phorid fly Megaselia halterata (Wood) (Diptera: Phoridae) in uncased and cased compost. Clearly, a majority of the gravid females choose oviposition sites directly after entering the top layer of the compost. In uncased compost, 60% of all adults emerged from the top of four compost layers of equal thickness. When the compost was covered by a casing layer which was still uncolonized by Agaricus bisporus, oviposition was further concentrated in the top compost layer. In this situation, 91% of all adults emerged from the top compost layer whereas only 1.5% emerged from the casing. When the casing layer was colonized by mushroom mycelium, 45% of all adults emerged from the casing layer and 53% emerged from the top compost layer. Further concentration in the top compost layer and the casing layer occurred as a result of upward migration of larvae. When compost was cased after oviposition, up to 43% of all adults emerged from the casing layer. We concluded that in the control of phorid infestations with insect pathogenic nematodes, applications in uncased compost can be restricted to the upper compost layer. When compost and casing are filled simultaneously, nematode applications in the casing layer only could be considered.     

Selective breeding of Steinernema feltiae (Filipjev) (Nematoda: Steinernematidae) for improved efficacy in control of a mushroom fly,Lycoriella solani Winnertz (Diptera: Sciaridae)

A method of selecting a Steinernema feltiae strain that is effective against a mushroom fly, Lycoriella solani, is described in detail. The pest control efficacy of the selected nematode strain was evaluated and compared with the efficacy of two unselected strains. The selection procedure was designed to give preference to nematode individuals with the greatest ability (1) to search effectively for the target insect larvae in their natural habitat, (2) to infect them shortly after application and (3) to reproduce in their haemocoel. Thirty‐four rounds of selection achieved a 4‐fold improvement in nematode ability to find and parasitize third‐ and fourth‐instar larvae of the pest in the mushroom substrate. In 24‐h laboratory experiments, mortality of the insect caused by nematode juveniles rose from 22.5%, recorded for the original unselected isolate, to 92.5% for the selected strain. In a 51‐day experiment conducted on a mixed age mushroom house population of L. solani, the enhanced pest control ability of the selected strain was detected shortly after nematode application and remained high throughout the experimental period. During the first 4 weeks of the trial the selected nematode strain was significantly better than both unselected strains and caused 91.1–92.7% reduction of the fly emergence from the mushroom substrate. No difference was observed between the efficacy of the selected nematodes applied at 1 × 10⁶ and 3 ×10⁶ infective juveniles per m², while the unselected strains performed significantly better at the higher concentration. All the nematodes examined showed good persistence in the mushroom casing apparently due to recycling in the insect host.     

Evaluation of a genetically selected strain of Steinernema feltiae against the mushroom sciarid Lycoriella mali

The control potential of a strain (ScP) of Steinernema feltiae genetically selected against the mushroom sciarid Lycoriella solani, was evaluated for the management of L. mali. Trials were conducted at two commercial mushroom farms with high and low levels of fly infestation. The efficacy of the ScP strain was compared with the SN strain of S. feltiae and the chitin synthesis inhibitor, diflubenzuron. At low densities of L. mali, the two strains did not differ in efficacy and caused 85–94% reduction in fly populations. At high fly densities with a mixed infestation of the phorid fly, Megaselia halterata, the ScP stain caused 56–83% reduction in L. mali populations whereas the SN strain caused 51–73% reduction. Two doses of the improved strain (0.5 times 10⁶ and 1.0 times 10⁶ infective juveniles per m² cropping area) did not differ in efficacy from diflubenzuron which caused 80% reduction in L. mali populations. The lower dose (0.5 times 10⁶) of the SN strain was less effective than diflubenzuron. The ScP strain had a major advantage over the SN strain in persistence in casing material. Nematodes had no significant effect on mushroom yields.     

Susceptibility of two Coconut Pests,Oryctes rhinoceros [Col.: Scarabaeidae] andTirathaba rufivena [Lep.: Pyralidae], to the entomoparasitic nematodeSteinernema feltiae [= Neoaplectana carpocapsae]

Bioassay indicated that 1 st instar larvae ofOryctes rhinoceros are resistant to infections by the nematodeSteinernema feltiae (estimated LD₅₀: 90 nematodes) but thatTirathaba rufivena larvae larger than 15 mm are highly susceptible (estimated LD₅₀: 3 nematodes). The “All” strain and the “mexican” strain ofS. feltiae gave very similar responses. In a field trial 300,000 nematodes were sprayed on each of 25 palms to controlT. rufivena. Although some mortality from nematodes was observed, the treatment failed to reduce the pest population significantly.     

