Aphid Life Cycle and Distribution
– Aphids undergo a typical life cycle with flightless females giving live birth to female nymphs.
– Female nymphs can also be already pregnant, known as telescoping generations.
– Females breed profusely, resulting in rapid multiplication of aphids.
– Winged females develop later in the season, allowing colonization of new plants.
– Sexual reproduction occurs in the autumn, with overwintering as eggs.
– Aphids are distributed worldwide, but most common in temperate zones.
– They can migrate great distances through passive dispersal by winds.
– Winged aphids can rise up to 600m and be transported by strong winds.
– Some species have spread through easterly winds and human transportation of infested plant materials.
– Certain species have become nearly cosmopolitan in their distribution.
Aphid Evolution and Fossil History
– Aphids, adelgids, and phylloxerans evolved from a common ancestor around 280 million years ago.
– The oldest known fossil of an aphid species is from the Triassic period.
– Amber has preserved around sixty aphid species from various periods.
– The diversification of flowering plants led to the speciation and specialization of aphids.
– Ancestral aphids may have lived on conifers or angiosperm bark before switching to leaves.
– Aphids do not fossilize well due to their soft bodies.
– The appearance of angiosperms led to an increase in aphid species.
– The Phylloxeridae family is the oldest extant family, with limited fossil records.
Aphid Taxonomy and Anatomy
– Aphids are classified within the suborder Sternorrhyncha, along with adelgids and phylloxerids.
– The infraorder Aphidomorpha includes the superfamily Aphidoidea, Phylloxeroidea, and Adelgoidea.
– Some classifications include a single superfamily Aphidoidea, while others have Aphidoidea and Phylloxeroidea as sister superfamilies.
– Recent reclassifications have rearranged families and elevated subfamilies to family rank.
– The Aphidoidea superfamily includes the Aphididae family with approximately 5000 extant species.
– Aphids have soft bodies in various colors.
– They have antennae with two short and broad basal segments.
– Aphids possess a pair of compound eyes with ocular tubercles.
– They feed on sap using stylets and a sheath called a rostrum.
– Aphids have long, thin legs with two-jointed, two-clawed tarsi.
Aphid Reproduction and Factors Affecting Reproduction
– Aphids can have sexual (holocyclic) or asexual (anholocyclic) generations.
– Some species can have both types of populations under different circumstances.
– No known aphid species reproduce solely by sexual means.
– The alternation of sexual and asexual generations may have evolved repeatedly.
– Aphid reproduction can involve migration between different host plants.
– Winged progeny tend to be produced more abundantly under unfavorable or stressful conditions.
– Winged females migrate to start new colonies on a new host plant.
– Predators and viral infections can change the dynamics of aphid reproduction.
– Alarm pheromones released by aphids when attacked can induce the production of winged progeny.
– Symbiotic bacteria inside aphids can alter aphid reproductive strategies based on environmental stressors.
Aphid Interactions with Ants and Bacterial Endosymbiosis
– Ants, such as Lasius flavus, manage large herds of aphids that feed on plant roots in their colonies.
– Queens take aphid eggs to start new herds in new colonies, protecting them from predators.
– Some bees collect aphid honeydew to make forest honey.
– Lycaenid butterflies lay eggs on plants tended by ants, and the caterpillars feed on the aphids.
– The caterpillars produce a pheromone that deceives ants into treating them as ants and carrying them into their nests.
– Paracletus cimiciformis is an aphid that mimics ants and uses a double strategy involving two morphs.
– Aphids have a symbiotic relationship with Buchnera aphidicola, a bacterium transmitted vertically from parent to offspring.
– Five genes from the bacteria have been transferred to the aphid nucleus.
– The association between aphids and Buchnera is estimated to have occurred 280 to 160 million years ago.
– Buchnera provides aphids with essential amino acids found in low concentrations in plant sap.
– Metabolites from endosymbionts are excreted in aphid honeydew.
– The stable intracellular conditions and bottleneck effect during transmission increase the probability of mutations and gene deletions.
– The size of Buchnera aphidicola genome is greatly reduced compared to its ancestor.
– Despite the reduced genome, gene expression is highly regulated in Buchnera.
– There is a ten-fold variation in gene expression levels under normal conditions.
– Aphids feed on the phloem-sap of vascular plants.
– The symbiotic relationship with Buchnera allows aphids to exploit this ecological niche.
– Buchnera provides essential amino acids that are scarce in plant sap.
– Aphids transmit mutations and gene deletions during the transmission from mother to nymph.
– Aphids play a role in the transmission of endosymbiont metabolites through their excretion in honeydew.
