Oviposition Stimulants Research Articles

Evaluating the Effects of Flavonoids on Insects: Implications for Managing Pests Without Harming Beneficials

Flavonoids have multiple functions, including host-plant defense against attacks from herbivorous insects. This manuscript reviewed and analyzed the scientific literature to test the hypothesis that flavonoids can be utilized to manage pests without causing significant harm to beneficials. The methodology involved using recognized literature databases, e.g., Web of Science, Scopus, and CAB Abstracts, via the USDA-ARS, National Agricultural Library, DigiTop literature retrieval system. Data were compiled in tables and subjected to statistical analysis, when appropriate. Flavonoids were generally harmful to true bugs and true flies but harmless to honey bees. Flavonoid glycosides showed a tendency to harm true bugs (Heteroptera) and true flies (Diptera). Flavonoid glycosides were harmless to sawflies. Flavonoids and flavonoid glycosides produced a mixture of harmful and harmless outcomes to herbivorous beetles, depending on the species. Flavonoid glycosides were harmless to butterflies. In conclusion, specific flavonoids could function as feeding stimulants or deterrents, oviposition stimulants or deterrents, chemical protectants from pesticides, mating attractants, less-toxic insecticides, and other functions. Flavonoids could manage some insect pests without causing significant harm to beneficials (e.g., honey bees). Flavonoid-based insecticides could serve as environmentally benign alternatives to broad-spectrum insecticides against some pests, but field testing is necessary.

Odorant Receptor BdorOR49b Mediates Oviposition and Attraction Behavior of Bactrocera dorsalis to Benzothiazole.

The ability to recognize a host plant is crucial for insects to meet their nutritional needs and locate suitable sites for laying eggs. Bactrocera dorsalis is a highly destructive pest in fruit crops. Benzothiazole has been found to induce oviposition behavior in the gravid B. dorsalis. However, the ecological roles and the olfactory receptor responsible for benzothiazole are not yet fully understood. In this study, we found that adults were attracted to benzothiazole, which was an effective oviposition stimulant. In vitro experiments showed that BdorOR49b was narrowly tuned to benzothiazole. The electroantennogram results showed that knocking out BdorOR49b significantly reduced the antennal electrophysiological response to benzothiazole. Compared with wild-type flies, the attractiveness of benzothiazole to BdorOR49b knockout adult was significantly attenuated, and mutant females exhibited a severe decrease in oviposition behavior. Altogether, our work provides valuable insights into chemical communications and potential strategies for the control of this pest.

Ovipositional responses of tortricid moths to sugars, salts and neem oil

Oviposition is essential in the life history of insects and is mainly mediated by chemical and tactile cues present on the plant surface. Oviposition deterrents or stimulants can modify insect oviposition and be employed in pest control. Relatively few gustatory oviposition stimuli have been described for tortricid moths. In this study the effect of NaCl, KCl, sucrose, fructose and neem oil on the number of eggs laid by Cydia pomonella (L.), Grapholita molesta (Busck) and Lobesia botrana (Dennis & Schifermüller) was tested in laboratory arenas containing filter papers loaded with 3 doses of a given stimulus and solvent control. In general, salts increased oviposition at the mid dose (102 M) and sugars reduced it at the highest dose (103 mM), but these effects depended on the species. Neem oil dramatically reduced the number of eggs laid as the dose increased, but the lowest neem oil dose (0.1% v/v) increased L. botrana oviposition relative to solvent control. Our study shows that ubiquitous plant chemicals modify tortricid moth oviposition under laboratory conditions, and that neem oil is a strong oviposition deterrent. The oviposition arena developed in this study is a convenient tool to test the effect of tastants on the oviposition behavior of tortricid moths.

Abiotic characteristics and organic constituents of oviposition sites as oviposition attractants and stimulants for gravid female stable flies, Stomoxys calcitrans

