Differentiating between black field cricket and black beetle damage in Northland pastures under drought conditions

Abstract

Widespread and severe pasture damage occurred on many farms in northern regions of Northland during the 1982-83 drought. Eight farms were investigated where black beetle, Heteronychus arator (Fabricius) (Coleoptera : Scarabaeidae), was assumed to be responsible for the damage. Black beetle adults, eggs of black field cricket, TeleogrylIus commodus (Walker) (Orthoptera: Gryllidae), and other insect pests were extracted by hand sorting and wet sieving soil cores taken from damaged pasture. The presence of black beetle larvae and crickets was also determined from an examination offrass and by noting the presence of tunnelling or soil fractures. Black beetle and crickets were the only insect pests found in abundance. Black beetle numbers were moderate (35/m2) or high (l09/m2) on the 2 farms with sandy soils (yellow-brown sands) but were low ( < 14/m2) on the 6 farms with clay (northern yellow-brown earths) or semi-volcanic soils (brown and granular loams and clays). Black field cricket egg densities were > 1000/m 2 and the frass recovered was predominantly from crickets on the 6 farms with clay and semi-volcanic soils. This suggested that cricket populations had been > 40-1 00/m2 and that crickets were responsible for the severe pasture damage that occurred on the 6 farms with clay and semi-volcanic soils, whereas black beetles were associated with the severe pasture damage that occurred on the 2 farms with sandy soils.

Effect of black beetle, in association with nitrogen and summer spelling, on pasture production on sandy soils

“…In contrast, densities on ryegrass-based pasture were maintained at lower levels. A similar preference for kikuyu grass was found on a Redhill sand near Dargaville where average lO-year summer larval densities on kikuyu grass pasture were 40/m 2 (SE ± 8) compared to ryegrass pasture of 19/m2 (SE ± 4) (Blank 1986). …”

“…Severe pasture damage occurred close to these trial sites in 1982/83 when rainfall was 70% less than normal (Blank et al 1986). However, the black beetle densities of35/m 2 and 112/m 2 recovered from ryegrass and kikuyu grass pasture, respecti vel y, were similar to those encountered in this study.…”

“…The 500-560 kg dry matter (DM)/ha loss in pasture production over the summer and autumn periods in the black beetle-infested plots was not significantly different from that in insecticide-treated plots. The effect of naturally occurring black beetle populations on pasture production was assessed from 1976 until 1985 on a Redhill sand near Dargaville (Blank 1986). Black beetle summer larval populations ranged up to 40/m 2 in ryegrass-dominant and 77 /m2 in kikuyu grass-dominant pastures without markedly influencing pasture production or causing damage.…”

“…In the 1970s, black beetle was considered to have spread onto the heavy clay soils and to have caused considerable pasture damage throughout the Auckland and Waikato regions (White 1972;Reynolds & Langton 1973;Laurenson 1974). Blank et al (1986) investigated eight farms in Northland where black beetle was blamed for causing severe pasture damage following the 1982/83 drought. Black field crickets, Teleogryllus commodus (Walker), were responsible for the damage on six farms with clay and semi-volcanic soils, whereas black beetles were associated with the damage on the two farms on sandy soils.…”

“…Black field crickets, Teleogryllus commodus (Walker), were responsible for the damage on six farms with clay and semi-volcanic soils, whereas black beetles were associated with the damage on the two farms on sandy soils. Soils susceptible to black beetle attack were thus considered to be limited mainly to the coastal sands and peaty soils which occupy about 12% of Northland (Blank 1985).…”