Akhurst, R.J.

Bedding, R.A.

Bull, R.M.

Smith, D.R.J.

Horizon / Pleins textes

Fundam. appl. Nemacol., 1992,15 (1),71-73.
An epizootic of Heterorhabditis spp.
(Heterorhabditidae : N ematoda)
in sugar cane scarabaeids (Coleoptera)
Raymond]. AKHURST *, Robin A. BEDDING *, Richard M. BULL ** and Donald R.]. SMITH ***
* CSIRO Division of Entomology, C.P.O. Box 1700, Canberra, ACT 2601, Australia;
** Bureau of Sugar Experirnent Statiom, P.o. Box 651, Bunda6erg, Qld 4670, Australia,
and H* Biotech Australia Ply Ltd, P.O. Box 20, Roseville, NSW 2069, Australia.
Accepted for publication 18 February 1991.
Summary - Two Helerorhabdicis spècies were found causing an epizootic among four species of scarabaeid grubs feeding on
sugar cane. The epizootic extended over 5 ha and it was estimated that tens of thousands of grubs were infected at the time of
sampling. Helerorhabdicis were detected in 65 % of soil samples, with 3 % of samples containing both species. Infection rates among
grubs collected from different parts of the fields varied between 26 % and 100 %.
Résumé - Heterorhabditis spp. (Heterorhabditidae : Nematoda) épizootiques envers des scarabéides (Coleoptera) de
la canne à sucre - Deux espèces d' Helerorhabdilis ont été trouvées qui causent une épizootie envers les larves de quatre espèces
de scarabéides se nourrissant sur canne à sucre. Cene épizootie s'étend sur 5 ha et il est estimé qu'au moment de l'échantillonnage
des dizaines de milliers de larves étaient infestées. Helerorhabdilis a été détecté dans 65 % des échantillons dont 3 % contenaient
j'une et l'autre espèces. Le taux d'infestation des larves d'insectes varie, dans les différentes parties du champ, de 26 % à 100 %.
Key-words : Epizootie, Helerorhabdilis, Scarabaeid, sugar cane.
Heterorhabditis spp. are pathogens of a wide range of
pest insects. The infective stage of these nematades is a
soil-dwelling, third instar juvenile that may survive
months without feeding. Infeetive juveniles are attracted
ta insects (Bedding & Akhurst, 1975) and invade via
natural orifices (Poinar, 1979) and through interskeletal
membranes (Bedding & Molyneux, 1982). They pene-
trate ta the haemocoel where they release cells of a
syrnbiotic bacterium, Xenorhabdus luminescens (Tho-
mas & Poinar, 1979) that have been carried within their
intestines. These bacteria multiply, killing the host and
generaring conditions suitable for feeding and reproduc-
tion by the nematodes. Afrer one or !Wo cycles a new
generation of infective juveniles carrying their symbiotic
bacteria emerges from the cadaver ta infect new hosts.
Use of a baiting method for detecting entomopatho-
genic nematades in soil (Bedding & Akhurst, 1975) has
shown that Heterorhabditis spp. are widely distributed
throughout the world (Beavers et al., 1988; Akhurst &
Brooks, 1984; Akhurst & Bedding, 1986; Mràcek &
]enser, 1988). However, there are few reports of natural
infection by Heterorhabditis spp. and there has been only
one report of an epizootic produced by a Heterorhabditis
sp. (Sextan & Williams, 1981).
Although Heterorhabditis spp. are weil distributed in
sugar cane fields in Australia (Akhurst & Bedding, 1986)
and scarabaeids are the major pests of sugar cane in
Australia, there have been no reports of natural infec-
tion of cane scarabaeids by these nematodes. When one
of us (RMB) detected infected scarabaeid grubs in a
young first rataon cane field near Bundaberg, the survey
described in This paper was conducted ta detennine the
extent and significance of the infection.
Materials and methods
The Occurrence and distribution of nematades and
infected grubs was determined by taking 500 cm3 sam-
pies ta 0.2 m depth at approximately 15 m intervals
throughout the three adjoining fields (5 ha) where in-
fected grubs had first been detected. The soil was a
coarse alluvial sand grading ta fine silt, in which the
pesticide lindane (BHC) applied in previous years was
almost ail degraded. Soil samples were collected in
plastic food containers with snap-seal lids and trans-
ported ta the laboratary where !wo final instar GaIleria
mellonella larvae were placed on top of the soil. The
containers were inverted to keep the soil in intimate
contact with the larvae and left at room Temperature for
one week. After This time the larvae were removed and
retained on dry filter paper at room Temperature until
infective juvenile nematades emerged.
Although the concentration of grubs was high for
these species (about five per metre of row), it was tao low
for us ta obtain an indication of the level of parasitism
from the general survey. Therefore more intensive
