Investigations on the parasitism ofOtiorrhynchus salicicola andO. Sulcatus [Col.: Curculionidae] byHeterorhabditis sp. [Nematoda]

Experiments were conducted to study the efficacy of the insect parasitic nematodeHeterorhabditis sp. (HW79) as a biological control agent ofOtiorrhynchus salicicola. This weevil species is reported as a pest of ornamental plants in Switzerland and Italy. Dipping plastic boxes containing heavily infested cuttings of laurel (Prunus laurocerasus) in a nematode suspension resulted in approximately 100% parasitisation of full-grown larvae, pupae and non-emerged young adults. The average dose resulting from dipping varied between 56,000 and 62,000 nematodes per liter soil. This experiment was run under natural outdoor conditions. In a further outdoor experiment, pottedLigustrum plants were inoculated with eggs ofO. salicicola and later 20,000 infective juvenile nematodes per liter soil were added to the soil surface. The resulting weevil mortality in the treated pots was 78%. In seven greenhouse tests using the same nematode dose in pots with horticultural soil to which weevil larvae had been added, weevil mortality varied between 76% and 100%, the arithmetic average being 90%. These results indicate that Heterorhabditid nematodes may provide an effective means of controllingO. salicicola. In an other experiment usingO. sulcatus larvae, the influence of application time on nematode efficacy was investigated. When nematodes were added a few days before weevil larvae had hatched from the eggs, no parasitic effect was obtained. Nematode applications done shortly after larval hatching however, resulted in complete weevil control. These results are of significance in timing nematode applications in practice.      

Use of a nematode, Heterorhabditis heliothidis, to control black vine weevil, Otiorhynchus sulcatus, in potted plants

Application of aqueous suspensions of infective juvenile Heterorhabditis heliothidis, isolate T327, to the soil resulted in up to 100% parasitisation of larvae of the black vine weevil, Otiorhynchus sulcatus, in potted yew, raspberries and grapes in nurseries, and over 87% parasitisation on potted cyclamens and strawberries. Pupae and newly emerged adults on grapevines were also parasitised. Another isolate, T310, produced 92.5 to 98.5% parasitism of O. sulcatus larvae on potted cyclamens in glasshouse, but was less effective on strawberries. Neoaplectana bibionis was found to be less effective than H. heliothidis T327 strain. The use of these nematodes provides an economical and effective method for controlling O. sulcatus on potted plants in glasshouses and nurseries.     

Effects of a novel microsporidium on the black vine weevil, Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae)

A newly discovered microsporidium infecting the black vine weevil, Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae), provisionally placed in the genus Canningia, was studied to determine its impact on O. sulcatus. O. sulcatus populations from several locations were sampled and evaluated for microsporidiosis. A very low prevalence of the disease was observed in all locations surveyed (<3.0%). Laboratory studies were conducted by orally exposing both larvae and adults of O. sulcatus to varying concentrations of Canningia sp. spores. Larval bioassays at a variety of dosages (0, 10, etc.) were performed to evaluate pathogen infectivity, larval survival and growth. Adult bioassays (dosages: 0, 10, etc.) were performed to evaluate longevity, fecundity and mechanisms of vertical pathogen transmission. Larvae and adults were infected in all spore treatments. Larval growth was significantly reduced at dosages above 10 spores/larva. Adults infected at all dosages experienced high levels of mortality and fecundity was reduced to zero. Greenhouse trials were performed to determine if larvae feeding in soil acquired infections when spores were topically applied as a drench application (0, 10⁵, 10⁶, 10⁷ spores/pot). Established larvae feeding on plant roots in pots developed infections when exposed to drench treatments of 10⁶ and 10⁷ spores/pot after 14-21 days. Canningia sp. is an acute pathogen of O. sulcatus infective to both larvae and adults. Topically applied spores also infected larvae feeding on roots in soilless potting media, suggesting the possibility of using this pathogen in a microbial control program.     