Selection of insect parasitic nematodes for biological control of the garden chafer,Phyllopertha horticola

Larvae ofPhyllopertha horticola L. (Coleoptera: Scarabaeidae) cause increasing problems on sports fields and lawns in NW-Europe. A biological control programme using insect parasitic nematodes is being developed. This paper contains the results of bioassays with various species and isolates of the nematode generaHeterorhabditis andSteinernema. In bioassays in small pots with moist sand, most of the nematode isolates gave 30–60% mortality against each of the three larval stages. The susceptibility of the grubs for nematode infection generally increased with larval development.H. bacteriophora, H. heliothidis, H. megidis, a DutchHeterorhabditis isolate NLH-E87.3 andS. glaseri 326 showed the highest mortality rates, with nearly 100% mortality of third instar grubs. The DutchHeterorhabditis isolate NLH-E87.3 andS. glaseri 326 were selected as candidates for further studies on their potential as biological control agents forP. horticola grubs in the field.     

Factors affecting progeny production of Anaphes iole

Anaphes iole Girault(Hymenoptera: Mymaridae) is a native, solitaryegg parasitoid of Lygus spp.(Heteroptera: Miridae) in North America. Current research is considering factors thatmay optimize the in-vivo rearing of A.iole using Lygus hesperus Knight(Heteroptera: Miridae) as host. The effects ofhost density, day of oviposition and foodpresence, parasitoid age and mate presence onproduction of A. iole progeny weredetermined in this study. After exposingindividual parasitoids to host patches for 24h, the percentage of hosts containing a latestage A. iole pupa wassignificantly greater at a moderate hostdensity (41–70 eggs per patch) than at a lowdensity (10–40 eggs). But, no differenceswere detected between moderate and high density(71–100 eggs) or between high and low densitytreatments. More adult progeny were generatedby females (of variable age; 0–2 d old) onthe first day of oviposition rather than thesecond day, regardless of food presence. Progeny sex ratio was decidedly male-biased onthe second day. Female age (0 d vs 1 d old)had a marginal effect on production in 24 h; 0d old females tended to generate more adultprogeny than 1 d old females. Overall, thisresearch suggests that exposing newly-emerged,unfed, mated A. iole females to amoderate to high host density for 1 to 2 dcould lead to time-efficient production ofadult progeny in an in-vivo rearing system.     

Control of the mushroom pests Lycoriella auripila (Diptera: Sciaridae) and Megaselia halterata (Diptera: Phoridae) by Steinernema feltiae (Nematoda: Steinernematidae) in field experiments

The nematode Steinernema feltiae (Nematoda: Steinemematidae) was tested for its ability to control two main mushroom pests i.e. the sciarid Lycoriella auripila (Diptera: Sciaridae) and the phorid Megaselia halterata (Diptera: Phoridae) in growing-rooms filled with spawned compost. A clear difference between female and male sciarid control was observed. A nematode application 1 day after casing preceded by an application 1 day before casing on the compost caused an almost complete control (97%) of the F1-generation of female sciarids. The F2-generation of females was similarly controlled (95%) by an application 7 days after casing. A dosage of 1 × 10⁶nematodes m^-2was found to be equally effective as higher dosages. Diflubenzuron remained active throughout entire the cropping period with high sciarid mortality rates varying from 72% to 99%. Phorid control was variable and seemed to depend on the presence of sciarids. In one occasion the control rate of F2-generation phorid larvae was 75% and was possibly caused by the presence of new infective juvenile nematodes recycled in F2-generation sciarid larvae. Diflubenzuron did not significantly reduce phorid numbers.     

Laboratory infection of terrestrial isopods (Crustacea: Isopoda) with neoaplectanid and heterorhabditid nematodes (Rhabditida: Nematoda)

Under laboratory conditions, the nematodes Neoaplectana carpocapsae and Heterorhabditis heliothidis were able to infect and develop inside the hemocoel of terrestrial isopods belonging to the genus Porcellio. Armidillidium vulgare was also infected by N. carpocapsae, but this host was less susceptible than Porcellio. Results show that, under suitable ecological conditions, it would be feasible to utilize N. carpocapsae as a biological control agent of sowbugs (Porcellio spp.). This is the first report showing the ability of neoaplectanids and heterorhabditids to invade representatives of the Crustacea.     

