Specialist Insect Research Articles

A Comparative Study of Blue and Yellow Sticky Traps for Insect Monitoring on Tomato Organic Farm in Mardi Cameron Highlands

Sticky traps are widely used tools in insect monitoring and pest management strategies. These traps are useful tools for monitoring insect populations and eradicating pests because they use a sticky adhesive surface to capture and immobilize insects upon contact, especially flying insects. This study focuses on investigating insect preferences in a tomato plot regarding their attraction to either blue or yellow sticky traps. The research was conducted over three sampling periods from October to November 2022. A total of 12 sticky traps were deployed in the tomato plot for each sampling time, with six blue and six yellow sticky traps. Results of t test indicated a significant difference between the insects captured using Yellow Sticky Traps (YST) and Blue Sticky Traps (BST) with p value < 0.05 (t value = 2.94). The data indicated that YST was better at capturing a greater variety of insects, enhancing diversity coverage. On the other hand, BST demonstrated its significance in monitoring thrips and aphids, pests crucial to tomatoes, making it valuable for insect surveillance. In conclusion, YST demonstrated higher overall insect capture rates, BST remained valuable for specific insects like thrips and aphids. The findings from this study provide valuable insights for optimizing insect trapping methods in tomato cultivation and potentially in other agricultural settings.

Low seed viability of a rare aster

The reproductive ecology of rare plants is often unknown, yet the persistence of most plant populations depends on successful interactions with pollinators and favourable environmental conditions. Sexual reproduction maintains genetic diversity within plant populations using pollinators to transport pollen grains among plants of the same species and producing seeds. We investigated the reproduction of Yermo xanthocephalus Dorn (Desert yellowhead), a perennial member of Asteraceae endemic to central Wyoming, USA, which grows in only two locations within 8 km of each other. Our objectives were to assess the pollination and seed-set of Y. xanthocephalus. We conducted seed-set experiments in both populations to measure self-pollination and estimate if pollinating insects limited seed production. We used vane traps and pan traps to capture pollinators, and we examined pollen carried on bees. Yermo xanthocephalus can self-pollinate, but seed-set was extremely low. The number of viable seeds produced in flowerheads pollinated by insects did not differ from those produced by capitula hand-pollinated with excess pollen, indicating that pollinators did not limit seed production that year. Pollen from Y. xanthocephalus was carried by nine bee genera, suggesting that no one specific insect pollinates this plant. Only 12% of ovules produced viable seeds in the main population and 0% were viable in the other population, suggesting that something beyond pollinators limited seed-set. We recommend continued research to address what is limiting seed production to advance the knowledge and management of this declining plant species.

The Diversity of pollinator insects in vegetable gardens, Kabawo District, Muna Regency

Pollinator insects play an important role in pollination to increase the productivity of flowering plants. The aim of this study was to analyze the abundance, diversity, and specific taxon of insect pollinators among different vegetable crops in local farmers' gardens. Insects were sampled from four gardens, namely polyculture long bean (KKP), eggplant polyculture (KT), curly chili monoculture (KCK), and Indofood chili monoculture (KCI) used nets and light traps. The results showed that the abundance and diversity of pollinator insects varied between gardens. The pollinator insect community in KCI was most similar to that in KCK; KT was similar to the KCI and KCK groups, while KKP were separate from the KT, KCK and KCI groups. The richest genus occurs in KKP, while chili plantations are the poorest. The apis genus in KKP and KT, and the Nomina genus in KCK and KCI were dominant. The specific pollinator insect genus in KKP is the richest. It concluded that plant species and cropping patterns contribute to the composition and diversity of the pollinator insect community.

