Jean-Louis Hemptinne

Effects of augmentative releases of eggs and larvae of the ladybird beetle, Adalia bipunctata, on the abundance of the rosy apple aphid, Dysaphis plantaginea, in organic apple orchards

The impact of augmentative releases of larvae and eggs of the indigenous ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) against the rosy apple aphid Dysaphis plantaginea Pass. (Homoptera: Aphididae), a major pest insect on apple trees, was assessed in field experiments in Switzerland, during 1997. In a first experiment, eggs and larvae were released on 3‐year old apple trees infested with five aphids at four different predator‐prey ratios (0:5, 1:5, 1:1, 5:1). In a second experiment, eggs and larvae were released at a predator‐prey ratio of 5:1 on branches of apple trees naturally infested with aphids. In both experiments, the interaction with ants was taken into account and the releases were done at two different times in spring. The results showed that an augmentative release of larvae significantly prevented the build‐up of colonies of D. plantaginea. Significant reductions in aphid numbers were recorded at the two highest predator‐prey ratios, 1:1 and 5:1. Larvae were efficient just before flowering of apple trees at a time when growers normally have to spray their trees. On trees where ants were present the larvae of A. bipunctata were significantly less efficient. Effects of eggs of A. bipunctata, however, were less reliable. At the first date of release (5 April), they did not hatch, probably as a consequence of bad weather conditions.

Interactions between ants and aphidophagous and coccidophagous ladybirds

Aphidophagous and coccidophagous coccinellids come into conflict with homopteran-tending ants for access to food. Antagonistic interactions between coccinellids and ants may be competitive or non-competitive. Competitive interactions occur when coccinellids attack aphids or coccids that are being tended by ants for honeydew. Non-competitive interactions include all interactions away from ant-tended homopteran colonies. We here review observations and studies of such interactions. We note that most competitive interactions occur at times when untended aphids/coccids are scarce. We describe the chemical and physical defences that coccinellids use against ant aggression and consider whether these have evolved as general anti-predator deterrents or specifically in response to ants. Myrmecophilous coccinellids are then considered, with particular focus on the two most studied species, Coccinella magnifica and Platynaspis luteorubra. We note that the myrmecophily of the two species has the same adaptive rationale—to enable the ladybirds to prey on ant-tended aphids at times of aphid scarcity—but that it is based on different traits to facilitate life with ants. Finally, we consider the role of ants in the evolution of habitat specialisation in some coccinellids.

Age and experience influence patch assessment for oviposition by an insect predator

Abstract.  1. Dynamic models of optimal foraging predict that an animals decision to accept or reject a patch depends not only on the environment and patch quality, but also on its internal state. Previous experiments have shown that the two‐spot ladybird beetle, Adalia bipunctata (L.), is reluctant to lay eggs in a patch of prey contaminated by the oviposition‐deterring pheromone produced by conspecific larvae.

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.

Using functional response modeling to investigate the effect of temperature on predator feeding rate and energetic efficiency

Temperature is one of the most important environmental parameters influencing all the biological processes and functions of poikilothermic organisms. Although extensive research has been carried out to evaluate the effects of temperature on animal life histories and to determine the upper and lower temperature thresholds as well as the optimal temperatures for survival, development, and reproduction, few studies have investigated links between thermal window, metabolism, and trophic interactions such as predation. We developed models and conducted laboratory experiments to investigate how temperature influences predator–prey interaction strengths (i.e., functional response) using a ladybeetle larva feeding on aphid prey. As predicted by the metabolic theory of ecology, we found that handling time exponentially decreases with warming, but—in contrast with this theory—search rate follows a hump-shaped relationship with temperature. An examination of the model reveals that temperature thresholds for predation depend mainly on search rate, suggesting that predation rate is primarily determined by searching activities and secondly by prey handling. In contrast with prior studies, our model shows that per capita short-term predator–prey interaction strengths and predator energetic efficiency (per capita feeding rate relative to metabolism) generally increase with temperature, reach an optimum, and then decrease at higher temperatures. We conclude that integrating the concept of thermal windows in short- and long-term ecological studies would lead to a better understanding of predator–prey population dynamics at thermal limits and allow better predictions of global warming effects on natural ecosystems.

BODY SIZE DISTRIBUTION IN PREDATORY LADYBIRD BEETLES REFLECTS THAT OF THEIR PREY

The size distribution of the species of a wide range of plants, herbivores, and carnivores are similar in form, i.e., right skewed when size is plotted logarithmically. In addition to differential extinction and speciation rates, it is argued that allometric con- straints determine the efficiency with which resources are converted into offspring, which in turn determines the frequency of species of different body sizes. In looking for a general explanation for the size distribution shown by all organisms, theorists currently tend to favor explanations based on physiological rather than ecological constraints. Of the body size distributions of predatory ladybird beetles in the Palearctic, Nearctic, Ethiopian, and Australian regions, only that for the Nearctic is significantly right skewed. Even within the Palearctic, the form of the distribution differs among countries, with that for Japan sig- nificantly right skewed and that for Central Europe significantly left skewed. An analysis of the prey of ladybirds indicates that increasing ladybird size is associated with increase in size and/or mobility of their prey. The smallest species feed on mites, and the largest on caterpillars and beetle larvae. In addition, the ratio of the numbers of species of aphi- dophagous to coccidophagous ladybirds in the Nearctic and Palearctic regions reflects the ratio of the numbers of species of aphids to coccids in these two regions. The relationships between egg and adult volumes for 61 species, and egg and adult masses for 26 species both indicate that large species lay larger eggs than small species. In particular, the predators of large and/or active prey lay larger eggs than the predators of small and/or slow moving prey. The relevance of these findings to our understanding of the factors that have shaped body size frequency distributions is discussed. In the case of predatory ladybirds it is concluded that the shape of their body size distribution curves is determined by the nature and the relative abundance of their prey, that is, by ecological rather than physiological constraints.

