How omnivory affects the survival and choices of earwig Doru luteipes (Scudder) (Dermaptera: Forficulidae)?

Doru luteipes (Scudder, 1876) is an omnivorous predator that finds different food resources in the corn plant: eggs of Spodoptera frugiperda (J.E. Smith, 1797), uredospores of Puccinia polysora (Underw, 1897), and pollen. Knowing the survival and food preferences of this predator is essential to define its relevance as a biological control agent. We hypothesize that the foraging behavior and predatory capacity of D. luteipes may be affected when several food resources, especially eggs of S. frugiperda, uredospores of P. polysora, and pollen are concurrently in the same plant. The survival of D. luteipes in the nymph stage and their preference among food resources, often available in corn plants, were determined. To verify the survival of D. luteipes, newly hatched nymphs were fed exclusively with 1- uredospores of P. polysora, 2- eggs of S. frugiperda, 3- corn pollen, 4- a combination of uredospores + eggs, and 5- artificial diet (control). In another experiment, nymphs and adults of D. luteipes with 24 and 48 hours of fasting were individually released in the center of a container with four diets: 1- uredospores of P. polysora, 2- eggs of S. frugiperda, 3- corn pollen, 4- artificial diet, and maintained for 10 minutes, to evaluate the food choice and feeding time. The exclusive feeding with S. frugiperda eggs caused low nymph survival (8%), but the combination of P. polysora uredospores + S. frugiperda eggs allowed 58.3% survival. D. luteipes preferred feeding during the nighttime and the most significant proportions of choices by nymphs and adults were for pollen and diet, with adults spending more time eating pollen. These findings indicate that the trophic choices of D. luteipes are relevant to understand its contribution as an agent to control pest insects and fungal diseases in corn.

Linoleic acid as corpse recognition signal in a social aphid

Social insect colonies constantly produce dead insects, which cause sanitary problems and potentially foster deadly pathogens and parasites. Hence, many social insects have evolved a variety of hygienic behaviors to remove cadavers from the colonies. To that end, they have to discriminate dead insects from live ones, where chemical cues should play important roles. In ants, bees and termites, such corpse recognition signals, also referred to as “death pheromones” or “necromones”, have been identified as fatty acids, specifically oleic acid and/or linoleic acid. Meanwhile, there has been no such report on social aphids. Here we attempted to identify the “death pheromone” of a gall-forming social aphid with second instar soldiers, Tuberaphis styraci, by making use of an artificial diet rearing system developed for this species. On the artificial diet plates, soldiers exhibited the typical cleaning behavior, pushing colony wastes with their heads continuously, against dead aphids but not against live aphids. GC-MS and GC-FID analyses revealed a remarkable increase of linoleic acid on the body surface of the dead aphids in comparison with the live aphids. When glass beads coated with either linoleic acid or body surface extract of the dead aphids were placed on the artificial diet plates, soldiers exhibited the cleaning behavior against the glass beads. A series of behavioral assays showed that (i) soldiers exhibit the cleaning behavior more frequently than non-soldiers, (ii) young soldiers perform the cleaning behavior more frequently than old soldiers, and (iii) the higher the concentration of linoleic acid is, the more active cleaning behavior is induced. Analysis of the lipids extracted from the aphids revealed that linoleic acid is mainly derived from phospholipids that constitute the cell membranes. In conclusion, we identified linoleic acid as the corpse recognition factor of the social aphid T. styraci. The commonality of the death pheromones across the divergent social insect groups (Hymenoptera, Blattodea and Hemiptera) highlights that these unsaturated fatty acids are generally produced by enzymatic autolysis of cell membranes after death and therefore amenable to utilization as a reliable signal of dead insects.