UDP-glycosyltransferases act as key determinants of host plant range in generalist and specialist Spodoptera species

Phytophagous insects have evolved sophisticated detoxification systems to overcome the antiherbivore chemical defenses produced by many plants. However, how these biotransformation systems differ in generalist and specialist insect species and their role in determining insect host plant range remains an open question. Here, we show that UDP-glucosyltransferases (UGTs) play a key role in determining the host range of insect species within the Spodoptera genus. Comparative genomic analyses of Spodoptera species that differ in host plant breadth identified a relatively conserved number of UGT genes in generalist species but high levels of UGT gene pseudogenization in the specialist Spodoptera picta. CRISPR-Cas9 knockouts of the three main UGT gene clusters of Spodoptera frugiperda revealed that UGT33 genes play an important role in allowing this species to utilize the poaceous plants maize, wheat, and rice, while UGT40 genes facilitate utilization of cotton. Further functional analyses in vivo and in vitro identified the UGT SfUGT33F32 as the key mechanism that allows generalist S. frugiperda to detoxify the benzoxazinoid DIMBOA (2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one), a potent insecticidal phytotoxin produced by poaceous plants. However, while this detoxification capacity is conserved in several generalist Spodoptera species, Spodoptera picta, which specializes on Crinum plants, is unable to detoxify DIMBOA due to a nonfunctionalizing mutation in SpUGT33F34. Collectively, these findings provide insight into the role of insect UGTs in host plant adaptation, the mechanistic basis of evolutionary transitions between generalism and specialism and offer molecular targets for controlling a group of notorious insect pests.

Geographic distribution of terpenoid chemotypes in Tanacetum vulgare mediates tansy aphid occurrence but not abundance

Intraspecific variation of specialized metabolites in plants, such as terpenoids, are used to determine chemotypes. Tansy Tanacetum vulgare exhibits diverse terpenoid profiles that affect insect communities. However, it is not fully known whether patterns of their chemical composition and associated insects vary beyond the community scale. Here, we investigated the geographic distribution of mono‐ and sesquiterpenoid chemotypes in tansy leaves and their relationships with specific insect communities across Germany. We sampled tansy leaves from ten plants with and five plants without aphids in each of 26 sites along a north–south and west–east transect in Germany. Hexane‐extracted metabolites from leaf tissues were analyzed by gas chromatography‐mass spectrometry (GC‐MS). Plant morphological traits, aphid occurrence and abundance, and occurrence of ants were recorded locally. The effect of plant chemotype, plant morphological parameters, and abiotic site parameters such as soil types, temperature and precipitation on insect occurrences were analyzed. Plants clustered into four monoterpenoid and four sesquiterpenoid chemotype classes. Monoterpene classes differed in their latitudinal distribution, whereas sesquiterpenes were more evenly distributed across the transect. Aphid and ant occurrence was influenced by monoterpenoids. Plants of monoterpenoid class 1 were colonized by aphids and ants significantly more often than expected by chance, whereas in other classes there were no significant differences. Aphid abundance was affected by soil type, and average annual temperature positively correlated with the occurrence of ants. We found significant geographic patterns in the distribution of tansy chemodiversity and show that monoterpenoids affect aphid and ant occurrence, while the soil type can influence aphid abundance. We show that geographic variation in plant chemistry influences insect community assembly on tansy plants.

Gut microbiota metagenomics and mediation of phenol degradation in Bactrocera minax (Diptera, Tephritidae).

Gut microbiota mediating insect-plant interactions have many manifestations, either by provisioning missing nutrients, or by overcoming plant defensive reactions. However, the mechanism by which gut microbiota empower insects to survive by overcoming a variety of plant secondary metabolites remains largely unknown. Bactrocera minax larvae develop in immature citrus fruits, which present numerous phenolic compounds that challenge the larvae. To explore the role of gut microbes in host use and adaptability, we uncovered the mechanisms of phenol degradation by gut microbes using metagenomic and metatranscriptomic analyses, and verified the degradation ability of isolated and cultured bacteria. Research on this subject can help develop potential strain for the environmental friendly pest management operations. We demonstrated the ability of gut microbes in B. minax larvae to degrade phenols in unripe citrus. After antibiotic treatment, coniferyl alcohol and coumaric aldehyde significantly reduced the survival rate, body length and body weight of the larvae. The metagenomic and metatranscriptomic analyses in B. minax provided evidence for the presence of genes in bacteria and the related pathway involved in phenol degradation. Among them, Enterococcus faecalis and Serratia marcescens, isolated from the gut of B. minax larvae, played critical roles in phenol degradation. Furthermore, supplementation of E. faecalis and S. marcescens in artificial diets containing coniferyl alcohol and coumaric aldehyde increased the survival rate of larvae. In summary, our results provided the first comprehensive analysis of gut bacterial communities by high-throughput sequencing and elucidated the role of bacteria in phenol degradation in B. minax, which shed light on the mechanism underlying specialist insect adaption to host secondary metabolites via gut bacteria. © 2024 Society of Chemical Industry.

