Gd. Inglis et al., EFFECT OF BAIT SUBSTRATE AND FORMULATION ON INFECTION OF GRASSHOPPER NYMPHS BY BEAUVERIA-BASSIANA, Biocontrol science and technology, 6(1), 1996, pp. 35-50
The effects of two formulations (oil and water) and two bait substrate
s (lettuce and bran) on infection of grasshopper nymphs (Melanoplus sa
nguinipes) by Beauveria bassiana were investigated. More nymphs died o
f mycosis after they had ingested substrates inoculated with conidia i
n oil than in water, but there was no difference between the lettuce a
nd bran substrates. Of the conidia recovered in frass, most (95%) were
recovered within 24 h of ingestion of the lettuce and bran substrates
by nymphs. Significantly more conidia averaged over time were recover
ed in frass from the water than from the oil formulation. A higher inc
idence (33-82%) and more rapid onset of mycosis was observed in nymphs
that were surface sterilized before ingestion, compared with those su
rface-sterilized after ingestion of lettuce and bran substrates inocul
ated with B. bassiana in both formulations. A similar trend was observ
ed in nymphs receiving the sterilization treatment before, rather than
after, ingestion of wheat leaves sprayed with conidia in oil or water
. Numerous conidia were observed on the heads, thoraxes and abdomens o
f nymphs that ingested treated lettuce or bran. Modest numbers of coni
dia were also recovered from the surfaces of nymphs, but not differenc
es were observed between formulations or substrates. However, when nym
phs ingested lettuce disks treated with fluorescent dye in either oil
or water, more dye was observed on nymphs with the oil formulation. Th
is laboratory study demonstrates that grasshopper nymphs are highly su
sceptible to infection by conidia formulated on bait substrates, and t
hat the efficacy of the bait relies on the extent to which nymphs beco
me surface-contaminated during ingestion.