Plant quality or quantity? Host exploitation strategies in three Chrysomelidae species associated with Asteraceae host plants

Abstract

Phytophagous insects which feed on the leaves of herbaceous host plants have to adapt their life histories to the fact that protein nitrogen is usually highest in growing tissues in spring. We monitored field populations of larvae and adults of three chrysomelid species (Galeruca tanaceti (L.) (main host Achillea millefolium (L.) Yarrow), Cassida rubiginosa (Mueller) (main host Cirsium arvense (L.) Scop.) and Oreina luctuosa (Suffrian) (host Centaurea scabiosa (L.)) together with the amount of protein nitrogen of their food resources and host plant biomass. As expected, the development of host quality, measured as concentration of protein nitrogen, and host plant biomass showed inverse trends during the season. The euryphagous G. tanaceti attacks Achillea early and profits from high nitrogen concentrations in the leaves. Occasional overexploitations of local populations of Achillea are compensated by the capacity to move to other host species. In C. rubiginosa, a species with a host range restricted to the Cardueae, the main larval feeding activity is postponed to a period when the nitrogen content of the host leaves had dropped to 50% of its initial value, but when host plant biomass had increased by 30%. In the monophagous O. luctuosa the larval development is synchronized with a still later phase of host phenology, at which the nitrogen content is below 50% but plant biomass has reached its maximum. There seem to be selection factors, which oppose the use of high quality food in spring and which force the latter two species to postpone their larval development to a later time in the year. This could be caused by numerous factors like, for example, mean daytime temperature. Later in the season the larvae have to cope with the low quality of their host plants. They have, however, the advantage of large quantities of food available.A laboratory study with adults and mature larvae of O. luctuosa shows that this species can overcome low levels of protein nitrogen either by selecting younger leaves with higher nitrogen concentrations or by increasing the daily food consumption rate (RCR) on leaves with a low level of nitrogen and by a prolongation of the feeding period. In this way the larvae compensate the effect of lower daily growth rates (RGR) and a lower food conversion index (ECI) on poor food quality: Regardless of the level of protein nitrogen there was no statistically significant difference in total gain of weight during the third-instar feeding period and in the weight at the end of the third larval stage. The three investigated chrysomelids show that there exists a broad spectrum of adaptations to overcome the dilemma of variable food quality.

How far away is the next basket of eggs? Spatial memory and perceived cues shape aggregation patterns in a leaf beetle

“…Two behavioral components lead to larval aggregation. The first is the choice of where to place the eggs within the landscape (Heisswolf et al 2006) or plant (Whitham 1978, Silva andFurlong 2012), and can be modulated by predators/parasitoids (Higashiura 1989), the availability and quality of host plants (Obermaier and Zwo¨lfer 1999), and vegetation structure (Meiners and Obermaier 2004). Information about conspecific egg presence might also influence the oviposition choice, but this phenomenon has not been sufficiently investigated.…”

Herbivore Larval Development at Low Springtime Temperatures: The Importance of Short Periods of Heating in the Field

“…Many insects prefer young plants or tissues to old ones and are therefore restricted to feeding at certain times of the season [2]. These herbivores may profit by a fast development and high pupal weight due to the readily assimilated nitrogen at this time of the year [3]. On the other hand, at least in Palaearctic regions, herbivores which appear early in the season are vulnerable to low mean and minimum daily temperatures, which might often drop below the lower developmental threshold of the species in question and severely reduce growth and development.…”

“…While the adult beetles die, the eggs are the overwintering form. Between March and April, at cold springtime temperatures, the larvae emerge and develop while feeding on the first young leaves of their host plants [3]. After approximately four weeks of feeding, the larvae pupate after the fourth larval stage, in the soil.…”

Opposing survivorship and fecundity effects of host phenology on the gall‐forming aphid Hormaphis hamamelidis

“…Synchronisation can be at a fine scale: insect egg hatch can be synchronised with budbreak of individual trees (Vandongen et al, 1997;Mopper et al, 2000). Frequently, there are trade-offs between insect survival and performance based on the timing of host and insect phenologies (Dixon, 1976;Fay & Whitham, 1990;Ozaki, 1998;Obermaier & Zwolfer, 1999;Rossi et al, 1999;Tikkanen et al, 1999). In general, herbivores that hatch and=or start feeding earlier enjoy enhanced reproductive performance but suffer higher mortality.…”