Impact of predatory carabids on below- and above-ground pests and yield in strawberry

The impact of adult carabid beetles on below- and above-ground pests and fruit yield was examined in the laboratory and a two-year strawberry field study. In the laboratory, adults of Carabus nemoralis Muller, Nebria brevicollis (F.), Pterostichus algidus LeConte, Pterostichus melanarius (Illiger), and Scaphinotus marginatus Fischer (Coleoptera: Carabidae) consumed black vine weevil, Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae) eggs, larvae and/or pupae placed on the surface. The same five carabid species showed no impact or low removal rates of O. sulcatus larvae that had burrowed into the root of potted strawberry plants. In an assay with only P. melanarius, adults consumed O. sulcatus larvae placed on the soil surface more frequently than larvae buried 1.3 or 5?cm below. In a field study, the density of adult carabids, predominantly P. melanarius, was manipulated with augmented, exclusion, and open control plots (2?×?2?m). Manipulating carabid density had no impact on the removal of sentinel O. sulcatus larvae and pupae that were buried belowground which is consistent with laboratory observations. Increasing carabid density within augmented plots led to greater removal of red clover seeds, Trifolium pratense L., placed on the soil surface in the first?year. Decreasing carabid density within exclusion plots resulted in fewer marketable fruits compared to control plots in both years. These results suggest that certain adult carabids may have limited impact belowground, and some beneficial impacts above-ground with pest control and crop protection.     

Behavioural response of Heterorhabditis megidis towards plant roots and insect larvae

The behavioural response of infective juveniles (IJs) of Heterorhabditis megidis (strain NLH-E87.3) to cues from roots of strawberry (Fragaria x ananassa Duch.), thuja (Thuja occidentalis L.) and to larvae of the black vine weevil, Otiorhynchus sulcatus, was studied. Choice assays were conducted in an Y-tube olfactometer filled with moist sand. Infective juveniles were activated by the presence of intact roots of both strawberry and thuja plants. Some nematodes aggregated in the compartments with roots but most moved away from the roots to the opposite side. Given a choice, IJs showed a preference for strawberry roots above O. sulcatus larvae. No difference in preference was observed between thuja roots and O. sulcatus larvae. The combination of strawberry roots with vine weevil larvae was preferred above roots alone. In the assays with thuja roots and larvae versus thuja roots alone, however, IJs were stimulated to move but showed preference for the opposite compartment away from the arms with roots and larvae. Nematodes responded differently to mechanically damaged roots as opposed to roots damaged by vine weevil larvae. In assays with damaged thuja roots, IJs were most attracted by the roots damaged by larvae, whereas in the strawberry assays IJs showed a clear preference for the mechanically damaged roots. When challenged with a choice between strawberry and thuja roots, IJs moved preferentially to strawberry than to thuja roots. A preference for the combination of strawberry roots plus larvae over the thuja roots plus larvae was also observed.     

Light spectra blocking films reduce numbers of western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae) in strawberry,Fragaria x ananassa

1. Frankliniella occidentalis is a pest of horticultural crops, including commercial strawberry (Fragaria x ananassa). Control is challenging because certain populations are resistant to insecticides and, in strawberry, now relies on the application of biocontrols. However, this approach is not always successful if F. occidentalis populations overwhelm biocontrols. We investigated whether targeted spectral modifications to cladding materials could reduce numbers of F. occidentalis, in strawberry flowers.
2. Five UV-attenuating plastic-film materials were tested in three, 6-week, semi-field tunnel experiments containing strawberry plants. F. occidentalis were introduced into tunnels from a laboratory culture and subsequent numbers that developed in strawberry flowers were recorded.
3. Limiting UV-A radiation to the crop significantly reduced the numbers of adult and larval F. occidentalis in strawberry flowers. The numbers of adult (and larvae) in flowers were reduced by 42 (47)%, 54 (41)%, 70 (73)%, and 82 (73)% in UV350, UV370, UV400, and UV430-attenuating films, respectively, compared with the UVopen (control) film. However, no damage to strawberry fruits was observed regardless of the film treatment.
4. Incorporating UV-attenuating films as tunnel cladding can suppress F. occidentalis numbers in strawberry. Reducing populations of F. occidentalis in crops is likely to enable the more successful use of other non-chemical control strategies.