Mixture compatibility of Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) with pesticides used in soybean

ABSTRACT: Anticarsia gemmatalis (Hübner: 1818) (Lepidoptera: Erebidae) is one of the main pests that affect soybean crops, causing defoliation. In the vegetative stages, defoliation occurs together with weeds, and in the reproductive stages with pathogens. In this sense, to maintain plant health, it is necessary to carry out the combined use of pesticides. Thus, this research determined the compatibility of the entomopathogenic virus AgMNPV with the main herbicides and fungicides used in soy at different times of the mixture. The artificial diet was immersed in the solutions of the pesticides and their mixtures and supplied to A. gemmatalis caterpillars, immediately and after one and two hours of mixing. The evaluation was performed by quantifying the number of dead caterpillars by mixing the AgMNPV virus with herbicides and fungicides, even after two hours of mixing if compatible. The observed scenarios showed a compatibility of the virus with the herbicides and fungicides, with mortality rates between 70 to 99% for A. gemmatalis.

Comparison of Some Biological Parameters between Young Grass Carp, Ctenopharyngodon idella (Valenciennes, 1884) fed on Artificial Diet and Alfalfa inEarthen Ponds at Basrah, Iraq

The current study aims to compare the relationships of some biological parameters of young grass carp, Ctenopharyngodon idella (Valenciennes, 1844) fed on artificial diet and alfalfa in earthen ponds. These parameters included length-weight relationship, relative length and weight of the alimentary canal, condition factor and survival rate. Results of lengthweight relationship showed that no significant differences (P>0.05) were recorded for the t-test for the ideal value of 3 for fishes fed on artificial diet or alfalfa plant. The condition factor of young grass carp fed on artificial diet ranged between 0.021 to 1.074, while for fishes fed on alfalfa plant was 0.023 to 1.270 for allometric and Fulton’s condition factor, respectively. Also, there was no significant difference (P>0.05) for fishes fed on both diets in all biological parameters, the relative length of the alimentary canal for fishes fed on artificial diet (1.65) and on alfalfa plant (1.69), while the relative weight of the alimentary canal were 0.0285 and 0.0218 for fishes fed on both diets, respectively. Results also showed that the Zihler coefficient were 7.43 and 7.62, respectively. The survival rate was 100% for both treatments.

First Evidence of Feeding-Induced RNAi in Banana Weevil via Exogenous Application of dsRNA

Banana weevil (Cosmopolites sordidus) is the most devastating pest of banana and plantain worldwide, yet current control measures are neither effective, sustainable, nor environmentally sound, and no resistant farmer-preferred cultivars are known to date. In this paper, we examined the ability to induce RNA interference (RNAi) in the banana weevil via feeding. We first developed an agar- and banana corm (rhizome) flour-based artificial diet in a multi-well plate setup that allowed the banana weevils to complete their life cycle from egg through the larval instars to the pupal stage in an average period of 53 days. Adults emerged about 20 days later. The artificial diet allowed the tunneling and burrowing habits of the larvae and successful metamorphosis up to adult eclosion. Adding dsRNA for laccase2 to the artificial diet resulted in albino phenotypes, confirming gene-silencing. Finally, C. sordidus was fed with dsRNA against a selection of essential target genes: snf7, rps13, mad1, vha-a, vha-d, and lgl for a period of 45 days. 100% mortality within 9–16 days was realized with dssnf7, dsrps13, and dsmad1 at 200 ng/mL artificial diet, and this corresponded to a strong reduction in gene expression. Feeding the dsRNA targeting the two vha genes resulted in 100% mortality after about 3–4 weeks, while treatment with dslgl resulted in no mortality above the dsgfp-control and the water-control. Our results have implications for the development of RNAi approaches for managing important crop pests, in that banana weevils can be controlled based on the silencing of essential target genes as snf7, rps13, and mad1. They also highlight the need for research into the development of RNAi for banana protection, eventually the engineering of host-induced gene-silencing (HIGS) cultivars, given the high RNAi efficacy and its species-specific mode of action, adding the RNAi approach to the armory of integrated pest management (IPM).

