Effects of acclimation and diapause on the cold tolerance of Trogoderma granarium

Khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), is a pest of stored grain in Africa, Asia, and Europe. It is a quarantine insect for much of the rest of the world. Control of T. granarium can be achieved with methyl bromide, but this fumigant is an ozone‐depleting substance and is being phased out worldwide. Thus, there is an urgent need to find new methods of control, including the use of low temperatures. Here, we assess the effects of diapause and cold acclimation on the cold tolerance of T. granarium. The percentage of larvae in diapause increased with larval density, reaching 57.3% when reared at a density of 73 larvae g^?1 diet. The cold tolerance of T. granarium was assessed by the supercooling points (SCPs) of various life stages. The SCP of non‐acclimated insects ranged from ?26.2 ± 0.2 °C (mean ± SEM) for eggs to ?14.4 ± 0.4 °C for larvae. The lowest SCP for larvae, ?24.3 ± 0.3 °C, was obtained for diapausing‐acclimated larvae. Based on mean LT₅₀ values, the most cold‐tolerant stage at ?10 °C was the diapausing‐acclimated larvae (87 days) followed by non‐diapausing‐acclimated larvae (51 days), diapausing non‐acclimated larvae (19 days), adults (4 days), non‐diapausing non‐acclimated larvae (2 days), pupae (0.4 days), and eggs (0.2 days). The estimated times to obtain 99.9968% mortality (Probit 9) for diapausing‐acclimated larvae are 999, 442, 347, 84, and 15 days at 0, ?5, ?10, ?15, and ?20 °C, respectively. Probit 9 is an estimated value used by quarantine experts to estimate conditions that are required to kill all insects. In light of the long exposure time needed to control T. granarium even at ?20 °C, cooling to below ?27 °C (i.e., below the SCP of eggs) will quickly kill all life stages and may be the best way to control this insect with low temperatures.     

Why Callosobruchus rhodesianus causes limited damage during storage of cowpea seeds in a tropical humid zone in Togo

The sympatric bruchids Callosobruchus rhodesianus (Pic) and Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) colonize cultures of cowpea, Vigna unguiculata (Walp.) (Papilionaceae), in Togo at the end of the rainy season. Seeds containing larvae of the two bruchid species were introduced into the storage systems. Callosobruchus rhodesianus adults emerged from the seeds at the beginning of storage, but this species disappeared quickly and C. maculatus became dominant. Analysis of the reproduction of females collected at the beginning of storage made it possible to distinguish between four groups of females differing in their reproductive activity. Three groups were sexually active but they differed in their fecundity and the duration of the latency period before the first oviposition phase. The fourth group of females was in reproductive diapause. In interspecific competition, the presence of C. maculatus larvae reduced the survival chances of C. rhodesianus and therefore is disadvantageous for this species. The main factors explaining the rapid decrease of the C. rhodesianus populations under storage conditions were the variability of female reproductive activity with the emergence of insects in reproductive diapause and the significant larval mortality in interspecific competition with C. maculatus.     

Etude olfactométrique de l'action de diverses substances allélochimiques végétales dans la recherche de l'hote par Diadromus pulchellus (Hymenoptera,Ichneumonidae)

Résumé La recherche de l'habitat d'un hôte potentiel par D. pulchellus, endoparasite considéré comme spécialiste des nymphes d'A. assectella, est abordée chez les adultes femelles et mâles, en olfactométrie, par l'étude de leur comportement locomoteur. L'activité locomotrice et l'attraction sont ainsi analysées en présence de substances allélochimiques issues ou non de végétaux pouvant abriter un hôte. Que les composés soufrés testés soient stables ou non, ils ne déclenchent pas d'attraction chez les hyménoptères quel que soit leur sexe et le type d'olfactomètre utilisé, contrairement aux imagos du phytophage-hôte, A. assectella, attirés par les composés soufrés instables spécifiques du poireau. L'activité locomotrice des hyménoptères des deux sexes est stimulée par divers composés volatils soufrés de synthèse ou émis naturellement par les Crucifères et par les Allium consommés par les larves d'A. assectella. Les substances efficaces sont généralément stables et sont caractérisées par le groupement actif R-S-, à condition que R ne soit pas un allyle. Par ailleurs, des composés volatils non soufrés contenus dans des végétaux autres que les Allium et les Crucifères ne stimulent pas le comportement locomoteur des hyménoptères. Ces différentes observations permettent d'envisager que D. pulchellus est un spécialiste inféodé à des microlépidoptères s'alimentant sur des végétaux soufrés et non sur les seuls Allium.