Field Evaluation of Steinernema feltiae Against the Web-spinning Larch Sawfly Cephalcia lariciphila

Field trials were conducted in Rheola Forest, Wales, Great Britain, to determine the effectiveness of Steinernema feltiae UK strain in controlling the web-spinning larch sawfly Cephalcia lariciphila. Foliar sprays at the rate of 5,000-20,000 nematodes/100 cm branch resulted in 3.4-29.4% infection of sawfly larvae. Soil application of 200 nematodes/cm² resulted in 61% infection of sawfly prepupae and 17.3% of pupae. Prepupal infection ranged from 4.8 to 14.7% 1 year after nematode application. Soil applications of this nematode show that it has potential for biological control of sawfly prepupae.     

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana glaseri (Nematoda: Steinernematidae)

The vertical migration of infective juveniles of Neoaplectana glaseri applied to the soil surface or introduced 16 cm below the soil surface was studied in pure silica sand, coarse sandy loam, silty clay loam, and clay. The number of juveniles that migrated and infected wax moth pupae placed in the soil decreased as the proportion of clay and silt increased. The majority of nematodes moved downwards 2-6 cm from the surface, but some penetrated to a depth of 14 cm in pure silica sand and coarse sandy loam. In pure silica sand and coarse sandy loam, nematodes introduced 16 cm below the soil surface were able to infect wax moth pupae located at depths of 0-4 cm and 28-32 cm. Nematodes showed a greater tendency to disperse downwards from the point of application. Movement of the nematode was least in clay soil and limited in silty clay loam soil. The number of migrating nematodes was greatest when wax moth pupae were present.     

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana carpocapsae (Nematoda: Steinernematidae)

The vertical migration of N. carpocapsae infective juveniles applied to the soil surface or introduced 14 cm below the soil surface was studied in four different soil types (pure silica sand, coarse sandy loam, silty clay loam, and clay). The percentage of juveniles able to migrate and infect wax moth pupae placed in the soil decreased as the percentage of clay and silt increased. Most nematodes placed on the soil surface remained within 2 cm of the surface, but some penetrated to a depth of 10 cm in pure silica sand and coarse sandy loam to infect pupae. Some pupae at the same depth were also infected with nematodes in silty clay loam soil. In pure silica sand and coarse sandy loam, nematodes introduced 14 cm below the soil surface were able to infect wax moth pupae located between 4 and 24 cm. Movement was least in clay soil and limited in silty clay loam. Nematodes showed a tendency to disperse upwards from the point of application. In all cases the number of migrating nematodes was greatest when wax moth pupae were present.     

Dynamics of the Entomogenous Nematode Steinernema feltiae Applied to Soil with and without Nematicide Treatment

The dynamics of Steinernema feltiae strain DD-136 in soils with different fauna was investigated to determine the best method for the biological control of soil insects. Infective juveniles (J3) were applied to field plots with and without 1,3-D (Telone II) fumigation. Recovery of J3 and changes in native nematode fauna were monitored until the applied J3 were no longer recovered by Baermann funnel (BF). Recovery of J3 by BF or by a two-step extraction procedure from steam-sterilized or nonsterilized sandy or silty soil with different fauna was investigated. More DD-136 J3 were recovered from the 1,3-D treated soil than from nontreated soil, while native nematodes in the treated soil fluctuated more with the addition of DD-136 than those in nontreated soil. The J3 persisted longer in silty than in sandy soils. The inundative soil application of DD-136 increased native rhabditids and decreased plant-parasitic nematodes. DD-136 in chemically treated soil not only effectively attacked the invading soil insect pests but also suppressed the recovery of plant nematodes.     

Effects of Application Rates of Steinernema feltiae (Nematoda: Steinernematidae) on Biological Control of the Mushroom Fly Lycoriella auripila (Diptera: Sciaridae)

The potential of Steinernema feltiae for the biological control of Lycoriella auripila was tested in commercial mushroom‐growing conditions. The nematodes, applied at rates of 1.5, 3, 6 or 12 x 10 ⁶ infective juveniles per 34 kg tray of spawn‐run compost, were mixed into the casing material before it was spread over the compost surface. When compared with untreated control trays, any rate of nematode application significantly reduced fly emergence. Insecticides significantly reduced mushroom yields; nematodes significantly increased them. At a rate of 3 x 10 ⁶ infectives/tray S. feltiae elicited mean total increases in the weight and numbers of mushrooms produced of 8% and 11% respectively. The nematodes also reduced the incidence of mushrooms spoiled by tunnelling sciarid larvae. The early decline in the numbers of nematodes persisting in casing was a trend that was reversed later, when evidence was obtained that S. feltiae was recycling in insects that had been killed. When applied at a rate of 3 ‐10⁶infectives/tray of compost S. feltiae should provide reliable and cost‐effective biological control of L. auripila.