Parsing handling time into its components: implications for responses to a temperature gradient.

The functional response is a key element of predator-prey interactions, and variations in its parameters influence interaction strength and population dynamics. Recent studies have used the equation of the metabolic theory of ecology (MTE) to quantify the effect of temperature on the parameter Th, called "handling time," and then predict the responses of predators and communities to climate change. However, our understanding of the processes behind Th and how they vary with temperature remains limited. Using a ladybeetle-aphid system, we compared estimates of Th to direct observations of handling time across a temperature gradient. We found estimated Th values to be greater than observed Th values, suggesting that predation rate is not limited by the time available for handling prey. We next estimated the corrected digestion time, i.e., digestion time corrected for gut capacity, by subtracting observed to estimated Th values. We finally plotted the relationships between temperature and handling or digestion rates. As predicted by MTE, the corrected digestion rate increased exponentially with warming whereas, in contrast to MTE prediction, the relationship between handling rate and temperature was hump shaped. The parameter Th is thus confusing because it combines handling and digestive processes that have different thermal responses. This may explain why general patterns in the relationship between Th and temperature have been difficult to identify in previous studies.

The effect of relatedness on the response of Adalia bipunctata L. to oviposition deterring cues.

Larvae of aphidophagous ladybirds leave a cue in their tracks that deters oviposition. The influence of relatedness on this behaviour is for the first time explored in this paper. Two-spot ladybird females (Adalia bipunctata L.) under different conditions (young and naive, young and experienced, and old and naive) were exposed either to (i) clean filter paper, (ii) filter paper contaminated with unrelated larval tracks or (iii) filter paper contaminated with related larval tracks from their offspring. Oviposition time was recorded during nine hours. Oviposition was inhibited by larval tracks, and was more so by related than unrelated ones. Experienced females showed the same behaviour but with lower intensity. With old females, response was not significant with any type of larval tracks. This is the first report of the effect of relatedness on a ladybird's response to larval tracks.

Phylogeny of ladybirds (Coleoptera: Coccinellidae): are the subfamilies monophyletic?

The Coccinellidae (ladybirds) is a highly speciose family of the Coleoptera. Ladybirds are well known because of their use as biocontrol agents, and are the subject of many ecological studies. However, little is known about phylogenetic relationships of the Coccinellidae, and a precise evolutionary framework is needed for the family. This paper provides the first phylogenetic reconstruction of the relationships within the Coccinellidae based on analysis of five genes: the 18S and 28S rRNA nuclear genes and the mitochondrial 12S, 16S rRNA and cytochrome oxidase subunit I (COI) genes. The phylogenetic relationships of 67 terminal taxa, representative of all the subfamilies of the Coccinellidae (61 species, 37 genera), and relevant outgroups, were reconstructed using multiple approaches, including Bayesian inference with partitioning strategies. The recovered phylogenies are congruent and show that the Coccinellinae is monophyletic but the Coccidulinae, Epilachninae, Scymninae and Chilocorinae are paraphyletic. The tribe Chilocorini is identified as the sister-group of the Coccinellinae for the first time.

Assessment of patch quality by ladybirds: role of larval tracks.

Gravid females of the two-spot ladybird, Adalia bipunctata (L.), were deterred from ovipositing when kept in petri dishes that had previously contained conspecific larvae but not conspecific adults, or the larvae of another two species of ladybird, Adalia decempunctata (L.) and Coccinella septempunctata L. The deterrent effect was density dependent and mediated via a chloroform-soluble contact pheromone present in the larval tracks. Similarly, gravid females of C. septempunctata were deterred from ovipositing by conspecific larval tracks and chloroform extracts of these tracks, but not by the tracks or extracts of tracks of A. bipunctata larvae. That is, in ladybirds the larvae produce a species-specific oviposition-deterring pheromone. In the field, the incidence of egg cannibalism in ladybirds increases very rapidly with the density of conspecific eggs or larvae per unit area. Thus, in responding to the species specific oviposition deterring pheromone female ladybirds reduce the risk of their eggs being eaten and spread their offspring more equally between patches.

Attack strategy of ladybird beetles (Coccinellidae): factors shaping their numerical response.

Temporal changes in aphid abundance pose a considerable challenge to ovipositing aphidophagous ladybirds, as in order to maximize their fitness they need to synchronize their reproduction with the early development of aphid populations. Field census data and laboratory experiments were used to determine how ovipositing females of the two-spot ladybird, Adalia bipunctata (L.), assess whether an aphid population is suitable for exploitation. In the field, two-spot ladybirds usually laid eggs well before aphid populations peaked in abundance. In the laboratory they showed a marked reduction in their reproductive numerical response in the presence of larvae of their own species but not of other aphidophagous ladybirds. At the highest aphid density this was not a consequence of competition for food between larvae and ovipositing females. In the presence of conspecific larvae gravid females were very active and as a consequence more likely to leave an area, and when confined with other conspecific females or larvae laid fewer eggs and later than females kept on their own. The extent of the inhibition of egg laying is negatively correlated with the rate of encounter with larvae. Thus it is proposed that gravid females appear mainly to use the presence of conspecific larvae to assess the potential of an aphid colony for supporting the development of their offspring.