Understanding consumers attitude towards insects as food: Influence of insect species on liking, emotions, sensory perception and food pairing

Entomophagy studies mainly focused on insects as a generic category, rarely considering insect species. This study investigated the: i) affective response to specific edible insect species; ii) sensory properties characterizing the tested insects and their role in driving preferences and food paring. A sensory test (85 consumers, 56.5 % female, 19–73 years) was performed on seven dried whole edible insects at the adult (weaver ants, crickets, grasshoppers), larva (bamboo worms, morio worms, sago worms) and pupae stage (silkworms). For each species, consumers expressed their liking and, through three check-all-that-apply tests, described the perceived sensory properties, the perceived emotions, and their potential food pairings. Results showed a significant effect of the species on all variables. Bamboo worms, weaver ants and grasshoppers resulted the most accepted, followed by morio worms, crickets, and silkworms, while the sago worms were the most disliked. Numerous sensory attributes significantly discriminated among insect species and the drivers of liking and sensory attributes associated to the food pairings were identified. However, two clusters with different preferences and drivers of liking were observed. Moreover, a gender effect was found: i) males associated insects with emotions like calm and wild, while females with glad and pleased; ii) males and females would pair different foods with the insect species. In conclusion, this study provided new knowledge useful for researchers and food industry to develop future insect-based foods and dishes able to meet the expectations of different consumers segments.

GC-MS-based Metabolomics Unravels Metabolites across Larval Development and Diapause of a Specialist Insect.

Plant-insect interactions are a driving force into ecosystem evolution and community dynamics. Many insect herbivores enter diapause, a developmental arrest stage in anticipation of adverse conditions, to survive and thrive through seasonal changes. Herein, we investigated the roles of medium- to non-polar metabolites during larval development and diapause in a specialist insect herbivore, Chlosyne lacinia, reared on Aldama robusta leaves. Varying metabolites were determined using gas chromatography-mass spectrometry (GC-MS)-based metabolomics. Sesquiterpenes and steroids were the main metabolites putatively identified in A. robusta leaves, whereas C. lacinia caterpillars were characterized by triterpenes, steroids, fatty acids, and long-chain alkanes. We found out that C. lacinia caterpillars biosynthesized most of the identified steroids and fatty acids from plant-derived ingested metabolites, as well as all triterpenes and long-chain alkanes. Steroids, fatty acids, and long-chain alkanes were detected across all C. lacinia instars and in diapausing caterpillars. Sesquiterpenes and triterpenes were also detected across larval development, yet they were not detected in diapausing caterpillars, which suggested that these metabolites were converted to other molecules prior to the diapause stage. Our findings shed light on the chemical content variation across C. lacinia development and diapause, providing insights into the roles of metabolites in plant-insect interactions.

Post-ingestive stability of a mulberry Kunitz-type protease inhibitor MnKTI-1 in the digestive lumen of silkworm: dual inhibition towards α-amylase and serine protease.