     

Influences of host size and host species on theinfectivity and development of Heterorhabditismegidis (strain NLH-E87.3)

The infectivity, time to first emergence of infective juveniles (IJs), total number of IJs per insect and IJs body length of the entomopathogenic nematode Heterorhabditis megidis (strain NLH-E87.3) after development in larvae of two insect hosts, Galleria mellonella (greater wax moth) and Otiorhynchus sulcatus (vine weevil) was studied. At a dose of 30 IJs, larvae of G. mellonella show to be significantly more susceptible than O. sulcatus larvae. At a dose of one IJ, vine weevil larvae were more susceptible. The number of invading infective juveniles (IJs) increased with host size while the host mortality at a dose of one IJ decreased with the increase of host size. Time to first emergence was longer at a dose of one IJ per larva and increased with the increase of host size in both insect species. Reproduction of IJs differed between host species, host sizes and doses of nematodes. Generally, the IJs body size increased with an increasing host size. The longest infective juveniles were produced at the lowest IJ doses. Results are discussed in relation to the influence of different host species and their different sizes on the performance of H. megidis (strain NLH-E87.3) as a biological control agent.     

Modelling temperature-dependent development and survival of Otiorhynchus sulcatus (Coleoptera: Curculionidae)

Abstract 1 We conducted a laboratory experiment to quantify the stage‐specific effects of temperature on development time and survival of Otiorhynchus sulcatus (Fabricius) (Coleoptera: Curculionidae), a serious economic pest of horticultural crops. Quantification of the relationship between stage development and temperature is required to predict seasonal occurrence of particular life stages and to optimize the timing of monitoring and control tactics. 2 Temperature‐dependent survival rate was quantified using an extreme value function and showed a skewed bell shape, due to the vulnerability of the insect to high temperature in all stages. 3 The development times of O. sulcatus decreased with increasing temperature up to 27 °C for eggs and 24 °C for larvae and pupae. The nonlinear relationship between development rate and temperature was described using the Logan model, and enabled us to estimate the optimum temperature for development. 4 The inherent variation of development time was estimated from the cumulative frequency of stage emergence, which was modelled using the cumulative Weibull function. 5 The stage emergence model, which simulated the transition from one stage to the next in relation to temperature and cohort age, was constructed by incorporating stage‐specific survival and development rate submodels with the Weibull model of stage frequency. 6 Our results show a difference in optimal temperature regime among developmental stages of O. sulcatus.     

Insecticide‐induced hormesis in an insecticide‐resistant strain of the maize weevil,Sitophilus zeamais

Sublethal responses to insecticides are frequently neglected in studies of insecticide resistance, although stimulatory effects associated with low doses of compounds toxic at higher doses, such as insecticides, have been recognized as a general toxicological phenomenon. Evidence for this biphasic dose–response relationship, or hormesis, was recognized as one of the potential causes underlying pest resurgence and secondary pest outbreaks. Hormesis has also potentially important implications for managing insecticide‐resistant populations of insect‐pest species, but evidence of its occurrence in such context is lacking and fitness parameters are seldom considered in these studies. Here, we reported the stimulatory effect of sublethal doses of the pyrethroid insecticide deltamethrin sprayed on maize grains infested with a pyrethroid‐resistant strain of the maize weevil (Sitophilus zeamais) (Coleoptera: Curculionidae). The parameters estimated from the fertility tables of resistant insects exposed to deltamethrin indicated a peak in the net reproductive rate at 0.05 ppm consequently leading to a peak in the intrinsic rate of population growth at this dose. The phenomenon is consistent with insecticide‐induced hormesis and its potential management implications are discussed.     

