Negative interactions between spider mites and aphids mediated by feeding behaviour and honeydew

CÉDOLA, CLAUDIA C.; SALAS GERVASSIO N.G

Ciudad de Recife, Brasil

Congreso; XIII International Congress of Acarology; 2010

One of the most important issues in ecology is tounderstand the causal mechanisms that structuresand shapes ecological comrnunities. Insectherbivores induce a wide variety of trait changes inplants. They are -specialized for using particulartissues of the plants and the quality of resourceswithin and among plants is highly variable. There ismuch research focused on direct trophic interactions(prey-predators and host-parasitoids) but thepotential of non tropic, indirect and facilitativeinteractions has been ignored. It is possible forguilds of phytophagous insects that one guild altersthe chemistry or the morphology of plants for otheror later guilds. So, under low herbivory conditions,early feeding gui1ds could affect the population´sdynamics and the community organization for laterfeeders. Among the herbivore arthropods that feedon strawberry the main pest is Tetranychus urticaeKoch (Acari: Tetranychidae) and also severalspecies of aphids such as Aphis gossypii Glover,Aphis fabae Scopoli, Myzus persicae (Sulzer),Macrosiphum euphorbiae Thomas andChaetosiphon fragaefolli Cockerell. Both guildscoexist, especial1y during autumn and spring, andfeed on undersides of strawberry leaflets. However,well-developed colonies of both groups are notusual in field. Our hypothesis 1S tbat there existnegative interactions between spider mites andaphids. To test this hypothesis spatial coincidence infield between both herbivores was analyzed usingGriffith Index (le). Also under controlled conditionsof temperature, humidity and light (25±1 °C, 60-70% and 14:10, respectively) were analyzed: 1) therate of increase of T. urticae and C. fragaefolli atdensities 20:0 - 10:10 and 0:20 individuals/leaflet(n= 20 for each treatment), respective1y, 2) theeffect of honeydew on T. urticae preference and 3)the effect of strawberry leaflets previously damagedon C. fragaefolli preference (n = 15 for eachtreatment). Data were analyzed with ANOVA andKruskal-Wallis. le was low (O - 0.3) when thepercentage of infested leaflets by spider mites was25%, GI was variable (0-1) between 25% and 50%and up 50% spatial coincidence becomes complete.The rate increase of T. urticae diminished due to theC. fragaefolli interaction. The rate increase of C.fragaefolli did not change due to the spider mitesinteraction but a migratory behaviour to the upperside of leaflet was observed. Strawberry discs withhoneydew and leaf damage by T. urticae was 110tpreferred by T. urticae and C. fragaefolli,respectively. In this work, the negative interactionbetween these guilds could be attributed to somerepellent compound in aphid honeydew and bytissue disorder due to spider mites. Changes inducedby one of these herbivores reduce the resourceavailability for the other one. This results in atendency to avoid each other.