AbstractGravid female stable flies, Stomoxys calcitrans (L.) (Diptera: Muscidae), oviposit in many types of organic substrates, including animal feces, but there is limited information as to which factors mediate attraction and oviposition. Here, we (1) tested effects of oviposition site moisture and odor on attraction and oviposition by flies, and (2) selected a highly effective oviposition site (fly rearing medium) to determine the key constituent(s) that mediate(s) attraction and oviposition. In moving‐ and still‐air olfactometers as well as large laboratory rooms, we show that (1) odor and moisture of oviposition sites play distinguishable functional roles in the close‐range attraction of gravid female flies and their propensity to oviposit, (2) rearing medium containing fish food, wheat bran, wood chips, and a watery solution of ammonium bicarbonate [(NH4)HCO₃, releasing NH3 and CO2] is a more appealing oviposition site to female flies than is cow feces, (3) ammonium bicarbonate in this medium is the key constituent for stable fly attraction and oviposition, (4) NH3 alone or in combination with CO2, but not CO2 alone, attracts stable flies and induces oviposition, and (5) NH3/CO2 and fish food in combination are more attractive than NH3/CO2 or fish food alone. With fecal bacteria reportedly emitting NH3, and with stable fly larval development reportedly reliant on (fecal) microbes, it follows that gravid female flies may be guided by airborne microbe‐derived cues originating from prospective oviposition sites. Isolating these microbes and identifying their odorants could enable the development of a synthetic odor blend which, coupled with NH3 and CO2, may prove highly effective as a trap lure to capture gravid female stable flies.

Epicuticular wax chemicals of Lablab purpureus subsp. bengalensis influence short-range attraction and oviposition responses in Aphis craccivora and Aphis gossypii.

Lablab purpureus subsp. bengalensis (Jacq.) Verdc. is an important legume of India and Africa. Both aphids, Aphis craccivora Koch and A. gossypii Glover (Hemiptera: Aphididae), are important herbivorous pests of this legume crop. These viviparous females lay nymphs on the leaf surface of this legume plant. Therefore, it is of considerable interest to study whether leaf surface wax chemicals (long-chain alkanes and free fatty acids) of this legume plant served as short-range attractants and oviposition stimulants in both females to lay nymphs. Twenty-one n-alkanes from n-C12 to n-C35 and 11 free fatty acids from C12:0 to C22:0 were identified in leaf surface waxes. Nonacosane and nonadecanoic acid were the most abundant among n-alkanes and free fatty acids, respectively. Both females were attracted towards one leaf equivalent surface wax against the control solvent (petroleum ether) in short Y-tube olfactometer bioassays. A synthetic blend of tetradecane, pentadecane, tetracosane, tridecanoic acid, tetradecanoic acid, and heneicosanoic acid comparable to one leaf equivalent surface wax served as short-range attractants and oviposition stimulants in A. craccivora; whereas a synthetic blend of tetradecane, hexadecane, docosane, nonadecanoic acid, and arachidic acid comparable to one leaf equivalent surface wax acted as short-range attractants and oviposition stimulants in A. gossypii. These results can provide the basis for efficient pest management strategies of A. craccivora and A. gossypii against L. purpureus subsp. bengalensis using host plant leaf surface wax compounds. Further, SEM studies of antennae and forelegs of both aphids were conducted to observe sensilla structures, which help in chemoreception.

A green leaf volatile, (Z)-3-hexenyl-acetate, mediates differential oviposition by Spodoptera frugiperda on maize and rice

BackgroundInsects rely on chemosensory perception, mainly olfaction, for the location of mates, food sources, and oviposition sites. Plant-released volatile compounds guide herbivorous insects to search for and locate their host plants, further helping them to identify suitable positions for oviposition. The fall armyworm Spodoptera frugiperda (S. frugiperda) was found to invade China in 2019 and has since seriously threatened multiple crops, particularly maize and rice. However, the chemical and molecular mechanisms underlying oviposition preference in this pest are not fully understood. Here, the oviposition preference of S. frugiperda on maize and rice plants was investigated.ResultsGC-EAD and GC–MS/MS techniques were used to identify the antennally active volatiles from maize and rice plants. The attraction and oviposition stimulation of identified components to female adults were tested in both laboratory and field settings. The odorant receptors (ORs) on female antennae were expressed in Xenopus oocytes, and their functions evaluated by RNAi. Ten and eleven compounds of maize and rice plants, respectively, were identified to possess electrophysiological activity from headspace volatiles. Among these compounds, (Z)-3-hexenyl-acetate specifically presented in maize volatiles was found to play a critical role in attracting females and stimulating oviposition compared to rice volatiles. Among the cloned ORs on the antennae of both sexes, SfruOR23 with highly female-biased expression mediated the responses of females to (Z)-3-hexenyl-acetate. Knockdown of SfruOR23 using RNAi markedly reduced the electrophysiological response of female antennae and oviposition preference to the compound.Conclusions(Z)-3-Hexenyl-acetate is a key volatile mediating the host and oviposition preference of S. frugiperda on maize. The olfactory receptor of (Z)-3-hexenyl-acetate was identified to be SfruOR23, which is mainly expressed in the antennae of S. frugiperda.

