The pea aphid, Acyrthosiphon pisum (Hemiptera: Aphididae), is a well-studied species in terms of its colour polymorphism, where it occurs as two distinct colour morphs, red and green. It is proposed that the occurrence and maintenance of this polymorphism is an adaptive response to environmental factors, in particular natural enemies and host plant quality. We hypothesized that these adaptations are directly mirrored in the energy reserves accumulated by the different colour morphs during their pre-adult stages and reflect their specialization for particular ecological roles. We quantitatively measured the different energy reserves of red and green pea aphids and found that the total energy reserves of these morphs did not differ. Interestingly, these reserves were made up of different components in the red and green colour morphs. There was a higher percentage content of water-soluble carbohydrates and lipids in the red clones and higher percentage content of protein in green clones. These finding are in accordance with green clones being more fecund than red ones and needing more protein for reproduction than red clones, which produce more winged offspring when crowded or in response to the presence of natural enemies and so, need more lipids and carbohydrates to fuel their walking and flight. Apparently, different colour morphs are physiologically specialized to adjust their energy reserves in relation to their specific ecological adaptations and maximize their fitness in terms of dispersal, reproduction, defense and survival., Seyed Mohammad Ahsaei ... []., and Obsahuje seznam literatury
Monoctonus paulensis is a solitary parasitoid of several species of aphids, including the pea aphid, Acyrthosiphon pisum. We evaluated host-instar selection by comparing the parasitoid's preference for the four nymphal instars of the pea aphid, presented two at a time in dichotomous choice tests. Females parasitized more, and laid more eggs in, the relatively smaller aphids among those available. This preference was independent of aphid instar: L1 > L2 > L3 > L4. Preference was not influenced by female size or age. Normal and anaesthetized aphids were accepted equally. The total time needed by a female to capture, position, and parasitize an aphid varied among host instars, with fourth instars requiring nearly twice as much time as first, second, and third instars. The probability of an attacked aphid escaping or avoiding parasitism increased with aphid instar, from ~10% in first and second instars to ~50% in fourth instars. Although fourth-instar pea aphids contain more resources for offspring development than smaller counterparts, it may not be profitable for a female to invest opportunity time in attacks on large aphids.
Interclonal variability in the photoperiodic responses of the pea aphid Acyrthosiphon pisum and intraclonal differences between wingless viviparous females (=apterae) and winged viviparous females (=alatae) were studied. In 7 clones collected from peas near St.Petersburg the effect of constant diel photoperiods (from 0L : 24D to 24L : 0D at 20°C) on sexual morph determination and dynamics of morph production were recorded. Apterae of 5 clones and apterae and alatae of 2 clones were studied. The mean and age-dependent fecundity of apterae and alatae were compared. The clones studied in detail can be divided in two groups. The first includes clones that produced winged males and had critical photoperiods for female morph determination around 12L : 12D. The second includes clones with critical photoperiods for female morph determination around 17L : 7D; these clones produced wingless males, and one clone produced only oviparae. The intraclonal differences in the photoperiodic limits for ovipara and male production depended on the clone-specific abundance of males. The shapes of the photoperiodic curves for male production also depended on the clone-specific abundance of males. In short-day conditions alatae produced more oviparae and fewer males, and the range of photoperiods that induced ovipara production in alatae was nearly twice as wide as that in apterae. The photoperiodic limits for ovipara and male production differed for apterae and alatae. The fecundity of alatae was lower, although they reproduced for longer and lived longer than apterae. Both apterae and alatae reproduced more intensively over the first 2 weeks. Apterae and alatae began to produce males at the same age. Because of their late onset of larviposition, the reproductive pause that divides female and male production was obscured in alatae. Both apterae and alatae tended to produce initially and finally batches of viviparous offspring, possibly reflecting age-dependent endogenous changes in the hormonal titres in the parents.
Macrolophus pygmaeus (Hemiptera: Miridae) is an important predator of pests of horticultural crops and here its ability as a predator of Acyrthosiphon pisum (Hemiptera: Aphididae) is addressed for the first time. The percentage predation of the different aphid instars and the number partially consumed were studied. Our results, obtained using choice and no-choice tests, revealed that M. pygmaeus caught and consumed more young than later instars of A. pisum, which confirms results of previous studies using other species of aphids. We also studied the interactions between predators (male/female) foraging in the same patch. When the prey/predator ratio is kept constant at 10 : 1 the average percentage of aphids completely consumed by individual females or males does not change with increase in the number of foraging predators. However, the number of partially consumed aphids decreased when females shared the same patch. In contrast, there was an increase in the number of aphids partially consumed when two males shared the same patch. The results were discussed in terms of potential predator foraging strategies since intraspecific competition is a key factor modulating the dynamics of prey-predator systems., Juliana Durán Prieto, Vincenzo Trotta, Paolo Fanti, Cristina Castañé, Donatella Battaglia., and Obsahuje bibliografii