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Summary Searching the host habitat by the endoparasite wasp Diadromus pulchellus, considered to be a specialist of Acrolepiopsis assectella nymphs, is studied in females and males by analysis of locomotory behaviour in olfactometers. Thus, locomotor activity and attraction are studied in the presence or absence of air-borne volatiles emitted by plants able to shelter a potential host-moth. Stable and unstable sulphur compounds used do not release attraction in female and male ichneumonids whatever the type of olfactometer used. By contrast, phytophagous host adults are attracted by unstable specific sulphur compounds of the leek. Locomotor activities of D. pulchellus females and males are stimulated by various volatile sulphur compounds of synthetic origin or naturally occurring in Allium eaten by A. assectella larvae and in Crucifera. The effective compounds generally are stable and characterized by the active group R-S — in which the alkyl moiety must not be an allyl one. On the other hand, volatiles without sulphur, emitted by plants which do not belong to Cruciferae or Allium, do not stimulate the hymenopteran locomotor activity. These observations suggest that D. pulchellus is oligophagous, attracted to microlepidoptera developing on plants containing sulphur compounds and not only on Allium.

     

Role of Caterpillar Silk Thread in Location of Host Pupae by the Parasitoid <Emphasis Type="Italic">Diadromus pulchellus</Emphasis>

Diadromus pulchellus is a solitary ichneumonid parasitoid. Its only known host is the pupa of Acrolepiopsis assectella, a specialist herbivore of Allium species. D. pulchellus females parasitize A. assectella pupae within 48 h after the caterpillars spin their cocoon and begin to pupate. Having observed that the cocoon produced by the leek moth caterpillar stimulates parasitoid egg-laying and that caterpillar leaves a silk thread, we studied the hypothesis that silk thread might be involved in host-finding by the parasitoid. Behavioral tests showed that when D. pulchellus females encounter a host silk thread, they change directions, follow the thread, and quickly locate the host. These findings show that pupal parasitoids can use signals produced by their hosts at the developmental instar preceding the one that they parasitize.     

Insecticidal action of Bauhinia monandra leaf lectin (BmoLL) against Anagasta kuehniella (Lepidoptera: Pyralidae), Zabrotes subfasciatus and Callosobruchus maculatus (Coleoptera: Bruchidae)

Bruchid beetle larvae cause major losses in grain legume crops throughout the world. Some bruchid species, such as the cowpea weevil (Callosobruchus maculatus) and the Mexican bean weevil (Zabrotes subfasciatus), are pests that damage stored seeds. The Mediterranean flour moth (Anagasta kuehniella) is of major economic importance as a flour and grain feeder; it is often a severe pest in flour mills. Plant lectins have been implicated as antibiosis factors against insects. Bauhinia monandra leaf lectin (BmoLL) was tested for anti-insect activity against C. maculatus, Z. subfasciatus and A. kuehniella larvae. BmoLL produced ca. 50% mortality to Z. subfaciatus and C. maculatus when incorporated into an artificial diet at a level of 0.5% and 0.3% (w/w), respectively. BmooLL up to 1% did not significantly decrease the survival of A. kuehniella larvae, but produced a decrease of 40% in weight. Affinity chromatography showed that BmoLL bound to midgut proteins of the insect C. maculatus. 33 kDa subunit BmoLL was not digested by midgut preparations of these bruchids. BmoLL-fed C. maculatus larvae increased the digestion of potato starch by 25% compared with the control. The transformation of the genes coding for this lectin could be useful in the development of insect resistance in important agricultural crops.     