Effects of combining microbial and chemical insecticides on mortality of the Pecan Weevil (Coleoptera: Curculionidae)

The pecan weevil, Curculio caryae (Horn), is a key pest of pecan [Carya illinoinensis (Wangenh.) K. Koch]. Current control recommendations are based on chemical insecticide applications. Microbial control agents such as the entomopathogenic nematode, Steinernema carpocapsae (Weiser) and the fungus Beauveria bassiana (Balsamo) Vuillemin occur naturally in southeastern U.S. pecan orchards and have shown promise as alternative control agents for C. caryjae. Conceivably, the chemical and microbial agents occur simultaneously within pecan orchards or might be applied concurrently. The objective of this study was to determine the interactions between two chemical insecticides that are used in commercial C. caryae control (i.e., carbaryl and cypermethrin applied below field rates) and the microbial agents B. bassiana and S. carpocapsae. In laboratory experiments, pecan weevil larval or adult mortality was assessed after application of microbial or chemical treatments applied singly or in combination (microbial + chemical agent). The nature of interactions (antagonism, additivity, or synergy) in terms of weevil mortality was evaluated over 9 d (larvae) or 5 d (adults). Results for B. bassiana indicated synergistic activity with carbaryl and antagonism with cypermethrin in C. caryae larvae and adults. For S. carpocapsae, synergy was detected with both chemicals in C. caryae larvae, but only additive effects were detected in adult weevils. Our results indicate that the chemical-microbial combinations tested are compatible with the exception of B. bassiana and cypermethrin. In addition, combinations that exhibited synergistic interactions may provide enhanced C. caryae control in commercial field applications; thus, their potential merits further exploration.     

Microbial control of cotton pests: use of the naturally occurring entomopathogenic fungus Aspergillus sp. (BC 639) in the management of Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae) and beneficial insects on transgenic cotton crops

The commercial adoption of transgenic Bacillus thuringiensis (Bt) cotton (Bollgard II®) reduced the use of insecticides to control Helicoverpa spp. However, the ineffectiveness of the Bt toxin against sucking pests such as silverleaf whiteflies (Bemisia tabaci) resulted in a marked increase in B. tabaci populations and in the use of insecticides to control this pest. The effect of the entomopathogenic fungus Aspergillus sp. BC 639 on B. tabaci and beneficial insects (predominantly predatory insects) was studied in commercial cotton field trials. The results showed that oil-based extracts of the entomopathogenic fungus BC 639 control the number of B. tabaci adults and nymphs in commercial transgenic cotton crops. The BC 639 fungus caused 60.0%, 67.2%, and 68.8% mortality in adults, and 54.6%, 62.3%, and 51.7% in nymphs at 7, 14, and 21 days after treatment, respectively, relative to the unsprayed controls. The effect of BC 639 at concentrations of 125, 250, and 500?ml/ha on low-density B. tabaci (～10 nymphs/leaf) did not differ significantly from that of the commercial insecticide (pyriproxifen). However, at higher densities (>50 nymphs per leaf), low concentrations of BC 639 (125 and 250?ml/ha) were not as effective as 500?ml/ha BC 639 in successfully controlling the pest. A simple graphic analysis suggested that the more B. tabaci nymphs per leaf, the fewer adults per leaf, and that once the number of nymphs increased to ～70 per leaf, a negative feedback regulatory effect reduced the survivorship of the nymphs and adults and/or caused the emigration of the adults from the contaminated leaves in search of new resources. Therefore, the ability of BC 639 to control B. tabaci adults and nymphs with minimal effects on predatory insects indicates its potential utility in supplementing integrated pest management programmes for cotton crops.     

Foraging behavior responses of Orius insidiosus to thrips cues

The minute pirate bugs (Hemiptera: Anthocoridae) are effective biological control agents against destructive agricultural pests such as the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) in agroecosystems around the world. One species, Orius insidiosus (Say), has proven effective in controlling thrips populations in fields and greenhouses, and serves as an integral component of many integrated pest management (IPM) programs. Three experiments were conducted using motion-tracking software and dual-choice Y-tube bioassays to determine whether direct thrips contact and thrips cues contact induced arrestant and attractant behaviors. The experiments revealed that O. insidiosus adults exhibited behavioral changes indicative of switching from extensive to intensive foraging after direct exposure to thrips prey. Similar arresting behavior was induced by the presence of thrips tracks alone. In Y-tube bioassays O. insidiosus showed preference towards arms containing tracks from western flower thrips larvae vs. clean arms, but only when direct contact with the tracks was made in the stem. Our data indicate that thrips deposit non-volatile semiochemicals that are used by O. insidiosus during foraging. These compounds have the potential to aid in O. insidiosus behavior manipulation which may help in early control of thrips populations in fields and greenhouses. Further research is necessary to determine the chemical composition of these cues and how to effectively and pragmatically integrate the inducing stimuli into biocontrol programs as part of IPM strategies.     