Identification of volatile compounds from fruits aroma and citrus essential oils and their effect on oviposition of Ceratitis capitata (Diptera: Tephritidae).

Ceratitis capitata (Wiedemann), also known as the Mediterranean fruit fly, is one of the most serious pests for several fresh fruit commodities causing extensive fruit losses worldwide. The response of C. capitata adults to fruit and nonfruit volatiles has been extensively studied. However, the linkage between fruit volatiles and the female ovipositional choice has not been fully elucidated. The present study focused on identifying the volatile organic compounds emitted by detached intact fresh fruits (oranges, lemons, bergamots, and apples) and citrus essential oils and evaluate their effect on Mediterranean fruit fly oviposition. There were more than 130 and 45 volatiles compounds detected in fruits odors and citrus essential oils, respectively. The volatile profile of fruits was dominated either from terpenes and terpenoids or from esters of butanoic, hexanoic, and octanoic acids while limonene was by far the most abundant compound in all citrus essential oils. Oviposition of C. capitata was strongly affected by volatiles emanated from both intact fruit and the citrus essential oils. Regarding the volatiles of the intact fruits, the odor of sweet orange elicited strong oviposition responses to females, while bergamot had the least stimulatory effect on oviposition. Bergamot oil also elicited the least oviposition stimulation compared to sweet orange and lemon essential oils. Our discussion elaborates on the role of fruit volatiles on host finding behavior and fruit susceptibility to C. capitata infestation and includes possible practical implication of the above findings.

Polyhydroxy Acids as Fabaceous Plant Components Induce Oviposition of the Common Grass Yellow Butterfly, Eurema Mandarina.

The common grass yellow butterfly, Eurema mandarina is a Fabaceae-feeding species, the females of which readily oviposit on Albizia julibrissin and Lespedeza cuneata in mainland Japan. We previously demonstrated that the methanolic leaf extracts of these plants, and their highly polar aqueous fractions strongly elicit female oviposition. Furthermore, the three subfractions obtained by ion-exchange chromatographic separation of the aqueous fraction have been found to be less effective alone, but synergistically stimulate female oviposition when combined. This indicates that female butterflies respond to multiple compounds with different acidity. We have previously identified d-pinitol from the neutral/amphoteric subfractions and glycine betaine from the basic subfractions as oviposition stimulants of E. mandarina. The present study aimed to identify active compounds in the remaining acidic subfractions of A. julibrissin and L. cuneata leaf extracts. GC-MS analyses of trimethylsilyl-derivatized samples revealed the presence of six compounds in the acidic subfractions. In bioassays using these authentic chemicals, erythronic acid (EA) and threonic acid (TA) were moderately active in eliciting oviposition responses in E. mandarina, with their d-isomers showing slightly higher activity than their l-isomers. Female responsiveness differed between d-EA and l-TA, the major isomers of these compounds in plants, with the response to d-EA reaching a plateau at concentrations above 0.005% and that to l-TA peaking at a concentration of 0.01%. The natural concentrations of d-EA and l-TA in fresh A. julibrissin and L. cuneata leaves were sufficient to stimulate oviposition. Furthermore, mixing 0.001% d-EA or 0.001% l-TA, to which females are mostly unresponsive, with 0.1% d-pinitol resulted in a synergistic enhancement of the oviposition response. These findings demonstrate that E. mandarina females utilize both polyhydroxy acids, EA and TA, as chemical cues for oviposition.

Lactic acid bacteria waste infusion as a source of attraction and oviposition stimulation of gravid female Aedes albopictus mosquitoes.

Aedes albopictus poses a public health risk in tropical countries and temperate countries in recent decades due to its capability to transmit various human arboviruses including dengue, yellow fever, and chikungunya. Vector control is the key for preventing transmission of these pathogenic viruses. Improving the effectiveness of currently utilized collection methods, such as ovitraps, is important for best species abundance monitoring, assessment of the threat of arbovirus transmission, and optimizing control activities. Therefore, this study aimed to assess the potential use of lactic acid bacteria (LAB) waste as an infusion-baited ovitrap for Aedes collection. The performance of overnight tap water, grass hay infusion and LAB waste infusion were compared for their ability in attracting gravid female Ae. albopictus. In this study, the LAB waste infusion was substantially more alluring to Ae. albopictus mosquitoes than the two controls grass hay infusion and tap water.