Adaptation of specialist insects to their host plants and defense responses of plants to phytophagous insects have been extensively recognized while the dynamic interaction between these two events has been largely underestimated. Here, we provide evidence for characterization of an unrevealed dynamic interaction mode of digestive enzymes of specialist insect silkworm and inhibitor of its host plant mulberry tree. MnKTI-1, a mulberry Kunitz-type protease inhibitor, whose messenger RNA (mRNA) transcription and protein expression in mulberry leaf were severely triggered and up-regulated by tens of times in a matter of hours in response to silkworm, Bombyx mori, and other mulberry pest insects, suggesting a quick response and broad spectrum to insect herbivory. MnKTI-1 proteins were detected in gut content and frass of specialist B. mori, and exhibited significant post-ingestive stability. Recombinant refolded MnKTI-1 (rMnKTI-1) displayed binding affinity to digestive enzymes and a dual inhibitory activity to α-amylase BmAmy and serine protease BmSP2956 in digestive juice of silkworm. Moreover, data from in vitro assays proved that the inhibition of recombinant rMnKTI-1 to BmAmy can be reverted by pre-incubation with BmSP15920, an inactivated silkworm digestive protease that lack of complete catalytic triad. These findings demonstrate that mulberry MnKTI-1 has the potential to inhibit the digestive enzyme activities of its specialist insect herbivore silkworm, whereas this insect may employ inactivated proteases to block protease inhibitors to accomplish food digestion. The current work provides an insight to better understand the interacting mode between host plant Kunitz protease inhibitors and herbivorous insect digestive enzymes. © 2024 Society of Chemical Industry.

Insight into insect odorant binding proteins: An alternative approach for pest management

Insects have enormous impact on public health as agricultural pests and disease vectors worldwide. Olfaction is the most crucial recognition process that mediates chemical communication in insects. Odorant binding proteins (OBP) are the small soluble proteins present in the sensory organs of the insects and are involved in many behavioural contexts, such as locating host, mating partners, escaping predators, flight, hygrosensation, immunity and identifying oviposition sites. OBPs are typically thought to function as a molecular carrier that bind, solubilize, and transport hydrophobic odorant molecules through the sensillar fluid and protect them from odorant degradation, thus maximizing olfactory system’s sensitivity. Due to their large structural and functional diversity, OBPs can be used as molecular targets for species, stage and sex specific insect pest management. In this review article, we will explore the structural and functional aspects of insect OBP and its potential applications in insect pest management. Antennal transcriptomics, ligand binding assay, olfactory repellents, pheromone-based disruption, RNA interference (RNAi) and genetic modifications can be effective management tactics for insect pests.

A test of trade-offs in dispersal and reproduction within and between a sister species pair of specialist insect herbivores.

Understanding the drivers of trade-offs among traits is vital for comprehending the evolution and maintenance of trait variation. Theoretical frameworks propose that evolutionary mechanisms governing trade-offs frequently exhibit a scale-dependent nature. However, empirical tests of whether trade-offs exhibited across various biological scales (i.e. individuals, populations, species, genera, etc.) remains scarce. In this study, we explore trade-off between dispersal and reproductive effort among sympatric sister species of wasps in the genus Belonocnema (Hymenoptera: Cynipini: Cynipidae) that form galls on live oaks: B. fossoria, which specializes on Quercus geminata, and B. treatae, which specializes on Q. virginiana. Specifically, our results suggest that B. fossoria has evolved reduced flight capability and smaller wings, but a larger abdomen and greater total reproductive effort than B. treatae, which has larger wings and is a stronger flier, but has a smaller abdomen and reduced total reproductive effort. These traits and the relationships among them remain unchanged when B. fossoria and B. treatae are transplanted and reared onto the alternative host plant, suggesting that trait divergence is genetically based as opposed to being a plastic response to the different rearing environments. However, when looking within species, we found no evidence of intraspecific trade-offs between wing length and reproductive traits within either B. fossoria or B. treatae. Overall, our results indicate that observed trade-offs in life history traits between the two gall former species are likely a result of independent adaptations in response to different environments as opposed to the amplified expression of within species intrinsic tradeoffs.

Diversity, Composition, and Specificity of the Philaenus spumarius Bacteriome.