A review on biological interactions and management of the cotton bollworm,Helicoverpa armigera (Lepidoptera: Noctuidae)

Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is one of the most damaging insect pests globally, causing estimated global economic losses of over 3 billion US dollars annually. Crops most affected include cotton, tomato, soybean, grain crops such as corn and sorghum, chickpea and other pulses. Adults of this species possess strong migratory abilities (>2000 km), high fecundity and rapid reproductive rates; completing 4–6 generations per year in most cropping regions. Furthermore, the larvae are polyphagous, with a wide and diverse host range and possess the ability to enter diapause in order to survive adverse climatic conditions. At present, it is distributed across most of Oceania, Asia, Africa and southern Europe and has recently spread to South America. Various control measures have been trialled or proposed for the treatment of this pest, including synthetic insecticides, phytopesticides, microbial pesticides, macro-biocontrol agents (both parasitoids and predators) and the development of genetically modified crops (e.g. Bt cotton). Successful control necessitates the use of an integrated pest management (IPM) approach, wherein biological, chemical and physical control measures are combined for the greatest control efficacy.     

Review of entomopathogenic fungi and nematodes as biological control agents of tephritid fruit flies: current status and a future vision

Several fruit fly species (Diptera: Tephritidae) are invasive pests that damage the quality of fruits in horticultural crops and cause significant value losses worldwide. Management of fruit flies mainly depends on conventional insecticides. Unfortunately, the application of synthetic insecticides has caused environmental pollution, risks for humans and animals, and development of resistance. Furthermore, controlling fruit flies by applying synthetic insecticides is challenging because fruit containing third instars often fall from the tree – subsequently the larvae leave the decaying fruits and pupate in the soil. Consequently, both larvae and pupae are protected from surface-applied insecticides in fruits and soil. So, there is a pressing need for more eco-friendly and selective control measures with new modes of action. Among such measures are entomopathogenic fungi (EPFs) and nematodes (EPNs). I gathered knowledge on past and present research about EPFs and EPNs as biocontrol agents against fruit flies to investigate approaches that may improve their capacities. I also highlighted several recommendations that may help future field studies on the suppression of fruit fly populations by EPFs and EPNs.     

Host specificity testing and suitability of the parasitoidMicroctonus hyperodae (Hym.: Braconidae,Euphorinae) as a biological control agent ofListronotus bonariensis (Col.: Curculionidae) in New Zealand

The behaviour of the parasitoidMicroctonus hyperodae Loan was studied under quarantine conditions to determine its likely host range in New Zealand. The species was imported from South America as a potential biological control agent of Argentine stem weevil,Listronotus bonariensis (Kuschel). The study involved systematic evaluation of the parasitoid's behaviour when exposed to 24 non-host weevil species; all but three of these were native to New Zealand. Of those tested, four were found to sustain someM. hyperodae development. However, further examination showed that in all but one species,Irenimus aequalis (Broun), parasitoid development was impeded, with up to 50% of the larvae becoming encapsulated. Overall, those weevil species that were attacked produced only 19% of the parasitoids derived fromL. bonariensis controls. As an adjunct to this quarantine study, a review of the habitats of the native weevil and target pest populations indicated that refugia would probably exist for native alpine species. I. aequalis was not considered to be threatened byM. hyperodae as this weevil has benefited from the advent of European agricultural systems to the extent that it is now recognised as a minor pest. In view of its relatively oligophagous behaviour, the parasitoid was recommended as suitable for release.      