Feeding responses of specialist herbivores to plant extracts and pure allelochemicals: effects of prolonged exposure

We investigated the possibility of decreased feeding deterrent response following prolonged exposure in three specialist herbivores, Plutella xylostella (larvae), Pseudaletia unipuncta (larvae), and Epilachna varivestis (adults) through leaf disc choice and no‐choice tests. Neonate larvae (<24 h old) of the three species were reared on their host plants sprayed with the antifeedants until tested. Our results demonstrated that Ps. unipuncta did not show a decrease in feeding deterrent response to extracts of Melia volkensii (choice and no‐choice tests) or oregano (Origanum vulgare) (choice test) following prolonged exposure. Plutella xylostella exhibited a decrease in feeding deterrent response to M. volkensii in a choice test only, but not to oregano. Although not significant, we did find a trend toward decreasing feeding deterrent response to M. volkensii by both species in no‐choice tests. However, both species exhibited a significant decrease in feeding deterrent response to pure allelochemicals (Ps. unipuncta to thymol, and P. xylostella to thymol and toosendanin) compared with the naïve groups, following prolonged exposure in leaf disc choice tests. Epilachna varivestis showed a significant decrease in feeding deterrent responses to both oregano and thymol in leaf disc choice tests. We conclude from our present and previous studies that not only are there interspecific differences between generalist and specialist species but also among specialist species.     

Phenology and temperature‐dependent development of Ceutorhynchus assimilis,a potential biological control agent for Lepidium draba

Lepidium draba (Brassicaceae) is a major concern for agriculture and biodiversity in the western United States. As current control methods do not provide long‐term, sustainable solutions, research has been conducted to find biological control agents. Ceutorhynchus assimilis is one of the currently investigated candidates. Known as oligophagous in the literature, a specialist clade of this root‐galling weevil exists in southern Europe. This raised the question of its ability to survive in colder climates in the target range. We investigated the phenology of C. assimilis in the field in southern France (specialist clade) and Romania (generalist clade) and measured various temperature‐dependent parameters in the laboratory. In both ranges, weevils were univoltine. Oviposition in autumn started later in France compared to Romania, while mature larvae exited galls (to pupate in the soil) earlier the following year. On average, 25% and 32% of galls from France and Romania were completely below the soil surface, respectively, and this appeared to depend on soil substrate. Weevils transported from France to Romania were able to develop, but at a much lower rate than Romanian weevils. Mortality of overwintering larvae of both clades increased with decreasing temperature and exposure time. At ?5°C, lethal times Lt₅₀ and Lt₉₅ were 15 and 42 days for the specialist clade and 26 and 72 days for the generalist clade. A higher proportion of third instar larvae compared to first and second instar larvae survived. Pupation time at different temperatures did not differ between weevils from France or Romania. A climate match model (comparing winter temperatures) indicated that the specialist clade of C. assimilis from France has the potential to establish in some parts of the target range (e.g. Washington, Oregon, California). However, temperature extremes and winters without snow cover will likely limit its establishment unless rapid adaptive evolution takes place.     

Activity of glutathione S‐transferase and esterase enzymes in Helicoverpa armigera (Hübner) after exposure to entomopathogenic fungi

Helicoverpa armigera, a polyphagous insect of crops and vegetables, is acquiring resistance against many commercial insecticides. The present study shows variations in the activity of two detoxification enzymes, namely esterase and glutathione S‐transferase (GST), in H. armigera after exposure to different isolates of entomopathogenic fungi. After treatment of larvae with the different isolates (Day 0), samples were collected on three days (Days 3, 5 and 7) for enzyme analysis. High GST activity was found in samples of hemolymph, intestine and fat bodies of H. armigera following treatment with Beauveria bassiana (isolate Bb‐08), Metarhizium anisopliae (isolates Ma‐11.1 and Ma‐4.1), and Isaria fumosorosea (isolates If‐02 and If‐2.3). High esterase activity was recorded in samples of the intestine and fat bodies on various days after treatment, whereas increased esterase activity in hemolymph was noted only in samples from Day 5 after treatment with M. anisopliae (Ma‐4.1). The detection of high GST and esterase activity demonstrates the possibility of the development of resistance against these microbial control agents in H. armigera.     