sampling was conducted in four areas around sites
where infected grubs had been found during the general
survey. In these areas a trench was dug ta a depth of 1 m
along the row of cane until approximately 40 grubs were
collected (approx. 3 m 3). The grubs were transported ta
ISSN 1164-5571/92/01/71 03 $ 2.50/ © GaUlhier-Vi/lars - ORSTOM 71
R. J. Akhurst et al.
the laboratory in peat, disseeted and examined for_
nematodes.
Soil samples were taken from six other cane fields in
the Bundaberg district (five to fifteen samples per field)
and tested for the presence of entomopathogenic nema-
todes as described above.
The infectivity for third instar Lepidiota negatoria
larvae of entomopathogenic nematodes isolated during
this survey was tested by the method of Bedding et al.
(1983).
Results
Hundreds of dead grubs of four scarabaeid species
were seen during the sampling of the 5 ha of canefield
in which the epizootic occurred. However, the extent of
the area infected and the density of grubs present
indicate that tens of thousands of grubs may have been
infected. Very few inseets other than scarabaeids were
seen during the survey; none of these others were found
to be infected.
Infection rates of grubs of 26 %, 68 %, 90 % and 100 %
were recorded in the four samples of ca 40 grubs taken
by completely sampling portions of roWs. Sorne mem-
bers of each of the four grub species present were
infected : third instar larvae of Lepidioca crinita, L.
negawria and Lepidiola piClicol/is and pre-pupae and
pupae of Ancitrogus consanguineus.
Entomopathogenic nematodes were detected in 65 %
of the 236 soil samples (Fig. 1). Two species of en-
tomopathogenic nematode were recovered, both of the
genus Hecerorhabdicis. Infective juveniles of species
A (36 % of sampies) averaged 0.7 mm in length
(0.58-0.84 mm, n = 200) and carried an isolate of X.
luminescens that was not bioluminescent (Akhurst &
Boemare, 1986). Those of species B (32 %) averaged
0.59 mm in length (0.48-0.71 mm, n = 200) and carried
a luminescent isolate of X. luminescens. Isozyme analysis
(Akhurst, 1987) subsequently showed that species B was
conspecific with other Heterorhabdilis isolates obtained
from tropical regions (northem Australia, Cuba, south-
em China) and that species A is also an undescribed
species for which no other isolates are known.
Both species of nematode were detected in soil sam-
pies from a property adjoining that on which the epizo-
otic was discovered. Species A was not detected in
samples from six other properties in the district (6-30 km
distant) and species B from only one; none of the grubs
on any of these properties was found ta be infected.
When the original field was randomly sampled five
months later, only uninfected grubs were observed.
Species B was recovered from 26 % of soil samples but
species A from only 5 %.
The infectivity of bath Heterorhabdilis species for
third instar L. negawria in laboratory tests at 28 oC was
poor, with less than 50 % mortality at dosages up to
iO 000 nematodes/iOO ml sand.
72
~ L
·
0
·
0
· • 0 0
1
0
· •
g 0
1
• 0 0 0
1
0 0
1
0
• 0 ~ 0
· • 0 0 0 0 0 0
1
· • •
0 • 0 0
· • 0 0 0
·1 0
· • • 0 • 0 0
1
·
0 0 0 0 0
1
• 0
.
• 0 0 0
1g ·.0·0 •• gOOOO 000·
1
• • O·OQ
1
· • • 00·0 •,
• · • 0 .....,
• · • •
.·.gO 0
~
• 0 • .0 •• 0- 0
1
• 0 • • ·0· ·0 0
1
• • • • • ••• 0 0
1
• • 0 • •• 0.0 •
1
• • 0 • gO.·O •
• 0 • · ••. ·1 0
· • • ·.·.0 0
· •
.
• .g •• ·1 •
·0 L •
o HETERORHABDITIS sp A
• HETERORHABDITIS sp B
g HETERORHABDITIS spp A & B
• NO NEMATODES
Fig. 1. Distribution of Heterorhabditis spp. in three sugar cane
fields as determined by bioassay of soil samples.
Fundam. appl. NemalOl.
Discussion
As in an epizootic in white-fringed weevil, Grapho-
gnalhus leucoloma (Sexton & Williams, 1981), the epizo-
otic reported here involved Helerorhabditis infecting
insect species that were not very susceptible to infection
by any entomopathogenic nematodes under laboratary
conditions or in field trials, even with Sleinernema
glaseri, which has been found ta be the most effective
species (Bedding & Akhurst, unpub1.). Ir suggests that,
under suitable conditions, Helerorhabditis spp. can be
higWy effective against insect species previously thought
to be not amenable ta control by nematades. The in-
volvement of twO species of Helerorhabditis, neither of
which was very infective in subsequent laboratory as
says, suggests that conditions must have been particu-
larly suitable in the three fields in which the epizootic
occurred. Several factors may have contributed ta the
epizootic. The presence of four species of scarabaeid