Philaenus spumarius (Linnaeus, 1758) (Hemiptera, Aphrophoridae) was recently classified as a pest due to its ability to act as a vector of the phytopathogen Xylella fastidiosa. This insect has been reported to harbour several symbiotic bacteria that play essential roles in P. spumarius health and fitness. However, the factors driving bacterial assemblages remain largely unexplored. Here, the bacteriome associated with different organs (head, abdomen, and genitalia) of males and females of P. spumarius was characterized using culturally dependent and independent methods and compared in terms of diversity and composition. The bacteriome of P. spumarius is enriched in Proteobacteria, Bacteroidota, and Actinobacteria phyla, as well as in Candidatus Sulcia and Cutibacterium genera. The most frequent isolates were Curtobacterium, Pseudomonas, and Rhizobiaceae sp.1. Males display a more diverse bacterial community than females, but no differences in diversity were found in distinct organs. However, the organ shapes the bacteriome structure more than sex, with the Microbacteriaceae family revealing a high level of organ specificity and the Blattabacteriaceae family showing a high level of sex specificity. Several symbiotic bacterial genera were identified in P. spumarius for the first time, including Rhodococcus, Citrobacter, Halomonas, Streptomyces, and Providencia. Differences in the bacterial composition within P. spumarius organs and sexes suggest an adaptation of bacteria to particular insect tissues, potentially shaped by their significance in the life and overall fitness of P. spumarius. Although more research on the bacteria of P. spumarius interactions is needed, such knowledge could help to develop specific bacterial-based insect management strategies.

Patterns of insecticide uses and its impact on the health of the farmers in Tangail district of Bangladesh

Appropriate and judicious application of insecticide is the most effective measure of crop protection against the injury and damage of insect pests. However, the tendency of the farmers is to apply insecticide without maintaining proper dose, time and precautionary measures. This study was conducted in Dhanbari and Madhupur upazilas of the Tangail district during July to October 2020 to find out the patterns of insecticide use on summer vegetables and the potential risks of insecticides on the health of farmers. Data were collected from randomly selected 120 farmers through a pre-tested questionnaire. The majority of farmers within the study area obtained information regarding specific insect pests and the recommended insecticide from local retailer shops 81.7%), whereas information on insecticide dosage was primarily gathered from experts (91.7%). In the study area, farmers applied insecticides once/twice a season (66.7%). The survey report showed that 60.0% of the farmers applied insecticides without reading the label information, while all the farmers applied insecticides using hand driven sprayer machine between the hours of 10 am to 3 pm. Results revealed that 63.3% of the farmers took a moderate protective measures, but 93.3% did not consider pre-harvest Interval (PHI). A considerable portion of farmers (48.3%) kept pesticide bottles and packaging alongside other inputs, while most respondents (96.6%) disposed of these items in the fields. It was found that 70.0% of the farmers were acquainted with health hazards, 56.6% knew about water pollution, 54.1% knew about reduction of pollinators due to insecticide application. Based on the perspectives of the participants, it was also found that, 60.0% farmers suffered from physical weakness, 55.0% suffered in loss of appetite, 38.3% suffered in eye irritation, 28.3% experienced in body itching, and 12.7% suffered urinary and sexual disorder. Ann. Bangladesh Agric. (2023) 27 (1): 31-39

Dietary experience alters predatory behavior of two ladybird species on tomato potato psyllid.

The tomato potato psyllid, Bactericera cockerelli, is an invasive pest in Australia, which can cause severe economic loss in the production of Solanaceous crops. As an invasive pest, B. cockerelli may also modify biotic interactions in Australian agricultural and native ecosystems. Resident generalist predators in an area may have the ability to utilize invasive pest species as prey but this will depend on their specific predatory behavior. The extent to which generalist predators learn from their previous dietary experience (i.e., whether they have used a particular species as prey before) and how this impacts subsequent prey choice will influence predator and prey population dynamics after invasion. In this study, one nonnative resident ladybird, Hippodamia variegata, and one native ladybird, Coccinella transversalis, were investigated. Dietary experience with B. cockerelli as a prey species significantly increased preference for the psyllid in a short term (6 h) Petri dish study where a choice of prey was given. Greater suppression of B. cockerelli populations by experienced ladybirds was also observed on glasshouse grown tomato plants. This was presumably due to altered prey recognition by experience. The result of this study suggest the potential to improve the impact of biological control agents on invasive pests by providing early life experience consuming the target species. It may prove valuable for developing improved augmentative release strategies for ladybirds to manage specific insect pest species.