Behavioural responses to dimethyl disulphide by Aleochara bilineata and Aleochara bipustulata

Adult Aleochara bipustulata L. and Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) are predatory on immature stages of cabbage root fly Delia radicum (L.) (Diptera: Anthomyiidae). Larvae of the two Aleochara are parasitoids of D. radicum pupae. Female Aleochara lay eggs near D. radicum puparia; the newly‐hatched Aleochara larvae enter puparia and consume the contents. Delia radicum‐infested roots of brassicas give off dimethyl disulphide (DMDS). In the field, DMDS attracts adult Aleochara to pitfall traps but does not enhance the biological control of D. radicum. In the present study, we investigate the behavioural responses of the Aleochara to DMDS in still air, as well as in moving air in a Y‐tube olfactometer, and also investigate the influence of DMDS on host selection. In larvae of both Aleochara species, DMDS induces a restricted‐area search in still air, resulting in elevated frequencies of attack of D. radicum puparia close to a source of DMDS. In the olfactometer, newly‐emerged virgin adults of both sexes of both Aleochara species choose alternatives to DMDS, older recently‐mated females are attracted to DMDS, and older males and older mate‐deprived females show no preference. Mating status of males determines the switch of their response to DMDS from avoidance to indifference. We conclude that DMDS is an important cue for host‐finding, although other cues are involved in mate‐finding. We discuss the implications for use of DMDS to enhance D. radicum mortality and for parasitism of nontarget species if A. bipustulata is introduced to Canada for biological control of D. radicum.     

Pre- and post-imaginal experience in a specialist parasitoidDiadromus pulchellus (Hym.: Ichneumonidae)

The locomotory behaviour of femaleDiadromus pulchellus Wesm. (Ichneumonidae), a specialist endoparasitoid ofAcrolepiopsis assectella Zell. chrysalids, was analyzed in an olfactometer. Three parameters were measured: distance walked, number of turns and female distribution. The volatiles emitted by the larval frass ofA. assectella which feeds exclusively onAllium plants modified all three parameters. When females were placed in contact with frass and/or with the host before the olfactometer test, the number of turns was lower in comparison to that of naive females tested without prior contact with the host and/or its frass. This indicated that the trajectory of experienced females towards the odour source was more direct. Associative learning is a possible mechanism behind this change. No evidence of pre-imaginal experience was found because parasitoids emerging from the chrysalids of a non-host moth,P. interpunctella, responded to the frass volatiles of the usual host,A. assectella, in the same way as parasitoids reared on this latter host.     

Comparative assessment of the thermal tolerance of spotted stemborer,Chilo partellus (Lepidoptera: Crambidae) and its larval parasitoid,Cotesia sesamiae (Hymenoptera: Braconidae)

Under stressful thermal environments, insects adjust their behavior and physiology to maintain key life‐history activities and improve survival. For interacting species, mutual or antagonistic, thermal stress may affect the participants in differing ways, which may then affect the outcome of the ecological relationship. In agroecosystems, this may be the fate of relationships between insect pests and their antagonistic parasitoids under acute and chronic thermal variability. Against this background, we investigated the thermal tolerance of different developmental stages of Chilo partellus Swinhoe (Lepidoptera: Crambidae) and its larval parasitoid, Cotesia sesamiae Cameron (Hymenoptera: Braconidae) using both dynamic and static protocols. When exposed for 2 h to a static temperature, lower lethal temperatures ranged from ?9 to 6 °C, ?14 to ?2 °C, and ?1 to 4 °C while upper lethal temperatures ranged from 37 to 48 °C, 41 to 49 °C, and 36 to 39 °C for C. partellus eggs, larvae, and C. sesamiae adults, respectively. Faster heating rates improved critical thermal maxima (CT_max) in C. partellus larvae and adult C. partellus and C. sesamiae. Lower cooling rates improved critical thermal minima (CT_min) in C. partellus and C. sesamiae adults while compromising CT_min in C. partellus larvae. The mean supercooling points (SCPs) for C. partellus larvae, pupae, and adults were ?11.82 ± 1.78, ?10.43 ± 1.73 and ?15.75 ± 2.47, respectively. Heat knock‐down time (HKDT) and chill‐coma recovery time (CCRT) varied significantly between C. partellus larvae and adults. Larvae had higher HKDT than adults, while the latter recovered significantly faster following chill‐coma. Current results suggest developmental stage differences in C. partellus thermal tolerance (with respect to lethal temperatures and critical thermal limits) and a compromised temperature tolerance of parasitoid C. sesamiae relative to its host, suggesting potential asynchrony between host–parasitoid population phenology and consequently biocontrol efficacy under global change. These results have broad implications to biological pest management insect–natural enemy interactions under rapidly changing thermal environments.     

