Proportion Of Alatae Research Articles

Colony growth and dispersal in the ant‐tended aphid,Aphis craccivoraKoch, and the non‐ant‐tended aphid,Acyrthosiphon pisumHarris, under the absence of predators and ants

AbstractTo elucidate the potential for colony growth and the dispersal of aphids in relation to the ant attendance, the mobility, tolerance of starvation, colony growth, and dispersal were examined in the ant‐tendedAphis craccivoraKoch and the non‐ant‐tendedAcyrthosiphon pisumHarris under the absence of predators and ants. The increase of the dispersal rate with density was more conspicuous inAc. pisumthanAp. craccivora.The success rate of dispersal was higher inAc. pisumthanAp. craccivora. These results would be derived from the higher ability of dispersal by walking inAc. pisumthanAp. craccivora. The longer legs, higher walking speed, and stronger tolerance of starvation inAc. pisummight result in a higher ability of dispersal by walking. These traits may have developed in relation to non‐ant attendance, becauseAc. pisumaphids frequently escape from natural enemies by dropping from the host plant. On the other hand,Ap. craccivorahave not developed morphological and behavioral traits concerning dispersal by walking, because increasing colony size without dispersal is likely to be advantageous for ant attraction. Escaping behaviors ofAp. craccivorafrom natural enemies have not been well developed due to the ant's defense against natural enemies. The proportion of alatae inAp. craccivorawas higher than inAc. pisuminstead of a lesser ability for dispersal by walking inAp. craccivora. The differences in ant attendance have been influenced in the development of morphological and behavioral traits concerning the dispersal ability, and then, different potentials for reproduction and dispersal have developed in ant‐tended aphids and non‐ant‐tended aphids.

Factors affecting the proportion of soldiers in eusocial bamboo aphid,Pseudoregma bambucicola, colonies

The proportion (percentage to all individuals) of soldier-type first-instar larvae in colonies of the eusocial aphid, Pseudoregma bambucicola, was measured at bamboo stands in Kagoshima Prefecture, Japan, in relation to colony size, percentages of adults and alatae, host conditions and syrphid natural enemies. A significantly positive correlation was found between the soldier proportion and colony size in all 3 months. Multiple regression analysis showed that the colony size and the proportion of alatae had highly significant partial regressions to the soldier proportion. Length of bamboo shoots on which colonies were observed showed a positive correlation to the soldier proportion, but this correlation was not supported by multiple regression analysis. The number of syrphid larvae living in colonies showed a negative, but insignificant, correlation to the proportion of soldiers.

An Experimental Investigation of Inter-Relationships Between the Wood-Ant (Formica rufa) and Some Tree-Canopy Herbivores

SUMMARY (1) Previous work on interactions between F. rufa and some canopy herbivores is briefly reviewed. (2) In limestone woodland in N. England, populations of defoliators (illustrated by the Winter Moth, Operophtera brumata L.), a non-tended aphid species (Drepanosiphum platanoidis Schr.) and a tended aphid species (Periphyllus testudinaceus Fernie), are all affected by the presence of the ant. (3) Predation of D. platanoidis by F. rufa results in significant depression of the population compared with experimental conditions where ants were excluded from shoots. (4) Trees without ants have significantly higher populations of Lepidoptera larvae than do foraged trees. (5) On trees with ants an average of 1% of the leaf area had been removed by defoliators at the end of the season; without ants the total was nearly 8%. (6) Formica rufa tended eight aphid species and one psyllid in the woodland. The association of F. rufa with one of the aphids (P. testudinaceus) was studied. (7) Periphyllus testudinaceus populations were significantly increased in the presence of ants. When ants were excluded from colonies on shoots a significant fall in numbers occurred. There was probably also a reduction in the proportion of alatae. (8) The results are discussed in relation to previous work on aphid predation by ants and to the practice of introducing ants into woodland to protect trees from the effects of defoliators. It is concluded that this practice may be ill-founded.

The role of crowding in the production of winged forms by two strains of the pea aphid, Acyrthosiphon pisum

Apterous females of both strains of Acyrthosiphon pisum responded to being crowded by including some alate daughters in their progenies. Females of the pink strain produced many more alate offspring in response to this stimulus than did the green forms. The proportion of alatae in the progenies of crowded females of both strains was dependent upon both the duration of the treatment and the density of the aphids when crowded. Whereas two individuals of the pink strain when confined together for 24 hr induced a strong response in each other, aphids of the green strain produced few alatae unless confined in groups of 10. Control aphids starved for 24 hr in isolation gave no response. However, winged forms occasionally appeared, apparently randomly, in the offspring of unstarved but isolated pink females. Similar females of the green strain produced only apterous daughters. Larvae of both strains are irrevocably determined as alatae or apterae before their birth. No post-natal response to tactile stimulation or any other environmental factor could be demonstrated. Determination probably takes place shortly prior to birth. The maternal response of the green forms can be triggered by crowding adult females. This treatment, when applied to aphids of this strain prior to the larval-adult ecdyses, does not induce the production of alatae. However, fourth instar, and even third instar, apterae of the pink strain respond to a crowding stimulus by ultimately producing numerous alate daughters. The response to crowding can be ascribed to tactile stimulation only. Removal of antennae diminished the response to crowding considerably. Slow-motion film sequences have shown individuals of the pink strain to be particularly sensitive to encounters with other aphids. A 24-hr period of contact with the rough walls of a confining muslin bag induced in isolated pink aphids a response as intense as that of aphids subjected to any crowding treatment. Females of the green strain did not respond to this stimulus, and cine films show them to be much less sensitive to contact with other aphids than the pink forms.

The distribution of Myzus persicae (Sulz.) on year‐round chrysanthemums

SUMMARYFour cultivars of chrysanthemum (B.G.A. Tuneful, Giant No. 4 White Indianapolis, Bluechip and Yellow Princess Anne) were infested with Myzus persicae (Sulz.) in an insect‐proof glasshouse. Four weeks of rapid reproduction led to temporary overpopulation, but the mean density was soon regulated to a constant level by the production of alatae. When the density was highest, the same proportion of alatae was produced in all regions of the plants and on all cultivars, regardless of population density at the site of eclosion. This was thought to be due to the rapid state of flux in the entire population.Pronounced varietal differences developed in the size and distribution of populations, Tuneful supporting six times as many aphids as Princess Anne. Vertical distribution of aphids on the plants differed not only with cultivar, but also according to the population density and the developmental stage of the plant. A complete redistribution occurred as the density stabilized, revealing further varietal characteristics. The youngest leaves were always the most attractive to the aphids, and preference was frequently shown for their upper surface, particularly on Princess Anne.Short days had little direct effect on the behaviour of the aphids. The induced flowering, however, brought inevitable changes in aphid distribution; populations tended to move upwards towards the flowers, resulting in small, damaged and infested blooms.