Phratora laticollis
Phratora laticollis is a species of leaf beetle found in Europe and Asia. This beetle is found on Populus species and the chemistry and production of its larval defensive secretions and host plant relationships have been studied extensively. Description. This small (3.7-5mm) beetle is similar and size and coloration to other species of "Phratora". Adults are typically metallic blue or green. In Europe, it is most likely to co-occur on Populus host species with two other "Phratora" species "Phratora vitellinae" and "Phratora atrovirens". It is larger and more abundant than "P. atrovirens" and somewhat narrower  in body shape than "P. vitellinae". Eggs are typically laid in clutches of 8-16, arranged in rows on the underside of the host leaf. Like other "Phratora" species, eggs are partially covered with a crusty secretion. Larvae feed in groups in early instars (molts), and sometimes show color polymorphisms. Range. "Phratora laticollis" has a widespread distribution. In Europe, it is found in Arctic regions and the Nordic countries, the United Kingdom, Germany to Spain, Serbia and Bosnia, and Bulgaria. It is also found in China and elsewhere in Asia. Populations occur at high elevations in parts of central Europe  and China. Habitat and host plants. "Phratora laticollis" adults feed and lay eggs on Populus trees, including "Populus tremula", "Populus nigra", and "Populus alba". Their larvae develop on the same host plants as adults. Their host plants belong to the family Salicaceae, but unlike the willow species (Salix) that other Phratora species favor, Populus species all contain relatively high levels of salicylates in their leaves. Laboratory feeding tests showed that the phenol glycosides (salicylates) characteristic of Populus species stimulate "P. laticollis" feeding. They are also attracted to volatile compounds emitted by host trees, which may explain preferences based on host  plant gender and prior history of insect herbivory. Life history. Lühmann (1939) described the life history of a population in Germany in detail. After overwintering, adult beetles seek mid-sized trees of "Populus tremula" within aspen groves for feeding, oviposition, and production of the summer generation. When spring arrives, overwintered beetles spend 2-3 weeks feeding and lay up to 250 eggs on the undersides of leaves. After eggs hatched, larvae spent about 5-6 days in the first, second, and third instars before leaving the host plant and making a pupal case. After about six days, adults emerge and  remain in the pupal case for an additional two days before emerging. In central Europe, this species can experience multiple generations per growing season (multivoltine), but it appears to undergo only one generation per summer in the Nordic countries or at high elevations. Overwintering was observed under the bark of fir trees near the Populus tremula stand where beetle populations had been found. Van der Laak (1982) investigated the mechanisms of cold tolerance and overwintering success in "P. laticollis." These studies revealed that "P. laticollis" can be 'freeze-tolerant' in summer and winter. Multiple mechanisms influence cold tolerance and it  varies over the year partly due to the concentration of metabolic products such as glycerol and other factors. Larval secretion chemistry. "Phratora laticollis" larvae secrete a defensive secretion that contains iridoid monoterpenes that they synthesize themselves (autogeneously), while their congener "Phratora vitellinae" sequesters host plant salicylates to make its larval defensive secretion. Using host plant compounds to make the larval defensive secretions appears to be the evolutionarily advanced or derived state of this trait, but "P. laticollis" appears to be pre-adapted to evolve the use of host plant salicylates to produce its defensive secretion. Larvae of "P. laticollis" already  possess systems to transport plant secondary compounds that can be modified to sequester those compounds for their own defense. Natural enemies. Lühmann (1939) described a fly predator that consumed the eggs and larvae of "P. laticollis" and these descriptions suggest that it was the syrphid fly "Parasyrphus nigritarsis." He also mentioned the presence of tachinid fly parasitoids that attacked "P. laticollis" larvae but emerged when the beetle reached the adult stage. These parasitoids might be "Medina luctuosa," which others observed attacking "P. laticollis" adults along with a braconid wasp in the genus "Perilitus", which is likely "Perilitus brevicollis," a known  parasitoid of "Phratora vulgatissima". Larvae are also parasitized by "Meigenia mutabilis", a tachinid fly The bug "Rhacognathus punctatus" consumes adult beetles. Most likely, the bug "Anthocorus nemorum" consumes "P. laticollis" larvae. The wasp "Symmorphus bifasciatus" feeds on larvae of "Phratora" species, including "P. laticollis". Overall, many of the same species that feed on "P. laticollis" also consume other "Phratora" species and other leaf beetles, which often occur on the same host plants and similar habitats. Some of these enemies appear to be attracted to leaf beetle secretions. Taxonomy. Species in the genus "Phratora" are morphologically fairly uniform, but vary substantially  in their host plant preferences. Ge (2005) noted that a newly described "Phratora" species in China, "P. quadrithoralis," closely resembles "P. laticollis." Within Europe, the closest relative to "P. laticollis" appears to be another specialist on "Populus," "P. atrovirens."