Aerosol distribution and efficacy in a commercial food warehouse

A series of field trials were conducted in a commercial food storage facility to evaluate exposure of stored‐product insects to aerosol formulations of synergized pyrethrins and the insect growth regulator methoprene. When adults of Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (Jacqueline DuVal), the confused flour beetle were exposed with and without a food source to synergized pyrethrin aerosol, there was no difference in adult mortality with respect to availability of food at either 7 or 14 days after exposure (P≥ 0.05). However, mortality was lower in T. confusum (40.4% and 79.3% with flour at 7 and 14 days, 38.9% and 84.8% without flour at 7 and 14 days) compared to T. castaneum (96.5% and 99.8% with flour at 7 and 14 days, 91.0% and 98.7% without flour at 7 and 14 days). Few late‐stage larvae and pupae of either species exposed to the pyrethrin aerosol emerged as adults. In tests with methoprene aerosol, adult emergence of exposed 3‐and 4‐week‐old larvae of T. confusum was less than 2%. Only 0.3% of 4‐week‐old larvae of T. castaneum exposed in open and obstructed areas emerged as adults. Emergence of adults from eggs of Plodia interpunctella (Hübner), the Indianmeal moth, embedded in culture media and exposed to the methoprene aerosol was 13.2%± 3.5%. Results show that the aerosols evaluated in our study could give effective control of some of the major stored‐product insect pests in commercial food storage facilities, and may offer an alternative to fumigation.     

Effects of herbicide-tolerant transgenic oilseed rape genotypes on honey bees and other pollinating insects under field condtions

Abstract Various parameters of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), such as ovipositional behaviour, development period, and ability of newly hatched larvae to utilise the host for further growth, are affected by host attributes that could be physical or chemical in nature. These factors were assessed using green‐ and black‐gram (Leguminosae) seed characteristics to explore whether they affected oviposition behaviour, fecundity, and breeding success in C. maculatus, and to determine whether the presence of cysteine proteinase inhibitor (CPI) within the seeds caused inhibition of proteinase activity in C. maculatus. Investigation revealed that green‐gram (Vigna radiata (L.) Wilczek) varieties differed from black‐gram (Vigna mungo (L.) Hepper) varieties by having softer seeds with smoother seed coats. Green‐gram NM92 and the control had the heaviest seeds with the largest surface area and medium hardness, black‐gram had seeds with medium weight, medium surface area, and maximum hardness, and green‐gram NCM209 had the lightest seeds with smallest surface area and minimum hardness. Varieties with smooth seed coats and greater seed weight and surface area were preferred for oviposition. Grain texture was more important as an oviposition stimulus than grain surface area and size for the Islamabad biotype of C. maculatus. The level of CPI in seeds was not, on its own, responsible for the observed differences in insect development period or larval activity. Development period was shorter in green‐gram with softer seeds and was prolonged in black‐gram with harder seeds. Although C. maculatus did not suffer higher mortality in black‐gram seeds, the delay in development alone may lead to a considerable reduction in seed loss during storage, due to the low rate of multiplication and lower population growth.     