An updated data on bionomics of walnut weevil, Alcidodes porrectirostris Marshal (Coleoptera: Curculionidae) under laboratory conditions and its extent of damage in Juglans regia (L.) of the Kashmir valley, India

Walnut is one of the most important fruits, which has been defined as a "Superfood" in recent years. It is infected by a wide array of insect pests. Among these pests, the walnut weevil is a destructive one. Its adults feed on flowers and buds while its larvae feed inside the fruits and are extremely destructive in causing premature dropping. We report two generations of walnut weevil in a year and only a single larva per fruit. Adults emerge from the soil in April and feed on walnut leaf buds, petioles of leaves, and floral buds. Adult females lay 1-2 eggs on fruits, mainly in May and early June, hatch in 4.9±0.74 (SD) days and 4.5±0.97 days in the first and second generations. They develop through three instars and the total developmental time lies in the range of 46-55 days (49.1±2.51). The adults of the second generation undergo overwintering to avoid harsh environmental conditions. Comprehension of biology, life cycles, and the nature of damage aids in keeping track of specific insect pests at the proper time.

Beauveria bassiana transcriptomics reveal virulence-associated shifts during insect lipid assimilation.

Insect cuticular lipids, especially epicuticular hydrocarbons (CHC), have a significant role in insect ecology and interactions with other organisms, including fungi. The CHC composition of a specific insect species may influence the outcome of the interaction with a specific fungal strain. Some insects, such as Piezodorus guildinii, have low susceptibility towards fungal infections seemingly due to their CHC composition. The entomopathogenic fungus Beauveria bassiana can assimilate CHC and incorporate them as building blocks via cytochrome P450 monooxygenases (CYPs). However, little is known about other enzymes that promote the degradation/assimilation of these cuticular components. In this study, we performed a transcriptomic analysis to evaluate the in vitro response of two virulence-contrasting B. bassiana strains when grown on three different P. guildinii CHC sources. We found a different expression profile of virulence-related genes, as well as different GO and KEGG parameters enriched at 4 days post-inoculation, which could help account for the intrinsic virulence and for an alkane-priming virulence enhancement effect. The hypovirulent strain predominantly showed higher expression of cuticle penetration genes, including chitinases, proteases, and CYPs, with GO term categories of "heme binding," "monooxygenase activity," and "peroxisome" pathways enriched. The hypervirulent strain showed higher expression of cell wall remodeling and cell cycle genes, and cuticle adhesion and a distinct set of CYPs, with GO categories of "DNA-binding transcription factor activity" and KEGG pathways corresponding to "meiosis-yeast" and "cell cycle" enriched. These results suggest a delay and alternate routes in pathogenicity-related metabolism in the hypovirulent strain in comparison with the hypervirulent strain. KEY POINTS: •Transcriptomics of two B. bassiana strains grown in P. guildinii cuticular components •Virulence-related genes correlated with virulence enhancement towards P. guildinii •Differentially expressed genes, GOs and KEGGs showed different metabolic timelines associated with virulence.

Novel host plant use by a specialist insect depends on geographic variation in both the host and herbivore species

Understanding the circumstances under which insect herbivores will adopt a novel host plant is a longstanding question in basic and applied ecology. While geographic variation in host use can arise through differences in both herbivore preference and plant characteristics, there is a tendency to attribute geographic variation in host use to regional differences in herbivore preference alone. This is especially true for herbivores specialized to one or a few plant species. We compared how geographic variation in herbivore preference and host plant origin shape regional differences in host plant use by the specialized herbivore, Euphydryas phaeton. In parts of its range, E. phaeton uses only a native host, Chelone glabra, while in others, it also uses an introduced host, Plantago lanceolata. We offered female butterflies from each region the non-native host plant sourced from both regions and compared their oviposition behavior. The non-native host was almost universally rejected by butterflies in the region where only the native plant is used. In the region where butterflies use both hosts, females accepted non-native plants from their natal region twice as often as non-native plants from the other region where they are not used. Acceptance differed substantially among individual butterflies within regions but not among plants within regions. Thus, both individual preference and regional differences in both the insect and non-native host contributed to the geographic variation in different ways. These results highlight that, in addition to herbivore preference, regional differences in perceived plant suitability may be an important driver of diet breadth.

