The distribution of herbivores between leaves matches their performance only in the absence of competitors

Abstract

Few studies have tested how plant quality and the presence of competitors interact in determining how herbivores choose between different leaves within a plant. We investigated this in two herbivorous spider mites sharing tomato plants: Tetranychus urticae , which generally induces plant defenses, and Tetranychus evansi , which suppresses them, creating asymmetrical effects on coinfesting competitors. On uninfested plants, both herbivore species preferred young leaves, coinciding with increased mite performance. On plants with heterospecifics, the mites did not prefer leaves on which they had a better performance. In particular, T. urticae avoided leaves infested with T. evansi , which is in agreement with T. urticae being outcompeted by T. evansi . In contrast, T. evansi did not avoid leaves with the other species, but distributed itself evenly over plants infested with heterospecifics. We hypothesize that this behavior of T. evansi may prevent further spread of T. urticae over the shared plant. Our results indicate that leaf age determines within‐plant distribution of herbivores only in absence of competitors. Moreover, they show that this distribution depends on the order of arrival of competitors and on their effects on each other, with herbivores showing differences in behavior within the plant as a possible response to the outcome of those interactions.

A sink host allows a specialist herbivore to persist in a seasonal source

“…The likelihood of such evolutionary rescue increases with the amount of standing genetic variation available for adaptation to the sink environment [ 15 , 66 , 67 ]. The WCM population we used to test adaptation to brome was established from a large number of individuals collected at several distant geographical locations, a procedure that is likely to maximize genetic variance [ 53 ]. By following this method, we ensured a much larger level of genetic variation than that usually found in populations used in most studies of experimental evolution, which have shown adaptation to a given environment [ 19 , 68 , 69 ].…”

“…Indeed, there is ample evidence that herbivorous mites use different types of cues upon which they base their decision to undertake aerial dispersal [ 50 , 51 ]. Moreover, they are also ambulatory dispersers, using cues to move from or towards patches [ 52 , 53 ]. Here, we evaluate these two types of dispersal in WCM exposed to wheat or brome.…”

Intraspecific interaction of host plant influences local distribution of specialist herbivores through metabolic alterations in leaves

“…Another possible reason why the findings did not support our hypothesis is the effects of resource competition among herbivores. In some cases, resource competition among herbivores influences herbivore distribution (e.g., Suzuki 1986;Schoonhoven et al, 2005;Godinho et al, 2020). A previous study pointed out that G. grisescens is vulnerable to resource competition from G. atrocyanea (Suzuki, 1986).…”

Specific sequence of arrival promotes coexistence via spatial niche preemption by the weak competitor

“…All experiments were performed with outbred populations of T. urticae and T. evansi spider mites, formed via controlled crosses among four T. evansi and three T. urticae populations collected in different locations in Portugal (Godinho et al 2020b). Before the experiment, spider mite populations were maintained in boxes containing leaves detached from five-week-old tomato plants (Solanum lycopersicum, var MoneyMaker), with their petiole in a small pot containing water, under controlled conditions (25 ºC, 68% of humidity, photoperiod of 16 hours light/8 hours dark).…”