Transcriptional profile and differential fitness in a specialist milkweed insect across host plants varying in toxicity

Interactions between plants and herbivorous insects have been models for theories of specialization and co‐evolution for over a century. Phytochemicals govern many aspects of these interactions and have fostered the evolution of adaptations by insects to tolerate or even specialize on plant defensive chemistry. While genomic approaches are providing new insights into the genes and mechanisms insect specialists employ to tolerate plant secondary metabolites, open questions remain about the evolution and conservation of insect counterdefences, how insects respond to the diversity defences mounted by their host plants, and the costs and benefits of resistance and tolerance to plant defences in natural ecological communities. Using a milkweed‐specialist aphid (Aphis nerii) model, we test the effects of host plant species with increased toxicity, likely driven primarily by increased secondary metabolites, on aphid life history traits and whole‐body gene expression. We show that more toxic plant species have a negative effect on aphid development and lifetime fecundity. When feeding on more toxic host plants with higher levels of secondary metabolites, aphids regulate a narrow, targeted set of genes, including those involved in canonical detoxification processes (e.g., cytochrome P450s, hydrolases, UDP‐glucuronosyltransferases and ABC transporters). These results indicate that A. nerii marshal a variety of metabolic detoxification mechanisms to circumvent milkweed toxicity and facilitate host plant specialization, yet, despite these detoxification mechanisms, aphids experience reduced fitness when feeding on more toxic host plants. Disentangling how specialist insects respond to challenging host plants is a pivotal step in understanding the evolution of specialized diet breadths.     

Analyse,dans deux types d'olfactomètres,du comportement de quête des femelles deDiadromus pulchellus en présence d'odeurs du phytophage-hôte et du végétal attaqué ou non

Résumé Le comportement de quête des femelles deDiadromus pulchellus Wesmael ou comportement locomoteur impliqué dans la recherche des chrysalides de l'h?teAcrolepiopsis assectella Zeller, lépidoptère inféodé auxAllium L., est étudié en présence de différentes odeurs issues des chrysalides-h?tes, du poireau consommé par les larves du phytophage et de certains allélochimiques soufrés volatils desAllium. Les deux composantes de ce comportement, la locomotion et l'attraction, sont analysées à deux vitesses d'air différentes dans deux types d'olfactomètres tubulaires, l'un à flux d'air continu et l'autre, plus grand, avec des jets d'air alternativement purs et odorants. La locomotion des femelles est analogue avec ou sans flux d'air. Quel que soit l'olfactomètre et la vitesse d'air utilisée, cette activité est stimulée quand l'air véhicule l'odeur des limbes attaqués et/ou des fécès larvaires. Il en est de même avec deux allélochimiques soufrés testés, les disulfure et thiosulfonate de dipropyle, et avec l'acétate d'éthyle présent aussi dans lesAllium. Par ailleurs, l'odeur des larves de dernier stade accro?t la locomotion des femelles alors que celle des jeunes nymphes est sans effet quel que soit l'olfactomètre utilisé. L'attraction ne se manifeste que si le flux d'air est présenté soit par jets brefs alternativement pur et odorant, soit en continu mais une vitesse minimale est alors nécessaire. Dans ces conditions une chémoanémotaxie appara?t chez les femelles seulement avec l'odeur du poireau attaqué et avec les allélochimiques soufrés desAllium. Particulièrement, le thiosulfinate de dipropyle aurait un r?le primordial dans la réponse chémoanémotactique du parasito?de, comme cela a déjà été montré chez les adultes du phytophage-h?te. Une anémotaxie existe également chez les femelles. Elle est d'autant plus marquée que la vitesse du flux d'air pur est élevée. Le r?le de celle-ci dans le comportement de quête ainsi que celui de la chémoanémotaxie et de la stimulation de la locomotion par les odeurs liées au végétal consommé par l'h?te est discuté.

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Summary The behaviour of females of the entomophagous waspDiadromus pulchellus Wesmael, during their search for larvae of the mothAcrolepiopsis assectella Zeller, a specialist feeder onAllium L. species, was studied. Parasitoid movement and attraction were observed at 2 different air speeds in 2 tubular olfactometers. Air flow was continuous in the smaller olfactometer but was presented as pulsed puffs of clean and then odorous air in the larger olfactometer. The odours from damagedAllium plants, from the feedingAcrolepiopsis larvae, and from certain volatile sulphur chemicals present inAllium species were tested.Diadromus movement was similar in still or moving clean air, but increased when the air flow contained odours from leaves with or without larval frass, from feeding larvae and from ethyl acetate, dipropyl disulfide and propyl propane thiosulfonate. Young larvae within cocoons did not increase parasitoid locomotion. A chemoanemotaxis was observed only when the odours were presented in moving air. Female attraction occurred only to the odours from damaged leeks, dipropyl disulfide, propyl propane thiosulfonate and propyl propane thiosulfinate. This last chemical is also the most important in initiating chemoanemotaxis by adultA. assectella. The roles of kineses, anemotaxis and chemoanemotaxis are discussed in the search behaviour ofDiadromus.