Chemosensory detection of glucosinolates as token stimuli for specialist insects on brassicaceous plants: discovery and impact.

In this paper, we take a historical perspective by going back to Verschaffelt's landmark study published in 1910, in which he found that glucosinolates were used as token stimuli by larvae of Pieris butterflies, specialist feeders on plants in the family Brassicaceae. This classic discovery provided key evidence for Fraenkel(Science 129:1466-1470, 1959) to elaborate on the function of secondary plant substances and for Ehrlich and Raven(Evolution 18:586-608, 1964) to put forward the hypothesis of insect-plant coevolution. The discovery by Schoonhoven (Kon Nederl Akad Wetensch Amsterdam Proc Ser C70:556-568, 1967) of taste neurons highly sensitive to glucosinolates in Pieris brassicae was an important milestone in elucidating the chemosensory basis of host-plant specialization. The molecular basis of glucosinolate sensitivity was elucidated recently (Yang et al., PLoS Genet 17, 2021) paving the way to unravel the evolution of gustatory receptors tuned to glucosinolates that are crucial for host-plant selection of Pieris butterflies. We propose a hypothetical model for the evolution of labeled-line neurons tuned to token stimuli.

Selection pressure by specialist and generalist insect herbivores leads to optimal constitutive plant defense. A mathematical model.

Brassicaceae plants have the glucosinolate-myrosinase defense system, jointly active against herbivory. However, constitutive glucosinolate (GLS) defense is observed to occur at levels that do not deter all insects from feeding. That prompts the question of why Brassicaceae plants have not evolved a higher constitutive defense. The answer may lie in the contrasting relationship between plant defense and host plant preference of specialist and generalist herbivores. GLS content increases a plant's susceptibility to specialist insects. In contrast, generalists are deterred by the plant GLSs. Although GLSs can attract the natural enemies (predators and parasitoids) of these herbivores, enemies can reduce herbivore pressure to some extent only. So, plants can be overrun by specialists if GLS content is too high, whereas generalists can invade the plants if it is too low. Therefore, an optimal constitutive plant defense can minimize the overall herbivore pressure. To explain the optimal defense theoretically, we model the contrasting host selection behavior of insect herbivores and the emergence of their natural enemies by non-autonomous ordinary differential equations, where the independent variable is the plant GLS concentration. From the model, we quantify the optimal amount of GLSs, which minimizes total herbivore (specialists and generalists) pressure. That quite successfully explains the evolution of constitutive defense in plants from the perspective of optimality theory.

Contact toxicity and proximate effect of fipronil on insect pest and predatory ant community structure in cocoa agro-ecosystem

Although usage persists in some countries, fipronil is banned or restricted in many others. Prior to its ban on cocoa in Ghana, concerns about its effect on non-target insects and secondary outbreak of Anomis leona were conflicting. This study, which predates the ban, assessed the toxicity and the short-term effect of fipronil on specific insect community structure in the cocoa agro-ecosystem alongside bifenthrin and a non-insecticide control. Although the insecticides induced a high mortality (90-100%) on the target (mirid: Sahlbergella singularis, stink bug: Bathycoelia thalassina and coreid bug: Pseudotheraptus devastans) and non-target (ants: Oecophylla longinoda, Crematogaster africana, Pheidole megacephala and Camponotus consobrinus) insects, the knockdown to fipronil was very low compared to bifenthrin. On the field, fipronil was more detrimental to the ants. Insecticide-treated plots recorded relatively lower post-treatment pest diversity compared to the control, except the last sampling month while ant abundance, richness and diversity were lowest on the fipronil-treated plots at the end of the study period. This study demonstrates that although fipronil was effective against pests and did not result in acute secondary pest outbreak, it was harmful to the ants. This effect could potentially be replicated on these ant species in other cropping systems where the insecticide is used, adversely affecting ecosystem service delivery. Hence, research on its impact on non-target organisms in other cropping systems is needed to regulate and monitor its use.