Effect of Trichosanthes anguina L. flower surface wax chemicals as short-range attractants and oviposition stimulants in Diaphania indica (Saunders) (Lepidoptera: Crambidae)

Larvae of Diaphania indica (Saunders) (Lepidoptera: Crambidae) feed on flowers of Trichosanthes anguina L., and reduce crop production. Therefore, we have tried to find whether flower surface wax chemicals (alkanes and free fatty acids) of three T. anguina cultivars [MNSR-1 (MNS), Baruipur Long (BAR), and Polo No. 1 (POLO)] could act as short-range attractants and oviposition stimulants in females of D. indica. One mg flower surface wax of these cultivars acted as attractants in short Y-tube olfactometer bioassays and stimulated oviposition in females. A synthetic blend of nonadecane, pentacosane, and palmitoleic acid, a synthetic blend of pentacosane and palmitoleic acid, and a synthetic blend of pentacosane and oleic acid in amounts comparable to those present in 1 mg flower surface wax of MNS, BAR, and POLO cultivars, respectively, served as short-range attractants and oviposition stimulants in D. indica. Females exhibited equal egg-laying behavior towards these three synthetic blends when these blends were tested against one another, and hence, these blends could be used as lures in developing baits for traps in pest management strategies.

Genome-Wide Analysis of Odorant and Gustatory Receptors in Six Papilio Butterflies (Lepidoptera: Papilionidae).

Simple SummaryThe butterflies of the Lepidoptera are representatives of herbivorous insects. Host plant diversities may shape the evolution of chemosensory receptors in butterflies. However, little is known about whether the host plant range is correlated with the size differences of chemoreceptors as key molecular targets for butterfly–plant chemical interactions. Here, we characterized 381 odorant (ORs) and 328 gustatory (GRs) receptors in one Papilio generalist and five other Papilio specialists regarding their comprehensive annotation, gene structure, phylogenetics and expression profiles. Among six Papilio species, orthologous ORs or GRs shared conserved gene structure, but the differences in intron size frequencies were observed between the generalist and the specialists. Furthermore, expression profiles identified candidate OR and GR genes in antennae, foretarsi or reproductive tissues of P. xuthus. This study addresses, for the first time, the issue that the breath of host plants does not appear to result in the obvious expansions of ORs and GRs in Papilio butterflies and identifies candidate molecular targets associated with olfaction, oviposition or reproduction in P. xuthus.The chemical interactions of insects and host plants are shaping the evolution of chemosensory receptor gene families. However, the correlation between host range and chemoreceptor gene repertoire sizes is still elusive in Papilionidae. Here, we addressed the issue of whether host plant diversities are correlated with the expansions of odorant (ORs) or gustatory (GRs) receptors in six Papilio butterflies. By combining genomics, transcriptomics and bioinformatics approaches, 381 ORs and 328 GRs were annotated in the genomes of a generalist P. glaucus and five specialists, P. xuthus, P. polytes, P. memnon, P. machaon and P. dardanus. Orthologous ORs or GRs in Papilio had highly conserved gene structure. Five Papilio specialists exhibited a similar frequency of intron lengths for ORs or GRs, but which was different from those in the generalist. Phylogenetic analysis revealed 60 orthologous OR groups, 45 of which shared one-to-one relationships. Such a single gene in each butterfly also occurred in 26 GR groups. Intriguingly, bitter GRs had fewer introns than other GRs and clustered into a large clade. Focusing on the two chemoreceptor gene families in P. xuthus, most PxutORs (52/58) were expressed in antennae and 31 genes in reproductive tissues. Eleven out of 28 foretarsus-expressed PxutGRs were female-biased genes, as strong candidates for sensing oviposition stimulants. These results indicate that the host range may not shape the large-scale expansions of ORs and GRs in Papilio butterflies and identify important molecular targets involved in olfaction, oviposition or reproduction in P. xuthus.