     

Engineering of benzylglucosinolate in tobacco provides proof-of-concept for dead-end trap crops genetically modified to attract Plutella xylostella (diamondback moth)

Glucosinolates are biologically active natural products characteristic of crucifers, including oilseed rape, cabbage vegetables and the model plant Arabidopsis thaliana. Crucifer‐specialist insect herbivores, like the economically important pest Plutella xylostella (diamondback moth), frequently use glucosinolates as oviposition stimuli. This suggests that the transfer of a glucosinolate biosynthetic pathway to a non‐crucifer would stimulate oviposition on an otherwise non‐attractive plant. Here, we demonstrate that stable genetic transfer of the six‐step benzylglucosinolate pathway from A. thaliana to Nicotiana tabacum (tobacco) results in the production of benzylglucosinolate without causing morphological alterations. Benzylglucosinolate‐producing tobacco plants were more attractive for oviposition by female P. xylostella moths than wild‐type tobacco plants. As newly hatched P. xylostella larvae were unable to survive on tobacco, these results represent a proof‐of‐concept strategy for rendering non‐host plants attractive for oviposition by specialist herbivores with the long‐term goal of generating efficient dead‐end trap crops for agriculturally important pests.     

Effects of chlorpyrifos on enzymatic systems of Cydia pomonella (Lepidoptera: Tortricidae) adults

The control program of codling moth (Cydia pomonella L.) in the Río Negro and Neuquén Valley is intended to neonate larvae. However, adults may be subjected to sublethal pesticide concentrations generating stress which might enhance both mutation rates and activity of the detoxification system. This study assessed the exposure effects of chlorpyrifos on target enzyme and, both detoxifying and antioxidant systems of surviving adults from both a laboratory susceptible strain (LSS) and a field population (FP). The results showed that the FP was as susceptible to chlorpyrifos as the LSS and, both exhibited a similar chlorpyrifos‐inhibitory concentration 50 (IC₅₀) of acetylcholinesterase (AChE). The FP displayed higher carboxylesterase (CarE) and 7‐ethoxycoumarine O‐deethylase (ECOD) activities than LSS. Both LSS and FP showed an increase on CarE activity after the exposure to low‐chlorpyrifos concentrations, followed by enzyme inhibition at higher concentrations. There were no significant differences neither in the activities of glutathione S‐transferases (GST), catalase (CAT) and superoxide dismutase (SOD) nor in the reduced glutathione (GSH) content between LSS and FP. Moreover, these enzymes were unaffected by chlorpyrifos. In conclusion, control adults from the FP exhibited higher CarE and ECOD activities than control adults from the LSS. AChE and CarE activities were the most affected by chlorpyrifos. Control strategies used for C. pomonella, such as rotations of insecticides with different modes of action, will probably delay the evolution of insecticide resistance in FPs from the study area.     

Resistance to the rice leaf bug, Trigonotylus caelestialium, is conferred by Neotyphodium endophyte infection of perennial ryegrass, Lolium perenne

Neotyphodium fungal endophytes form mutualistic symbiotic associations with many grasses of the subfamily Pooideae, including important forage and turfgrass species. This relationship provides a competitive advantage to the host plant by increasing abiotic/biotic stress tolerance, such as its resistance to drought, diseases, and insect pests. The insect deterrent effects of endophytes are now receiving attention in Japan, as insect pests growing in meadows are causing problems in adjacent rice paddies. One of the most serious problems is the kernel spotting of rice grains caused by the rice leaf bug, Trigonotylus caelestialium Kirkaldy (Heteroptera: Miridae), which reproduces on Lolium species grown as forage. To determine the potential of Neotyphodium endophytes to reduce the invasion of rice crops by T. caelestialium from adjacent Lolium crops, we carried out choice and no‐choice feeding tests using endophyte‐infected and endophyte‐free clonal perennial ryegrass (Lolium perenne L.) (Poaceae). Our experiments revealed that the presence of the Neotyphodium endophyte strongly deterred the feeding of both first‐instar larvae and adults of T. caelestialium. These results show the potential of Neotyphodium endophytes to reduce the number of T. caelestialium in forage fields and grasslands, and thus to reduce the damage to rice grains caused by this insect pest.     

