Effects of kinship or familiarity? Small thrips larvae experience lower predation risk only in groups of mixed-size siblings

In many species of insects, larvae are distributed in an aggregated fashion. As they may differ in size and size matters to predation risk, small larvae may be less likely to fall prey to predators when near large and therefore better-defended larvae. We hypothesize that the small larvae may profit even more when these large larvae are siblings. We tested this hypothesis on kinship-dependent survival in groups of larvae of the Western flower thrips (Frankliniella occidentalis) exposed to a predatory mite (Iphiseius degenerans). Our experiments showed that small larvae in sibling groups survive significantly better than in non-sibling groups, but only when such groups consisted of a mixture of small and large larvae. To test whether the survival effect we found is due to familiarity of thrips larvae growing up together (i.e. on one leaf), we also measured survival in sibling groups of larvae grown up on different leaves and in non-sibling groups of larvae grown up on the same leaf. These experiments showed an increased survival of small thrips larvae only in groups of sibling larvae from the same leaf. Non-sibling larvae did not show an increased survival when they come from the same leaf. Our results indicated that the increased survival in sibling groups was only partly due to the familiarity effect we tested. Growing up together did not return the same survival effect for non-siblings as it did for siblings. We conclude that growing up together is a necessary but not sufficient condition for discrimination in thrips larvae

Predatory mite attraction to herbivore-induced plant odors is not a consequence of attraction to individual herbivore-induced plant volatiles

Predatory mites locate herbivorous mites, their prey, by the aid of herbivore-induced plant volatiles (HIPV). These HIPV differ with plant and/or herbivore species, and it is not well understood how predators cope with this variation. We hypothesized that predators are attracted to specific compounds in HIPV, and that they can identify these compounds in odor mixtures not previously experienced. To test this, we assessed the olfactory response of Phytoseiulus persimilis, a predatory mite that preys on the highly polyphagous herbivore Tetranychus urticae. The responses of the predatory mite to a dilution series of each of 30 structurally different compounds were tested. They mites responded to most of these compounds, but usually in an aversive way. Individual HIPV were no more attractive (or less repellent) than out-group compounds, i.e., volatiles not induced in plants fed upon by spider-mites. Only three samples were significantly attractive to the mites: octan-1-ol, not involved in indirect defense, and cis-3-hexen-1-ol and methyl salicylate, which are both induced by herbivory, but not specific for the herbivore that infests the plant. Attraction to individual compounds was low compared to the full HIPV blend from Lima bean. These results indicate that individual HIPV have no a priori meaning to the mites. Hence, there is no reason why they could profit from an ability to identify individual compounds in odor mixtures. Subsequent experiments confirmed that naive predatory mites do not prefer tomato HIPV, which included the attractive compound methyl salicylate, over the odor of an uninfested bean. However, upon associating each of these odors with food over a period of 15 min, both are preferred. The memory to this association wanes within 24 hr. We conclude that P. persimilis possesses a limited ability to identify individual spider mite-induced plant volatiles in odor mixtures. We suggest that predatory mites instead learn to respond to prey-associated mixtures of volatiles and, thus, to odor blends as a whole

Vismonitoring Zoete Rijkswateren en Overgangswateren t/m 2019 : Deel II, Toegepaste methoden