Oviposition stimulants underlying different preferences between host races in the leaf-mining moth Acrocercops transecta (Lepidoptera: Gracillariidae)

The importance of plant chemistry in the host specialization of phytophagous insects has been emphasized. However, only a few chemicals associated with host shifting have been characterized. Herein, we focus on the leaf-mining moth Acrocercops transecta (Gracillariidae) consisting of ancestral Juglans (Juglandaceae)- and derived Lyonia (Ericaceae)-associated host races. The females of the Lyonia race laid eggs on a cover glass treated with an L. ovalifolia leaf extract; the extract was fractionated using silica gel and ODS column chromatography to isolate the oviposition stimulants. From a separated fraction, two analogous Lyonia-specific triterpenoid glycosides were characterized as oviposition stimulants. Furthermore, we observed probable contact chemosensilla on the distal portion of the female antennae. Lyonia race females laid their eggs on the non-host Juglans after the leaves were treated with a Lyonia-specific oviposition stimulant, although they do not lay eggs on Juglans. These results suggest that Lyonia race females do not lay eggs on Juglans leaves because the leaves do not contain specific oviposition stimulant(s). Otherwise, the activity of the oviposition stimulants overcomes oviposition deterrents contained in Juglans leaves. This paper describes the roles of plant chemicals in the different preferences between host races associated with distantly related plant taxa.

Genome-Wide Analysis of Odorant-Binding Proteins in Papilio xuthus with Focus on the Perception of Two PxutGOBPs to Host Odorants and Insecticides.

In this study, we annotated 49 odorant-binding proteins (OBPs) in Papilio xuthus, with four novel genes and seven improved sequences. Expression profiles identified numerous OBPs in antennae or reproductive tissues. Using two antenna-enriched general OBPs (PxutGOBP1 and PxutGOBP2) as targets, we screened three key compounds by a reverse chemical ecology strategy. Of these, an oviposition stimulant vicenin-2 could strongly interact with PxutGOBP1, representing a dissociation constant (Ki) value of 10.34 ± 0.07 μM. Molecular simulations and site-directed mutagenesis revealed the importance of His66, Thr73, and Phe118 between PxutGOBP1 and vicenin-2 interactions. Two other compounds, an ordinary floral scent β-ionone and a widely used insecticide chlorpyrifos, exhibited high affinities to PxutGOBPs (Ki < 13 μM). Furthermore, two mutations His66Ala and Thr73Ala of PxutGOBP1 significantly reduced the binding to chlorpyrifos. Our study provides insights into the putative roles of PxutGOBPs in odorant perception and identifies key binding sites of PxutGOBP1 to vicenin-2 and chlorpyrifos.

Behavioural response of Culex pipiens biotype molestus to oviposition pheromone

Insect behaviour relies on an olfactory sensory system that controls a range of activities, from food choice and mating to oviposition, where pheromones play a central role. In Culex mosquitoes, egg-laying is accompanied by the release of mosquito oviposition pheromone (MOP), which has been shown to affect the oviposition behaviour of conspecifics. Here, we investigated for the first time the effect of MOP on the oviposition rate of Culex pipiens biotype molestus, examining separately males and females, before and after mating and oviposition. Our results demonstrate that MOP is more likely to act as an oviposition stimulant rather than an attractant, since more gravid females laid eggs in its presence, while the number of male or female mosquitoes (virgin or mated) captured on pheromone-treated pots was similar to those treated with control water.

Flower surface wax chemicals in green gram help to stimulate oviposition in Spilosoma obliqua within short distances

AbstractLarvae of Spilosoma obliqua Walker (Lepidoptera: Arctiidae) feed on leaves and flowers of green gram (or mung bean), Vigna radiata (L.) R. Wilczek (Fabaceae), and thereby reduce yield in India. Previously, we demonstrated that leaf surface waxes from three green gram cultivars – PDM 54 (PDM), Pusa Baisakhi (PUSA), and Samrat (SAM) – served as short‐range attractants and oviposition stimulants in S. obliqua. In this study, we aimed to find out whether flower surface waxes have similar roles. We identified the alkanes and free fatty acids in flower surface wax of the three cultivars, created representative blends of synthetic compounds, and tested the effects of crude wax and various blends on attraction and oviposition of S. obliqua. Twenty‐two n‐alkanes (n‐C13 to n‐C36) were identified in PDM, and 23 in the other two cultivars; pentadecane was predominant. Fifteen free fatty acids (C12:0 to C22:0) were detected in the three cultivars; palmitoleic acid (in PDM and PUSA) and pentadecanoic acid (in SAM) were predominant. In Y‐tube olfactometer bioassays, females were attracted to 1 mg flower surface wax of the three cultivars, as well as to blends composed of 3–7 compounds representative of the three varieties (PDM: tricosane, pentacosane, heptacosane, nonacosane, palmitoleic acid, linolenic acid, and stearic acid; PUSA: heptacosane, nonacosane, and stearic acid; and SAM: heptacosane, linolenic acid, and stearic acid). In dual choice tests, the females did not distinguish between surface wax of a variety and its representative synthetic blend. Also, they did not distinguish between the three cultivars. Results of oviposition assays were similar: 1 mg flower surface wax, as well as synthetic blends, stimulated egg laying, but the numbers of eggs were similar in the presence of surface wax of a variety vs. its representative synthetic blend. Also, oviposition was not differentially affected by cultivar. Thus, as in leaves, flower surface waxes act as short‐range attractants and oviposition stimulants in S. obliqua. The blends are potentially of use to develop lures as part of integrated pest management strategies.