Habituation to a Deterrent Plant Alkaloid Develops Faster in the Specialist Herbivore Helicoverpa assulta Than in Its Generalist Congener Helicoverpa armigera and Coincides with Taste Neuron Desensitisation

The two closely related moth species, Helicoverpa armigera and H. assulta differ strongly in their degree of host-plant specialism. In dual-choice leaf disk assays, caterpillars of the two species that had been reared on standard artificial diet were strongly deterred by the plant-derived alkaloid strychnine. However, caterpillars of both species reared on artificial diet containing strychnine from neonate to the 5th instar were insensitive to this compound. Fifth instar caterpillars of H. assulta and 4th or 5th instars of H. armigera not exposed to strychnine before were subjected to strychnine-containing diet for 24 h, 36 h, 48 h, or 72 h. Whereas H. assulta displayed habituation to strychnine after 48 h, it took until 72 h for H. armigera to become habituated. Electrophysiological tests revealed that a deterrent-sensitive neuron in the medial sensillum styloconicum of both species displayed significantly reduced sensitivity to strychnine that correlated with the onset of habituation. We conclude that the specialist H. assulta habituated faster to strychnine than the generalist H. armigera and hypothesis that desensitization of deterrent-sensitive neurons contributed to habituation.

Activity of Chloroformic Extract from Salvia connivens (Lamiales: Lamiaceae) and Its Principal Compounds against Spodoptera frugiperda (Lepidoptera: Noctuidae)

Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) is one of the most damaging pests in maize crops. In order to manage it, synthetic insecticides such as diamides, neonicotinoids, and pyrethroids are used, but they present a risk for humans and the environment. Investigations of safer alternatives include the use of natural extracts. Thus, this research evaluated the effects of chloroform extract (CHCl3Sc) (5000, 4000, 2000, 1000, and 500 ppm) on aerial parts of Salvia connivens and of nonanal and pyrocatechol (1000, 600, 400, and 80 ppm) on S. frugiperda mortality, duration of the larva and pupae phases, and pupae weight after 24 h. The second instars of S. frugiperda larvae were fed an artificial diet incorporating the extract and compounds. The CHCl3Sc had insecticidal activity against S. frugiperda, showing an LC50 of 1504 ppm. Insectistatic activity began at 1000 ppm, increasing pupal and larval duration in 7.6 and 1.4 days, respectively. Pyrocatechol and nonanal were found in this extract. The first did not have any significant difference in larval or pupal mortalities. On the other hand, insectistatic activity was shown at 500 ppm, increasing the larval duration by 1.7 days compared with the control. In the case of nonanal, the insecticide activity was LC50 of 200 ppm, and insectistatic activity started at 80 ppm, increasing larval duration by 3.2 days compared with the control and reducing pupal weight by 3.4%. The results show that chloroformic extract had insecticidal and insectistatic activities against S. frugiperda; nonanal was an aldehyde compound present in this extract, which confers insecticidal and insectistatic activities against this pest.

Performance of a Native Butterfly and Introduced Moth on Native and Introduced Lineages of Phragmites australis

This study examined the performance of Poanes viator (Edwards) (Hesperiidae), a native North American skipper, and Rhizedra lutosa (Hübner) (Noctuidae), an introduced moth, reared on native and non-native, invasive lineages of Phragmites australis. Poanes viator is a generalist on monocots and larvae were also fed leaves of Zizania aquatica, a native macrophyte that the skipper commonly uses as a host plant. Larval survival and duration, pupal weight, and pupation time were compared for P. viator feeding on leaf tissue and R. lutosa feeding on rhizomes of either native or introduced plants. We also tested an artificial diet supplemented with P. australis rhizome powder as a potential food for rearing other stalk and rhizome boring Lepidoptera. In experiments using excised plant tissues, some individuals of both species fed and developed to the pupal stage on native and introduced plants, but overall, larval survival rates were low. Plant species/haplotype identity did not cause strong differences in larval survival for either species. However, P. viator larvae only pupated when feeding on native plants (Zizania aquatica and native P. australis haplotypes), whereas R. lutosa successfully pupated on both native and introduced P. australis. Although larval survival was low, 100% of P. viator and 95% of R. lutosa that reached the pupal stage emerged as adults. Rhizedra lutosa larvae fed an artificial diet supplemented with P. australis rhizome powder had significantly greater survival and pupal weights, and shorter pupation times than larvae fed rhizomes only. Several specialist Lepidopteran species are being considered for approval as biological control agents for the non-native P. australis haplotype, and the convenience and increased larval performance make this artificial diet a good alternative for rearing organisms.