with different life cycles may have provided an abundant
supply of susceptible hosts (e.g. early instars) over a
longer period than normal. The soil type and moisture
potential were highly suitable for the nematodes infec-
tivity (Molyneux & Bedding, 1984) and flooding of the
area sorne months previously may have aided their
dispersal. G. mellonella larvae used to bait the soil
samples were each infected by hundreds of nematodes,
suggesting that the nematodes were present in high
densities (Fan, 1989). The residual insecticide (BHC),
though largely degraded, may have had a slight debilita-
ting effect on the insects increasing their susceptibility to
nematode infection. It was not possible to de termine
which of these factors, or combination of factors, was
essential to the epizootic because there were no satisfac-
tory control blocks. The neighbouring field was not a
useful control because the sugar cane was in a different
period of the rotation, grub density was lower and the
field was elevated above the three in which the epizootic
occurred.
The difference in ratio of recovery of the twO Helero-
rhabditis spp. between the initial sampling and that of
five months later may indicate the better survival of
species B. Altematively, it may reflect differences in the
relative activity of the twO species at the time of testing,
as suggested by Fan's (1989) examination of Steiner-
nema feltiae (= S. bibionis) populations.
Although the epizootic reported here demonstrates
the potential of Helerorhabditis for controlling scara-
baeid larvae, it gave no clear indications of the most
effective means of using the nematodes in a control
program. The conditions required to establish an epi-
zootic of a particular pathogen can only be determined
by examination of the common features of a number of
such epizootics or by detailed experimental analysis of
factors that might be contributory.
Vol. 15, nO 1 - 1992
An epizoolic of Heterorhabditis spp.
References
AKHURST, R. ]. (1987). Use of starch gel electrophoresis in the
taxonomy of the genus Heterorhabditis (Nematoda : Hetero-
rhabditidae). Nemalologica, 33 : 1-9.
AKHURST, R. ]. & BEDDING, R. A. (1986). Natural occurrence
of insect pathogenic nematodes (Steinemematidae and
Heterorhabditidae) in soil in Australia. J. Ausl. enLOm. Soc.,
25 : 241-244.
AKHURST, R. ]. & BOEMARE, N. E. (1986). A nonlullÙnescent
strain of Xenorhabdus Iuminescens (Enterobacteriaceae). J.
gen. Microbi{)l.; 132 : 1917-1922.
AKHURST, R. ]. & BROOKS, W. M. (1984). The distribution of
entomophilic nematodes (Heterorhabditidae and Steiner-
nematidae) in North Carolina. J. Inverl. Palh., 44: 140-145.
BEAVERS, ]. B., McCoy, C. W. & KAPLAN, D. T. (1983).
Natural enellÙes of subterranean Diaprepes abbrevialus (Co-
leoptera : Curculionidae) in Florida. Env. Enlomol., 12 :
840-843.
BEDDING, R. A. & AKHURST, R. ]. (1975). A simple technique
for the detection of insect parasitic rhabditid nematodes in
soil. NemaLOlogica, 21 : 109-110.
BEDDING, R. A. & MOLYNEUX, A. S. (1982). Penetration of
insect cuticle by infective juveniles of Helerorhabditis
spp. (Heterorhabditidae: Nematoda). NemalOlogica, 21 :
109-110.
BEDDING, R. A., MOLYNEUX, A. S. & AKHURST, R. ]. (1983).
Helerorhabditis spp., Neoapleetana spp., and Sleinernema
kraussei : interspecific and intraspecific differences in in-
fectivity for insects. Exp. Parasit., 55 : 249-257.
FAN, X. (1989). Bionomics of a Brilish slrain of enlOmopalho-
genic nemalOdes (Sleinernemalidae). Ph. D. Thesis, Univer-
sity of London, 177 p.
MOLYNEUX, A. S. & BEDDING, R. A. (1984). Influence of soil
texture and moisture on the infectivity of Helerorhabditis sp.
DI and Sleinernema glaseri for larvae of the sheep blowfly,
Lucilia cuprina. NemalOlogica, 30 : 358-365.
MRAèEK, Z. & JENSER, G. (1988). First report of entomogen-
ous nematodes of the families Steinemematidae and Hetero-
rhabditidae from Hungary. Acta phyLOpalh. enl. hung., 23 :
153-156.
POINAR, G. O. Jr. (1979). NemalOdes for Biological Conlrol of
Insecls. Boca Raton, Florida, CRC Press, 227 p.
SEXTON, S. & WILLIAMS, P. (1981). A natural occurrence of
parasitism of Graphognalhus leucoloma (Boheman) by the
nematode Helerorhabditis sp., J. Ausl. en!. Soc., 20 :
253-255.
THOMAS, G. M. & POINAR, G. O. Jr. (1979). Xenorhabdus gen.
nov., a genus of entomopathogenic, nematophilic baeteria of
the family Enterobacteriaceae. Inl. J. SYSl. BaCleriol., 29 :
352-360.
73


An epizootic of Heterorhabditis spp. (Heterorhabditidae : Nematoda) in sugar cane scarabaeids (Coleoptera)

Abstract

Similar works

Full text

Available Versions

Horizon / Pleins textes