Larvae of sugarcane soldiei-fly, liiopirs rrrbriceps, began aggregating near sugarcane plants in trough5 within 1 week of planting. By 6 weeks. almost 80% of larvae were found within 13 cm of the plants and only 5mo \veIe found 25-50 crn distant.Sugarcane soldier fly. Inopus rubriceps (Macquart), is a pest of sugarcane in Australia (Hitchcock 1970). The soil-dwelling larvae feed on sugarcane roots, causing poor growth and failure of ratooning aftzr harvest. Damage is usually seen in crops that are older than second ratoon (Samson et ul. 1991). However, larvae are often present in low numbers in newly-planted crops that follow ploughout of infested sugarcane (unpublished data).A number of insecticides were effective against larvae of I . rvbriceps in bioassays (Samson 1992). One strategy of insecticide use is to apply insecticides in the plant crop, to reduce numbers of larvae carried over from the previous cropping cycle. This may delay build up of larvae in subsequent ratoon crops by reducing the initial breeding population. This strategy is presently being tested.Larvae of I. rvbriceps are aggregated along rows of established sugarcane (Robertson 1984;Samson and McLennan 1992) so insecticides should be applied most efficiently along the rows. However, larvae are presumably dispersed throughout fields when cane is first planted after fallowing and soil cultivation. We did not know how long it would take larvae to concentrate on the newly-plantedrows. An estimate of this time is necessary to determine the best time of insecticide application. Application soon after planting is desirable, as the planting drill is then fully open and plants will not have begun stooling out. However, insecticide applied too early may be lost before larvae are attracted to the rows.Densities of larvae in newly planted sugarcane fields are too low to measure larval attraction to rows. Therefore, we obtained the necessary information using larvae and sugarcane plants in troughs. The troughs measured 1 r n long x 20 cm wide x 15 cm deep, the length being chosen to approximate the commercial sugarcane row width of 1.4-1.5 m. Larvae were collected from sugarcane fields in November. Eighteen troughs were filled with red volcanic soil (krasnozem) and 60 larvae were added evenly along the length of each trough. Four cuttings (setts) of cane stalk, each containing a single bud, were planted beside the midline of each trough 1 week later. Soil was subsequently removed from the trough in eight segments of equal size (Fig. 1). Pairs of segments 1 50 38 25 13 o 1 3 25 38 50Distance from midline (cm) Fig. 1. Sampling desigi of troughs used to measure aggregation of larvae of lt7opus rubriceps. Soil was sampled in eight segments and the segments combiiied as indicated by similar shading; the central black box represents the position of the sugarcane setts.equidistant from the midline were combined and larvae extracted by wet-sieving. Three troughs were sampled at each of six times up to 6 weeks after planting. The first sampling at 0 weeks was carr...
The distribution of cysts of Eumurgarodes luingi in soil and the seasonal phenology of the difi-rent life stages were examined in sugarcane fields near Bundaberg. Cysts were widely distributed i n soil, occurring in equal numbers in both the planting rows of sugarcane and most or all of the inter-row space. Cysts were smaller at increasing distance from the sugarcane plants. Most cysts were found in the top 20 cm of soil but some occurred to a depth of at least 50 cm. Cysts of Ploniur~[/roi/..s spp. were also found in one field. These had a similar lateral distribution to E. luingi but a greater proportion occurred more than 20cm deep. Adults of E. laingi were found from October to February in the four fields examined in 1993 and 1994. Adults were found in the greatest numbers in November. but they comprised less than 10%0 of the total E. laingi population at any time. A large number of cysts of all sizes was present throughout the year, and the results indicate that most individuals had a life cycle of at least 2 years. The large reservoir of cysts during the adult emergence period explains why E. luirigi has proved difficult to control with insecticides and with cultural methods during this supposedly vulnerable time.Eumurgarodes Iuingi, pink ground pearl, Promurgaroci'os spp., seasonal phenology, sugarcant:.
The distribution of cysts of Eumargarodes laingi in soil and the seasonal phenology of the dierent life stages were examined in sugarcane ®elds near Bundaberg. Cysts were widely distributed in soil, occurring in equal numbers in both the planting rows of sugarcane and most or all of the inter-row space. Cysts were smaller at increasing distance from the sugarcane plants. Most cysts were found in the top 20 cm of soil but some occurred to a depth of at least 50 cm. Cysts of Promargarodes spp. were also found in one ®eld. These had a similar lateral distribution to E. laingi but a greater proportion occurred more than 20 cm deep. Adults of E. laingi were found from October to February in the four ®elds examined in 1993 and 1994. Adults were found in the greatest numbers in November, but they comprised less than 10% of the total E. laingi population at any time. A large number of cysts of all sizes was present throughout the year, and the results indicate that most individuals had a life cycle of at least 2 years. The large reservoir of cysts during the adult emergence period explains why E. laingi has proved dicult to control with insecticides and with cultural methods during this supposedly vulnerable time.
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