Assessment of patch quality by ladybirds: relative response to conspecific and heterospecific larval tracks a consequence of habitat similarity?

Summary.Aphid colonies can reach high levels of abundance but last for short periods of time. The larvae of aphidophagous ladybirds (Coleoptera: Coccinellidae) that feed on these colonies might therefore suffer from starvation, which favours the occurrence of cannibalism and intraguild predation. Thus, the assessment of patch quality becomes crucial and it has been shown that female ladybirds refrain from laying eggs in the presence of an oviposition deterring semiochemical deposited by their larvae.Adalia bipunctata (L.), Adalia decempunctata (L.) and Coccinella septempunctata L. are 3 sympatric species of ladybirds, which can co-occur in aphid colonies. As a consequence, their eggs and larvae are under threat, not only from cannibalism but also intraguild predation. Females should, therefore, also use the tracks deposited by heterospecific larvae to assess the quality of aphid colonies as oviposition sites. The expectation is that: 1- the strength of the reaction to each other’s larval tracks should be correlated with percentage habitat overlap and that 2- the reaction to conspecific larval tracks should be stronger than to heterospecific tracks. In order to test these hypotheses, females’ oviposition behaviour was analysed and a chemical analysis of the tracks of their larvae undertaken.The results show that oviposition behaviour is not related to habitat overlap. Both species of Adalia react to tracks of their own larvae and those of C. septempunctata, but A. decempunctata reacted more strongly than A. bipunctata. C. septempunctata reacted very slightly to its own tracks but not to those of either species of Adalia.The larval tracks are mainly composed of alkanes. Those of the two species of Adalia are qualitatively 100% similar and 60% so when the quantitative results are compared. They are, however, only 24–29% similar to those of Coccinella septempunctata.

Towards a mechanistic understanding of temperature and enrichment effects on species interaction strength, omnivory and food‐web structure

Revealing the links between species functional traits, interaction strength and food-web structure is of paramount importance for understanding and predicting the relationships between food-web diversity and stability in a rapidly changing world. However, little is known about the interactive effects of environmental perturbations on individual species, trophic interactions and ecosystem functioning. Here, we combined modelling and laboratory experiments to investigate the effects of warming and enrichment on a terrestrial tritrophic system. We found that the food-web structure is highly variable and switches between exploitative competition and omnivory depending on the effects of temperature and enrichment on foraging behaviour and species interaction strength. Our model contributes to identifying the mechanisms that explain how environmental effects cascade through the food web and influence its topology. We conclude that considering environmental factors and flexible food-web structure is crucial to improve our ability to predict the impacts of global changes on ecosystem diversity and stability.

Chemical protection of Calvia quatuordecimguttata eggs against intraguild predation by the invasive ladybird Harmonia axyridis.

Intraspecific and interspecific predation of eggs is a well documented phenomenon amongst aphidophagous coccinellids. The invasive species Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is known to be a top intraguild predator and reported to attack the eggs of many coccinellid species both in a laboratory setting and in the wild. A previous laboratory study highlighted that while many species’ eggs were highly palatable to H. axyridis, the eggs of Calvia quatuordecimguttata (Linnaeus) (Coleoptera: Coccinellidae) appeared to be extremely well protected from attack. Here we present the results of behavioural experiments testing the hypothesis that substances on the egg surface are responsible for this protection, and report preliminary results of GC-MS analysis of these compounds. When the coatings of C. quatuordecimguttata eggs were removed using hexane, they became significantly more susceptible to predation by neonate H. axyridis larvae. However, their overall palatability was not affected, in that complete consumption was never or rarely observed. This suggests that the surface compounds are a true indicator of unpalatability in this species. The effect of hexane-washing on already palatable conspecific eggs was also analysed but had no significant effect on the susceptibility of eggs to cannibalism. We conclude that the eggs of at least one European species are effectively protected by surface deterrents from intraguild predation by H. axyridis. This effect might be due to both the diversity and abundance of hydrocarbons present within the egg coating, the presence of alkenes and/or the presence of patches of a red substance on the eggs’ surface, which is thought to belong to the acid group. In conjunction with data on the susceptibility of other immature stages of C. quatuordecimguttata, this finding may indicate a decreased risk of the species falling victim to invasive H. axyridis, despite their coincident habitat ranges.

Prey availability in time and space is a driving force in life history evolution of predatory insects.

Environmental constraints can be determinant key factors conditioning predator life history evolution. Prey seems to have conditioned life history evolution in their ladybird predator, with the predators of aphids apparently presenting faster development, greater fecundity and shorter longevity than species preying on coccids. However a rigorous comparison has never been done. We hypothesize that aphids and coccids differ by their developmental rate, abundance, and distribution in the field, which act as ecological constraints promoting life history evolution in ladybird predators. Field data reveal that aphids are ephemeral resources available in the form of large colonies randomly distributed in the habitat whereas coccids form smaller colonies that tend to be aggregated in space and available for longer periods. A comparison in laboratory conditions of two predatory species belonging to the tribe Scymnini (Coleoptera: Coccinellidae) show that the aphidophagous species lives at a faster pace than the coccidophagous: it develops faster, matures earlier, is more fecund, has a shorter reproductive life-span and allocate proportionally more fat in its gonads relative to soma. This indicates that the life histories of aphidophagous and coccidophagous ladybird predators appear to have evolved in response to particular patterns of prey availability in time and space. Under the light of these results, the existence of a slow-fast continuum in ladybirds is briefly addressed.