Silicon dioxide in the defence induction of soybean against Spodoptera frugiperda

Silicon can increase the natural defence of plants against stresses including herbivorous insects. Silicon dioxide (SiO₂) is one of the forms of silicon, and despite its wide use in the industrial sector, its use in agriculture is still poorly adopted. The aim of this study was to evaluate the effectiveness of foliar application of SiO₂ in inducing defence against Spodoptera frugiperda in soybean. The experiments were conducted in a completely randomised design with four treatments (0%, 1%, 2.5%, and 5% of SiO₂). The effect on cannibalism, biological parameters (mortality, duration of the larval stage, duration of the pupal stage and pupal weight) and wear on the mandible of S. frugiperda were evaluated. The foliar silicon content was also determined. The supply of SiO₂ prolonged the duration of the larval and pupal stages of the S. frugiperda by 0.56 and 0.17 days for each 1% of SiO₂ applied, respectively. The use of SiO₂ at 5% increased the mortality rate of caterpillars in the larval stage by approximately 25%. There was no effect of SiO₂ application on cannibalism and weight of S. frugiperda pupae. There was wear on the caterpillars' jaws in the third and fourth instar at the highest SiO₂ concentration. The application of SiO₂ promoted greater accumulation of silicon in soybean leaves. It is concluded that the foliar application of SiO₂ affects the biological performance of S. frugiperda through the induction of defence in the soybean crop and presents itself as a promising strategy in integrated pest management programmes.     

Host plant trichomes and the advantage of being big: progeny size variation of the pipevine swallowtail

1. Plants possess numerous traits that confer resistance against insect herbivores, and herbivores, in turn, can evolve traits to ameliorate the effectiveness of these traits. The pipevine swallowtail, Battus philenor, is an extreme specialist on plants in the genus Aristolochia. The only host plant available to the California population of B. philenor is A. californica. Aristolochia californica is distinct from most other B. philenor host plants in that it is pubescent. 2. The progeny of B. philenor are larger in California compared with populations examined in Texas. Size differences persist throughout larval development. 3. Regardless of maternal host plant, population differences in progeny size persist, and crosses between California (large progeny) and Texas (small progeny) B. philenor populations resulted in offspring producing intermediate sized progeny, indicating a heritable component to progeny size variation. 4. California neonate caterpillars more easily overcame the trichomes of A. californica compared with Texas neonates. When trichomes were removed from A. californica, time to feeding establishment was reduced for caterpillars from both populations. Texas caterpillars established feeding sites on A. californica with trichomes removed, in the same time required to establish feeding on their non‐pubescent host plant, A. erecta. 5. This study shows that plant trichomes might impose selection pressure on progeny size.     

Inactivation of the ecdysteroid UDP-glucosyltransferase (egt) gene of Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) improves its virulence towards its insect host

Some baculovirus have been genetically modified for the inactivation of their ecdysteroid glucosyltransferase (egt) gene, and these viruses were shown to kill infected larvae more rapidly when compared to wild-type virus infections. We have previously identified, cloned, and sequenced the egt gene of Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV). Here we present data regarding the construction of an egt minus (egt−) AgMNPV and its virulence towards its insect host. We have inserted an hsp70-lacZ (3.7 kb) gene cassette into the egt gene open reading frame (ORF) and purified a recombinant AgMNPV (vAgEGTΔ-lacZ). Bioassays with third-instar A. gemmatalis larvae showed that viral occlusion body (OB) production were consistently lower from infections with vAgEGTΔ-lacZ compared to the wild-type virus. A mean of 20.4×10⁸ OBs/g/larva and 40.7×10⁸ OBs/g/larva was produced from vAgEGTΔ-lacZ and AgMNPV infections, respectively. The mean lethal concentration which killed 50% of insects in a treatment group (LC₅₀) for the 10th day after virus treatment (DAT) was 3.9-fold higher for the wild-type virus compared to vAgEGTΔ-lacZ. The recombinant virus killed A. gemmatalis larvae significantly faster (ca. 1–2.8 days), than the wild-type AgMNPV. Therefore, the vAgEGTΔ-lacZ was more efficacious for the control of A. gemmatalis larvae (in bioassays) compared to wild-type AgMNPV.     

Fruit abscission by Physalis species as defense against frugivory

Fruit abscission as a response to herbivory is well-documented in many plant species, but its effect on further damage by mobile herbivores that survive fruit abscission is relatively unstudied. Physalis plants (Solanaceae) abscise fruit containing feeding larvae of their main frugivore, Heliothis subflexa Guenée (Lepidoptera: Noctuidae), a specialist moth. We tested the ability of H. subflexa larvae placed under the plant canopy to find and climb onto two architecturally different Physalis species. Physalis pubescens L., a low, shrub-like, spreading plant, abscises its fruit at a higher rate than Physalis angulata L., a tall arborescent plant. As a result, small larvae are more often dropped from P. pubescens . Third and fifth instars located P. pubescens faster and with a higher probability than P. angulata . Although fifth instars outperformed third-instar caterpillars at finding P. angulata , P. pubescens was located equally fast by the two instars. Heliothis subflexa located Physalis plants more successfully and more quickly than a close relative, the generalist Heliothis virescens Fabricius. The higher fruit abscission rates in P. pubescens may be an evolved response to its greater susceptibility to searching caterpillars.     

一种测定鳞翅目幼虫取食选择的方法——叶碟法及其改进和注意事项

叶碟法是鳞翅目幼虫取食选择实验常用的一个方法。文章以经典的Jermy叶碟法为基础,介绍对其的改进以及实验中应该注意的事项,如幼虫的选择、幼虫取食的持续时间、叶碟的数目以及叶碟面积的测量等。     

Multi‐surveyor capture‐mark‐recapture as a powerful tool for butterfly population monitoring in the pre‐imaginal stage

For many elusive insect species, which are difficult to cover by standard monitoring schemes, innovative survey methods are needed to gain robust data on abundance and population trends. We suggest a monitoring of overwintering larvae for the endangered nymphalid butterfly Limenitis reducta. We tested different removal and capture‐mark‐recapture (CMR) approaches in a field study in the “Alb‐Donau” region, Germany. Classical removal and CMR studies require movement of the organisms under study, but in our approach, we replaced movement of the study organisms by random movement of multiple different surveyors. We tested the validity of the approach by comparing detection frequencies from our field data with simulated detections. Our results indicate that multi‐surveyor removal/CMR techniques are suitable for estimating abundance of overwintering L. reducta larvae. Depending on surveyor experience, the average detection probability ranged between 16% for novices and 35% for experts. The uncertainty of population estimates increased with a decrease in personnel expenditure. Estimated larval densities on a spruce clear‐cut varied between one and three individuals per 100 m², probably related to habitat conditions. We suggest a CMR approach with three to four trained surveyors for the monitoring of L. reducta populations in the overwintering stage. Compared with previous sampling methods, our approach is a powerful tool with clear advantages: long survey period, estimates of the absolute population size accompanied by uncertainty measures, and estimates of overwinter mortality. The proposed method can be adapted and used for several different butterfly species, other insect taxa with specific immobile life stages, and some sessile organisms, for example, elusive plants, fungi, or corals.