Population phenology of whitefringed weevil, <i>Graphognathus leucoloma</i> (Coleoptera: Curculionidae), in pasture in a Mediterranean-climate region of Australia

Growth of larvae of the whitefringed weevil, Graphognathus leucoloma (Boheman), was studied in the laboratory and on various crops in pots in a shadehouse at Kairi, on the Atherton Tableland in north Queensland. In the laboratory at 25.5 ± 1°C there were 11 instars for which head capsule widths and weights were recorded. The first instar weighed 0.14 mg. This was a nonfeeding stage capable of prolonged survival, and after 10 weeks in soil without food 60% survived. When provided with carrot (Daucus carota) larvae grew to 2 or 3 mg after 6 to 7 weeks, then increased rapidly in weight reaching 140 mg after 120 days. At 25.5°C the average time from first instar to adult was 311 days, due in part to a long prepupal period. Larval growth was measured on the roots of peanut (Arachis hypogaea) plants in pots in summer and winter. Under summer conditions (mean soil temperature 23.3°C) larvae reached 140 mg in about 120 days, similar to that in the laboratory on carrot. These fully grown larvae remained in the pots over the mild winter without pupating. Larvae developing in autumn/winter grew more slowly, but the fully grown larvae were then exposed to high spring (early summer) temperatures and soon pupated, the average time from first instar to adult being 273 days. The indications are that temperatures above 25°C quickly precondition mature larvae from Tolga for pupation, thus explaining the broad timing of adult emergence in the field in north Queensland. On different plants common near Tolga, larvae grew most quickly on peanuts and on the pasture legumes dolichos (Lablab purpureus) and stylosanthes (Stylosanthes guianensis). Survival on maize equalled that on peanuts (46.5% in sterilized soil) but growth was less. Larval survival and growth on the grass crowsfoot (Eleusine indica), and (surprisingly) on the pasture legume glycine (Neonotonia wightii) was very poor.

Section: Significance Of the Non-feeding First Instarmentioning

confidence: 99%

Section: Growth and Development Of Larvaementioning

confidence: 99%

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Development of larvae of the whitefringed weevil,Graphognathus leucoloma(Coleoptera: Curculionidae), in northern Queensland

Gough

Brown

1991

“…The infrequent occurrence of insects at the site of damage further indicates their propensity to move about. The frequency and intensity of tuber damage thus tended to increase during the growth of the crop, exacerbated in spring crops by the growth of G. leucoloma larvae coinciding with that of the crop (Matthiessen, 1991;Matthiessen & Learmonth, 1992). This gave the appearance of increasing larval density as more larvae became visible, while in summer crops tuber damage could be heightened by immigration of H. arator adults.…”

Section: Discussionmentioning

confidence: 99%

Impact of the soil insects African black beetle, Heteronychus arator (Coleoptera: Scarabaeidae) and Whitefringed weevil, Graphognathus leucoloma (Coleoptera: Curculionidae), on potatoes and effects of soil insecticide treatments in south-western Australia

Matthiessen

Learmonth²

1995

Populations of the soil insects African black beetle, Heteronychus arator (Fabricius), and whitefringed weevil, Graphognathus leucoloma (Boheman), and the damage caused to potato crops in south-western Australia were measured with and without the insecticide chlorpyrifos incorporated into the soil prior to planting. Low populations of both insects were highly damaging. Destruction of stems by H. arator reduced tuber yield and both species damaged tubers from the time of their formation. Tuber damage increased with time because both insect species on average damaged multiple tubers and caused multiple attacks on tubers. Growth of G. leucoloma larvae caused increased abundance of the more damaging later instars in spring. The insecticide reduced resident H. arator abundance and hence damage to newly-emerging potato stems in summer, but had less effect on reducing attacks on tubers in summer crops because adult beetles flew into some crops during growth. Exceptionally high tuber damage per H. arator adult in winter crops was ascribed to enhanced activity during its spring breeding season. The insecticide was inconsistent in reducing the abundance of G. leucoloma larvae. Insecticidal effects were greatest near the soil surface, resulting in an increase in the relative proportion of both insects deeper in the soil. Since a greater proportion of the tubers occurred there, the resulting greater potential for the insects to cause tuber damage tended to outweigh reduction in their abundance.

“…Efforts to improve consistency of chemical control or develop integrated approaches to management have been restricted by a paucity of information on the ecology of the insects in the south-western Australian potato-growing regions. Studies of the general biology and phenology of H. arator in the principal pasture habitat have recently been reported by Matthiessen & Ridsdill-Smith (1991), and of G. leu-coloma by Matthiessen (1991) and Matthiessen & Learmonth (1992). A complementary requirement was to better understand the ways in which the insects cause economic losses to potatoes.…”

Section: Introductionmentioning

confidence: 99%

Spatial sampling of insects, plant parts and insect attacks in the soil of potato crops

Matthiessen

Learmonth²

1993

A method was devised for spatial sampling within the soil in potato crops where the soil insects African black beetle, Heteronychus arator (Fabricius) (Coleoptera: Scarabaeidae) and whitefringed weevil, Graphognathns leucoloma (Boheman) (Coleoptera: Curculionidae) are pests. The number and position of potato plant parts, the soil insects, and their attacks on potatoes were defined within the hilled-up soil profile of sections of the planting rows. Neither potato tubers, nor insects nor insect attacks were uniformly distributed. Tubers occurred mainly in the middle of the hill, while the insects contrasted in their distribution in the soil. Most of the damaging H. arator adults and larvae occurred in upper middle areas; the damaging G. leucoloma larvae occurred deeper and were more damaging on the under-side of tubers. The method provides a means of simultaneously sampling soil insect populations in a crop and obtaining a direct assessment of their damage and the effectiveness of control measures.