Seminal fluid proteins induce transcriptome changes in the Aedes aegypti female lower reproductive tract

BackgroundMating induces behavioral and physiological changes in the arbovirus vector Aedes aegypti, including stimulation of egg development and oviposition, increased survival, and reluctance to re-mate with subsequent males. Transferred seminal fluid proteins and peptides derived from the male accessory glands induce these changes, though the mechanism by which they do this is not known.ResultsTo determine transcriptome changes induced by seminal proteins, we injected extract from male accessory glands and seminal vesicles (MAG extract) into females and examined female lower reproductive tract (LRT) transcriptomes 24 h later, relative to non-injected controls. MAG extract induced 87 transcript-level changes, 31 of which were also seen in a previous study of the LRT 24 h after a natural mating, including 15 genes with transcript-level changes similarly observed in the spermathecae of mated females. The differentially-regulated genes are involved in diverse molecular processes, including immunity, proteolysis, neuronal function, transcription control, or contain predicted small-molecule binding and transport domains.ConclusionsOur results reveal that seminal fluid proteins, specifically, can induce gene expression responses after mating and identify gene targets to further investigate for roles in post-mating responses and potential use in vector control.

Short-range attraction and oviposition stimulant of a biocontrol agent, Galerucella placida Baly (Coleoptera: Chrysomelidae) toward weed leaf surface waxes.

Two Polygonaceae weeds, Rumex dentatus L. and Polygonum glabrum Willd. are abundant in wheat- and rice-fields, respectively, in India. Galerucella placida Baly (Coleoptera: Chrysomelidae) is a biocontrol agent of these two weeds. The importance of long-chain alkanes and free fatty acids present in leaf surface waxes of these weeds was assessed as short-range attractant and ovipositional stimulant in G. placida females. Extraction, TLC, GC-MS and GC-FID analyses demonstrated 19 n-alkanes from n-C14 to n-C35 and 14 free fatty acids from C12:0 to C22:0 in leaf surface waxes. Hentriacontane was predominant among alkanes in both weeds, while oleic acid and docosanoic acid were predominant among free fatty acids in R. dentatus and P. glabrum, respectively. Females of G. placida were attracted toward one leaf equivalent surface wax of both weeds against the control solvent (petroleum ether) in a short Y-tube olfactometer bioassay. But, the insect could not differentiate between one leaf equivalent surface wax of R. dentatus and P. glabrum, indicating that both weed leaves were equally attractive in females. A synthetic blend of either 2.44, 35.57 and 23.58 μg ml-1 of octadecane, heptacosane and nonacosane, respectively, resembling the amounts present in one leaf equivalent surface wax of R. dentatus or 4.08, 19.54 and 23.58 μg ml-1 of octadecane, palmitoleic acid and docosanoic acid, respectively, resembling the amounts present in one leaf equivalent surface wax of P. glabrum acted as short-range attractant and ovipositional stimulant in G. placida. These results could be a basis for host plant specificity of the biocontrol agent.