Om een inschatting te krijgen van de toestand van de zoete rijkwateren en overgangswateren worden diverse vismonitoringsprogramma’s uitgevoerd. Deze programma’s maken deel uit van het Wettelijke Onderzoekstaken (WOT) programma in opdracht van het ministerie van Landbouw, Natuur en Voedselkwaliteit (LNV) en het Programmaplan Vis-en Biotamonitoring 2018-2023 van Rijkswaterstaat (RWS). In totaal worden 13 monitoringsprogramma’s en één registratieprogramma in de grote zoete rijkswateren (meren en rivieren), de overgangswateren en de spuikom bij Kornwerderzand in de Waddenzee uitgevoerd. Ontsluiting van vismonitoringsgegevens gebeurt op drie manieren. Het voorliggende rapport (Deel II) is een achtergronddocument waarin de gebruikte monitoringsmethodieken in de verschillende vismonitoringen in de zoete rijkswateren en overgangswateren t/m 2019 worden vastgelegd. In het rapport ‘Toestand en trends’ (Deel I) worden de resultaten geïnterpreteerd (trends en duiding). Daarnaast worden de monitoringsdata via een dataportaal1 ontsloten (voorheen rapportage Deel III). Wijzigingen die in 2019 zijn doorgevoerd, staan puntsgewijs opgesomd in paragraaf 1.1. De veranderingen betreffen het beëindigen van bepaalde bemonsteringen of juist het starten van nieuwe bemonsteringen, maar ook veranderingen in monsterlocaties of –frequenties en rapportage

Vismonitoring Zoete Rijkswateren en Overgangswateren t/m 2018 : Deel II: Toegepaste methoden

Om een inschatting te krijgen van de kwaliteit van de zoete rijkwateren en overgangswateren, wordt het vismonitoringprogramma uitgevoerd. Dit programma maakt deel uit van het Programmaplan Vis-en Biotamonitoring 2018-2023 van Rijkswaterstaat en het Wettelijke Onderzoekstaken (WOT) programma in opdracht van het ministerie van Landbouw, Natuur en Voedselkwaliteit (LNV). Het programma bestaat uit 13 monitoringsprogramma’s en één registratieprogramma in de grote zoete rijkswateren (meren en rivieren) en overgangswateren en in de spuikom bij Kornwerderzand in de Waddenzee. Ontsluiting van vismonitoringsgegevens gebeurt op drie manieren: Deel I ‘Toestand en trends’ waarin de resultaten worden geïnterpreteerd (trends en duiding), het hier voorliggende rapport (Deel II) is een achtergronddocument waarin de gebruikte monitoringsmethodieken in de verschillende vismonitoringen in de zoete rijkswateren en overgangswateren t/m 2018 worden vastgelegd. Daarnaast worden de monitoringsdata via het dataportal1 ontsloten, voorheen heette dat Deel III. Wijzigingen die in 2018 zijn doorgevoerd, staan puntsgewijs opgesomd in paragraaf 1.1. De veranderingen betreffen het beëindigen van bepaalde bemonsteringen of juist het starten van nieuwe bemonsteringen, maar ook veranderingen in monsterlocaties of –frequenties en rapportage

Context‐dependent chemical communication: Alarm pheromones of thrips larvae

Thrips have several advantages that make them particularly suitable for the study of the evolution of alarm signalling. When in danger, thrips larvae defend themselves by the excretion of ‘anal droplets’: a predator touched by such a droplet interrupts the attack and switches to cleaning. These droplets may contain an alarm pheromone, consisting of two compounds: decyl acetate and dodecyl actetate. The presence of alarm pheromone evokes anti‐predator behaviour in thrips, such as elevated alertness and moving away from the scene, and this behaviour potentially improves the chances of survival of the signal receivers. Thrips larvae may encounter a range of predators, the one more dangerous than the other. If a thrips larva survives the presence of a predator, this larva may become a signal sender on a next occasion. Thrips live in groups, comprising both related and unrelated individuals. A practical advantage of the alarm pheromone of thrips is that synthetic mimics of its two components are available. The anal droplets can be observed, counted, collected and analysed for the presence and composition of pheromone. Furthermore, thrips larvae can be stimulated to produce droplets by prodding them with a fine brush. The combination of these advantages enables the manipulation of pheromone production as well as the determination of quality and quantity of the alarm pheromone in presence of various types of predator. Three main questions are central to this thesis. First, does the alarm pheromone of thrips larvae indeed improve the defensive capacities of conspecific thrips? Second, is thrips alarm pheromone production context‐dependent? And third, how does relatedness influence alarm communication