Measurements of areas consumed from leaf discs by chewing phytophagous insects: Description of a new method involving image processing

Abstract

An automatic method is described which can measure areas consumed from leaf discs by insects. The method is based on digital image processing and is able to compensate for changes in areas which occur during the feeding experiments after the leaf discs have been cut. Calibration with previous methods involving visual counting has been made. The new method proved to be very time-saving and sufficiently accurate for many purposes. The new and the previous method were compared in a study of the relative acceptability of horseradish (Armoracia rusticana G., M. & Sch.), radish (Raphanus sativus L.) and pea (Pisum sativum L.) to two crucifer feeding flea beetle species, Phyllotreta armoraciae (Koch) and P. nemorum L. (Coleoptera: Chrysomelidae: Alticinae). Pea leaf discs were treated with sinigfin, a known feeding stimulant for both species. Choice as well as non-choice tests yielded the same results independant of the method used for estimation of consumed areas. Both species preferred to feed on their host plants in choice tests, P. armoraciae on horseradish and P. nemorum on radish. Relative amounts consumed from non-host plants were higher in non-choice than in choice tests. Inexperienced P. armoraciae consumed similar amounts of horseradish and pea treated with sinigrin in the non-choice tests.

Intraspecific variability in adult flea beetle behaviour and larval performance on an atypical host plant

“…Tests were performed as described by Nielsen (1978) except that smaller vials (V= 158 ml) were used and the same leaf discs were presented to individual beetles for 48 h. After 48 h, the leaf discs were replaced. Consumption of individual leaf discs was measured by a computerized method involving image analysis (Hagerup et al, 1990). The discrimination index D = (B -R)/(B + R) was calculated for the choice tests (B = consumption on B. vulgaris; R = consumption on radish).…”

Intraspecific variability in adult flea beetle behaviour and larval performance on an atypical host plant

“…Tests were performed as described by Nielsen (1978) except that smaller vials (V= 158 ml) were used and the same leaf discs were presented to individual beetles for 48 h. After 48 h, the leaf discs were replaced. Consumption of individual leaf discs was measured by a computerized method involving image analysis (Hagerup et al, 1990). The The available evidence suggests that a single Rgene is sufficient to explain the difference between the 161 YE-and the ST-line.…”

Bioassay Methods with Terrestrial Invertebrates

“…For substrates of even and uniform consistency, such as filter paper disks, membranes, and leaf disks, ingestion is often estimated from the area consumed (but see Waller & Jones 1989). Area can be measured by tracings or photocopying eaten substrates onto graph paper then estimating area consumed, with the use of planimeter ocular grids, electronic area meters, electronic digitizers attached to a computer (e.g., Meade & Hare 1993), or through more sophisticated image processing (Hagerup et al 1990). Implicit in the process of estimating consumption from area are (1) that the test chemical was evenly applied to the substrate and (2) for leaf disks, that there is a constant relationship between dry and fresh weight and that the insects feed completely through the disk.…”