Host influences on the pathogenicity of Heterorhabditis megidis

The infectivity of infective juveniles(IJs) of Heterorhabditis megidis (strain NLH-E87.3) produced on small, medium and large larvae ofGalleria mellonella, and on medium and largelarvae of Otiorhynchus sulcatus was tested underlaboratory conditions against G. mellonella andO. sulcatus larvae. Infective juvenilesoriginating from small G. mellonella exposed toan initial dose of one IJ were more infectious thanthose from small cadavers exposed to a dose of 30 IJs.Independent of the initial inoculum size, IJs fromsmall cadavers of G. mellonella were moreinfectious than those from medium and large cadavers.At a dose of one IJ per larva, IJs originating frommedium size O. sulcatus cadavers were moreinfective against G. mellonella than againstO. sulcatus larvae. Large G. mellonellalarvae were less susceptible to all IJ batches thanmedium and small sized larvae.     

Experimental evaluation of the impacts of two ant species on banana weevil in Uganda

The banana weevil, Cosmopolites sordidus (Germar), is an important pest of bananas. Predatory ants are increasingly being viewed as possible biological control agents of this pest because they are capable of entering banana plants and soil in search of prey. We studied ant predation on banana weevil in Uganda in crop residues and live plants in both laboratory and field experiments. Field studies with live plants used chemical ant exclusion in some plots and ant enhancement via colony transfer in others to measure effects of Pheidole sp. 2 and Odontomachus troglodytes Santschi on plant damage and densities of immature banana weevils.In crop residues, an important pest breeding site, twice as many larvae were removed from ant-enhanced plots as in control plots. In young (2 month) potted suckers held in shade houses, ant ability to reduce densities of banana weevil life stages varied with the weevil inoculation rate. At the lowest density (2 female weevils per pot), densities of eggs, larvae, and pupae were reduced by ants. At higher rates there was no effect. In older suckers (5–11 months) grown in larger containers, banana weevil densities were not affected by ants, but damage levels were reduced. In a field trial lasting a full crop cycle (30 months), we found that the ants tested reduced the density of banana weevil eggs in suckers during the crop, but did not affect larval densities in the sampled suckers. However, most larvae occur in the main banana plants, rather than associated suckers. Nevertheless, levels of damage in mature plants at harvest did not differ between Amdro-treated and ant-enhanced plots, suggesting the ant species studied were not able to provide economic control of banana weevil under our test conditions.     

Fecundity, longevity and establishment of Otiorhynchus sulcatus (Fabricius) and Otiorhynchus ovatus (Linnaeus) (Coleoptera: Curculionidae) from the Pacific North-west of the United States of America on selected host plants

1 The fecundity, longevity and establishment of Otiorhynchus sulcatus and Otiorhynchus ovatus from the Pacific North‐west U.S.A. was studied on five selected host plants: Picea abies‘Nidiformis’, Picea glauca‘Conica’, Taxus baccata, Rhododendron catawbiense‘Boursault’ and Fragaria×ananassa‘Totem’. 2 Teneral adults were used to study adult longevity and reproductive success. Leaves of these host plants were used for sustenance for 9 months. Larval establishment was studied by infesting potted host plants with eggs. 3 Fragaria×ananassa‘Totem’ produced the longest survival, shortest preoviposition time, the greatest number of eggs, and the highest fertility for adults of both species. Picea spp. were not good adult hosts for O. sulcatus. Taxus was a good adult host for O. sulcatus, but was a nonhost for adults and larvae of O. ovatus. 4 Adult hosts did not affect preoviposition time or egg viability with O. ovatus adults. With O. sulcatus, preoviposition time was greatly increased and egg viability was < 50% on Picea spp. 5 The best larval host was F.×ananassa‘Totem’ for O. sulcatus and P. glauca‘Conica’ for O. ovatus. Rhododendron was a poor larval host for both species. 6 When all of the studies on these two pests are considered, O. sulcatus appears to have varying host preferences from among its many geographical areas of occurrence whereas O. ovatus has a more universal host selection.