Ps. Grewal et al., Application of molluscicidal nematodes to slug shelters: A novel approach to economic biological control of slugs, BIOL CONTRO, 22(1), 2001, pp. 72-80
Slugs are a serious pest in floriculture, horticulture, and agriculture in
many parts of the world, and Deroceras reticulatum is generally the most de
structive species. A molluscicidal nematode, Phasmarhabditis hermaphrodita,
has potential for the biological control of pest slugs, but application ra
tes of 3.0 X 10(9) infective juveniles (IJs)/ha are usually required for ef
fective plant protection, rendering applications very expensive. The nemato
des are usually applied as an overall application to the surface of soil to
provide uniform coverage of the entire area. However, slugs possess a well
-developed homing behavior with an ability to locate homing sites or shelte
rs from over a meter away. As slugs are nocturnal foragers and spend signif
icant time in the homing sites during the day, we hypothesized that the app
lication of nematodes to the homing sites may be as effective as the overal
l application to the entire area. This hypothesis was tested in a newly des
igned bioassay arena consisting of 90 X 68 X 36-cm-deep plastic tubs mounte
d with copper slug barriers. Each tub contained muck soil to a depth of 15
cm, four Impatiens or Hosta plants, and 12 adult D. reticulatum slugs. The
nematode, P. hermaphrodita, was applied at 0.3 X 10(6) or 0.6 X 10(6) IJs/m
(2) either to the entire area or only under a 30 by 30-cm roofing shingle t
hat served as an artificial slug shelter. A standard chemical molluscicide,
metaldehyde, and an untreated control treatment were included for comparis
on. Although metaldehyde caused more rapid slug mortality than the nematode
s, the nematodes provided plant protection (i.e., number of leaves damaged
and leaf area eaten) equal or better than metaldehyde. Overall, the nematod
e application rate of 0.6 X 10(6) IJs/m(2) applied only under the shingles
provided equally or more effective plant protection than the application of
nematodes to the entire area at 0.3 X 10(6) IJs/m(2). This represents a 63
% reduction in the total number of nematodes required to treat the same are
a (i.e., 1.1 X 10(9) IJs/ha vs 3.0 X 10(9) IJs/ha). The additional presence
of recycled nematodes provided 96-100% control of the reintroduced slugs.
Even the low rate (0.3 X 10(6) IJs/m(2)) applied only under shingles was as
effective as the high rate (0.6 X 10(6) IJs/m(2)) applied as an overall tr
eatment to the entire area. We conclude that the application of P. hermaphr
odita to slug shelters may provide more economical control than the overall
application to the entire area. (C) 2001 Academic Press.