Volatile chemical signals underlying the host plant preferences of Tuta absoluta

AbstractThe South American leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a serious pest of tomato causing substantial annual economic losses at a global scale. Our study comprised choice and no‐choice bioassays, aimed at understanding the preference of this oligophagous pest for a few selected solanaceous hosts (tomato, potato, eggplant, ashwagandha, black nightshade, wild tomato, tobacco, and datura), and the identification of the volatile cues that influence its host selection process. In choice assays, T. absoluta females preferred tomato for oviposition over all the other plants, whereas ashwagandha, tobacco, and datura were the least preferred; on datura zero eggs were laid. A similar trend was observed in the subsequent number of larval mines formed. The moth’s preference for host plants of the genus Solanum was quite evident in both the choice and no‐choice assays. Tomato plant volatiles were found to be more attractive to the female moths in single‐ and dual‐choice olfactometer assays. In electroantennographic bioassays, the mean depolarization was significant for tomato, potato, ashwagandha, and eggplant compared to empty air and honey. In total 76 volatile compounds were identified in the GC‐MS analysis across the eight previously selected host–plant headspace samples. Principal component analysis revealed that 1‐fluorododecane and p‐quinone mainly contributed to the observed variation among the host plant volatiles. Of all the host plants, tomato, wild tomato, and tobacco were found to share similarities with respect to volatile cues, whereas ashwagandha, eggplant, and datura were found to be closely related. The other two hosts, potato and black nightshade, had fewer volatiles in common. Volatile cues, namely p‐quinone, 2‐carene, δ‐curcumene, and 1,2‐diethylbenzene, in tomato could serve as oviposition stimulants to T. absoluta, whereas the presence of 1‐fluorododecane in host plants such as datura, eggplant, ashwagandha, and black nightshade, might have deterred T. absoluta from ovipositing. 1‐Fluorododecane was found to be completely absent in tomato.

Leaf Surface Wax Chemicals in Trichosanthes anguina (Cucurbitaceae) Cultivars Mediating Short-Range Attraction and Oviposition in Diaphania indica.

Larval Diaphania indica (Saunders) (Lepidoptera: Crambidae) cause complete defoliation of Trichosanthes anguina L. and reduce crop yield in India. Females lay eggs on the leaf surface, and therefore leaf surface waxes are potentially involved in host selection. Alkanes and free fatty acids are the major constituents of leaf surface waxes, so a study was conducted to determine whether these wax constituents from three T. anguina cultivars (MNSR-1, Baruipur Long, and Polo No.1) could act as short-range attractants and oviposition stimulants in D. indica females. Twenty n-alkanes from n-C14 to n-C36 and 13 free fatty acids from C12:0 to C21:0 were detected in the leaf surface waxes of these cultivars. Heptadecane and stearic acid were predominant among n-alkanes and free fatty acids, respectively, in these cultivars. Females showed attraction towards one leaf equivalent surface wax of each of these cultivars against solvent controls (petroleum ether) in Y-tube olfactometer bioassays. A synthetic blend of heptadecane, eicosane, hexacosane, and stearic acid, a synthetic blend of hexacosane and stearic acid, and a synthetic blend of pentadecane and stearic acid comparable to amounts present in one leaf equivalent surface wax of MNSR-1, Baruipur Long, and Polo No.1, respectively, were short-range attractants and oviposition stimulants in D. indica. Female egg laying responses were similar to each of these blends, providing information that could be used to developing baited traps in integrated pest management (IPM) programs.

Mating status of coexisting conspecific individuals modulate reproduction in a ladybird, Menochilus sexmaculatus

Abstract The mating status of organisms plays a crucial role in deciphering mating decision and reproductive success of any organisms. Odour or pheromones are known to be perceived by animals through olfaction to locate mates at a distance. In this study, an attempt was made to investigate the effect of the presence of unmated and mated conspecific adults on mating and reproductive parameters of the ladybird beetle, Menochilus sexmaculatus (Fabricius, 1781). To conduct this experiment, an arena was made with the help of two Petri dishes and in such a manner that the experimental adults were only able to perceive the presence of conspecific adults of different mating status in their close vicinity. The results of the study demonstrated an early onset of mating in the presence of males compared to females. Another male in the vicinity poses competition that may force the males to establish genital contact faster. In the absence of any potential rival, copulation duration was highest. Females laid more eggs in the presence of mated females. This may be to increase offspring fitness in the presence of potential competitors for the already mated female. Females laid fewer eggs in the presence of unmated females. Unmated females nearby can be another choice for a male and thus, the male possibly limits the size of the ejaculate containing oviposition stimulants. The current study advocates that mating and reproductive behaviour are modulated according to the perceived surroundings in the form of conspecific adults of different mating status.