A Method for estimating Populations and counting large Numbers of Aphis fabae Scop

Abstract

It is often necessary to estimate the numbers of Aphids in the field over a period of time, a problem which is accentuated when the species concerned is very numerous. This paper describes a method for estimating population changes of the Black Bean Aphid, Aphis fabae Scop., on beans, and a simple volumetric method for counting large numbers of the Aphid in the laboratory. The method, which might be applied for other small arthropods, is illustrated by the results obtained from a study of three bean plots during the summer of 1952.The essentials of the method are as follows: in the field, a large number of bean stems was examined and each placed in one of five arbitrary classes of Aphid nfestation. Sample stems of each of these classes were removed from the plot bo the laboratory and the Aphids on each stem counted. The mean numbers of Aphids for each of the classes, estimated from the sample results, were multiplied by the appropriate number of stems of each class and the products, when added, gave an estimate of the Aphid population of all the stems examined in the field.The adoption of a system of classification of stems in the field not only allows a large number of stems to be examined but also eliminates the necessity of removing a large number of samples. Similar systems were used by Gorham in surveys of potato Aphids (see Broadbent, 1948) and by Ripper (1944) for Aphids on brussels sprouts. The present classification is developed from a method used by C. G. Johnson and J. A. Nelder (unpublished work) for Aphid populations of beans.

A method for estimating populations ofAphis craccivoraKoch on cowpea

“…However, the categorization made by Banks (1954) was based on quick impressions of infested stems and did not consider their length and thickness. Similarly, Kumar (1971) categorized infested stems and pods of mustard into three classes and estimated the aphid number per unit length of stem or pod but did not take into account their thickness.…”

“…Most of the workers who attempted to devise methods for estimating aphid populations in situ used infestation scales and placed plant parts in different classes of infestation (Banks, 1954;Swirski, 1954;Way and Heathcote, 1966;Kumar, 1971). In all these cases, the average number of aphids on plant parts was calculated in each class in the laboratory and these averages were used for estimating populations in the field.…”

The development of an electronic aphid-counter

“…The system of aliquot sampling as used by Banks ( 1954) In counting the bean aphid was also examined and tested.…”

“…It was hoped to develop a system of sampling and counting which would not err by more than -+-5%. The error of systems examined varied from that given by Banks (1954) with a maximum of ± 24% for certain classes of samples to that outlined by Strickland (1957) in which fcur classes of rankings were used. When translated to "rounded off weighting values", with twelve observers available and peak densities averaging 1,531 aphids per plant over three years, and after statistical manipulation, errors varied from 7.7% to 1.1% for different ranks.…”

Bean Aphid Control on Field Beans in Relation to the Flowering Period and to Honey Bee Poisoning

“…In 1954-55 a tractor-mounted field sprayer was used to apply 22 oz demeton in 140 gal of water per acre in 1954, and 6 oz demeton-methyl in 60 gal of water per acre in 1955. Other details are given in Table 1.The numbers of bean aphids were estimated at about weekly intervals bj categorising the aphid populations on 40 (year 1953) or 400 (years 1954-5) stems at random in each treatment (Banks, 1954). The mean number of aphids in a category was obtained by removing and counting the aphids on at least seven infested stems in that category.…”