The role of leaf cellulose content in determining host plant preferences of three defoliating insects present in the Andean‐Patagonian forest

Abstract

Phytophagous insects choose their feeding resources according to their own requirements in addition to properties of the host plants, such as biomechanical defences. The feeding preferences of the native folivorous insects of the Andean-Patagonian forest (Argentina) have rarely been studied. These environments present a wide diversity and abundance of insects associated with trees of the Nothofagus and Lophozonia (Nothofagaceae) genera, which represent the main tree species of the forests of the southern hemisphere. In particular, Lophozonia alpina and Lophozonia obliqua are of great interest because they have a wide distribution, a high capacity for hybridization and exhibit great phenotypic plasticity. This versatility causes substantial variation in the biomechanical properties of leaves, affecting the feeding preferences of insects. The purpose of this work was to study the food selection behaviour of three leaf-chewing insects (Polydrusus nothofagii, Polydrusus roseaus (Coleoptera: Curculionidae) and Perzelia arda (Lepidoptera: Oecophoridae)) associated with L. alpina and L. obliqua as host plants. Based on their choices, our aim was to determine a preference scale for each insect species and the variables on which these preferences were based. Therefore, we selected trees of L. alpina and L. obliqua, measured several properties such as cellulose content and recorded which leaves were eaten. As a result, we determined that the three species of insects feed on both host plants but prefer the leaves of L. obliqua, with cellulose content being the main determining factor for their decisions. However, in the case of P. arda, there was a positive relationship between cellulose and host plant preference, whereas there was an opposite relationship for the weevils. We conclude that during feeding selection, there are some properties of the leaves that have a more important role than others and that the same property does not exert the same behavioural response in all folivorous insects.

Foraging behaviour of the exotic waspVespula germanica(Hymenoptera: Vespidae) on a native caterpillar defoliator

“…In addition, three control treatments were performed (nothing = empty box vs. Larvae ( n = 30), nothing vs. leaves without larval traces ( n = 27) and nothing vs. leaves with larval traces ( n = 18)). Because P. arda larvae tend to cluster in natural conditions, we offered as a stimulus five larvae simultaneously (Pietrantuono et al , 2017). Five entire mature leaves of similar size were used for the leaf stimulus.…”

“…First, we performed a Wilcoxon matched pair test (Bonferroni corrected) to determine whether there were differences between treatments and second we developed a model using a Bayesian approach to establish a scale of preferences between stimuli. This procedure provides a more straightforward way to determine the degree of attraction between stimuli and it is widely used by ecologists in animal behaviour studies (Ellison, 2004; McNamara et al , 2006; Valone, 2006; Pereira et al , 2013; Pietrantuono et al , 2014, 2015, 2017).…”

“…In addition, the units of this scale were expressed in terms of the standard deviations of the discriminal dispersion of the reference stimulus. Thus, the preference for each stimulus within the scale was positioned relative to this value, and its values were expressed in terms of the discriminal dispersion (Pietrantuono et al , 2017).…”

“…They produce silk for quick escape and for leaf tying when they build their shelter. When these caterpillars detect the presence of a threat, they leave this shelter, leaving traces of silk and faeces within, and build a new one (Pietrantuono et al , 2017). Therefore, we suppose that olfactory cues are essential for V. germanica during foraging of P. arda prey, as the wasps cannot observe the presence of the larva because they are hidden in the shelter made of leaves.…”

Host plant choice and effect of temperature on feeding behaviour of Perzelia arda (Lepidoptera: Depressariidae), a leaf‐tying larva, on Nothofagaceae from the Andean Patagonian forest

“…Herbivorous insects are not passive consumers and may modify their feeding behaviour according to their host plant foliar traits (e.g. nutritional quality, chemical and physical defences, water content) and environmental context (Hanson 1983;Schoonhoven et al 2005;Hong et al 2012;Pietrantuono et al 2017). Global changes in environment affect biodiversity in all biomes (Sala et al 2000).…”