Synergistic activity of Bacillus thuringiensis δ‐endotoxin and TMOF against Culex pipiens and Spodoptera littoralis larvae

Trypsin Modulating Oostatic Factor (TMOF) is a decapeptide hormone that inhibits the biosynthesis of digestive enzymes in the mosquito midgut. The hormone inhibits food digestion and ultimately leads to starvation and death. It has been used as a biological insecticide to control mosquitoes. In an attempt to increase the insecticidal activity of TMOF, a combination of CryIC (δ‐endotoxin from Bacillus thuringiensis) and TMOF was determined. Eight recombinant proteins fused with GST (glutathione‐S‐transferase) were expressed in Escherichia coli cells. Their insecticidal activities were determined against Culex pipiens and Spodoptera littoralis larvae. Purified GST‐TMOF and its analogue GST‐YDPAS exhibited a moderate toxicity on C. pipiens larvae with LC₅₀ of 145.9 and 339.9 μg/mL, respectively. Unexpectedly, no mortality was observed in first instar larvae of S. littoralis. Puirified GST‐TMOF and GST‐YDPAS together with Bt toxin showed a synergistic toxic effect on both Culex and Spodoptera larvae. In the presence of 100 μg/mL GST‐TMOF and GST‐YDPAS, the median lethal concentration of entomocidus on culex larvae decreased from 52.1 to 16.7 and 31.9 μg/mL, respectively. Likewise, GST‐TMOF and GST‐YDPAS incorporated with 0.07 μg/cm² of enotmocidus showed insecticidal activity against S. littoralis with LC₅₀ of 16.4 and 21.9 μg/cm². The E. coli lysates containing GST‐CryIC and its 3′‐truncated version showed low toxicity against the lepidopteran insect (10.8 and 16.6 μg/cm²) compared to 0.15 μg/cm² of the native crystalline form of CryIC. Similarly, the mosquitocidal activity of the recombinant Bt toxins was low.     

Aversion and attraction to harmful plant secondary compounds jointly shape the foraging ecology of a specialist herbivore

Most herbivorous insect species are restricted to a narrow taxonomic range of host plant species. Herbivore species that feed on mustard plants and their relatives in the Brassicales have evolved highly efficient detoxification mechanisms that actually prevent toxic mustard oils from forming in the bodies of the animals. However, these mechanisms likely were not present during the initial stages of specialization on mustard plants ~100 million years ago. The herbivorous fly Scaptomyza nigrita (Drosophilidae) is a specialist on a single mustard species, bittercress (Cardamine cordifolia; Brassicaceae) and is in a fly lineage that evolved to feed on mustards only in the past 10–20 million years. In contrast to many mustard specialists, S. nigrita does not prevent formation of toxic breakdown products (mustard oils) arising from glucosinolates (GLS), the primary defensive compounds in mustard plants. Therefore, it is an appealing model for dissecting the early stages of host specialization. Because mustard oils actually form in the bodies of S. nigrita, we hypothesized that in lieu of a specialized detoxification mechanism, S. nigrita may mitigate exposure to high GLS levels within plant tissues using behavioral avoidance. Here, we report that jasmonic acid (JA) treatment increased GLS biosynthesis in bittercress, repelled adult female flies, and reduced larval growth. S. nigrita larval damage also induced foliar GLS, especially in apical leaves, which correspondingly displayed the least S. nigrita damage in controlled feeding trials and field surveys. Paradoxically, flies preferred to feed and oviposit on GLS‐producing Arabidopsis thaliana despite larvae performing worse in these plants versus non‐GLS‐producing mutants. GLS may be feeding cues for S. nigrita despite their deterrent and defensive properties, which underscores the diverse relationship a mustard specialist has with its host when lacking a specialized means of mustard oil detoxification.