3. Damage caused by slugs
Terrestrial gastropods live in moist climate
They feed on leaves, stem, contaminating them with slime and
faeces
UK - 59 % crop damage in rapeseed
22 % in wheat crop
Deroceras reticulatum is the most common slug pest found in
garden areas
4. Introduction
Slug parasitic nematode – Phasmarhabditis hermaphrodita
It is a bacterial feeding rhabditid nematode
It kills slugs and snails
First isolated and documented by A . Schneider in 1859
P . hermaphrodita , P . papillosa , P . neopapillosa , P . californica ,
P . apuliae , P . bohemica , P . valida , P . bonaquaense ,P . nidrosiensis ,
P . tawfiki
First commercial biocontrol agent for terrestrial slugs ( Nemaslug® )
6. Associated bacteria – Moraxella osloensis
Mutualistic symbiont of P . hermaphrodita
It is found in the shell cavity of slug in which bacteria multiply and
kill the slug
Bacteria colonize the gut of IJ3
Once the bacteria is released inside the shell cavity IJ3 resume growth
Nematode feeds on the multiplying bacteria
Nematode colonizes the entire carcass
7. Chemical molluscicides
These cause damage to both beneficial and non – beneficial
non – target organisms ( mammals )
Metaldehyde
Iron phosphate
Carbamate ( methiocarb and thiodicarb )
8. Bio control
P . hermaphrodita are mass produced in fermenters upto 20,000 l in
monoxenic liquid broth of bacteria Moraxella osloensis
nematodes/ha
Applied at the rate of 3 × 109 nematodes/ha
Takes 1 – 3 weeks to kill slugs but equally or more effective at
killing slugs
It suppresses the feeding of infected slugs
Reported successful at reducing damage in winter wheat, lettuce,
rapeseed, strawberries, brussels, sprouts and asparagus
9. Effect of P . hermaphrodita on D . reticulatum
and young stages of Arion lusitanicus
Three different weight classes of young A . lusitanicus ( 0.15 g, 0.24 g,
0.45 g ) were exposed to dosage of 170 dauer larva/ g soil
monoxenically associated with the bacterium Moraxella osloensis
Group of 10 slugs were exposed to nematodes for 4 days
Transferred to petri-dish containing disc of Chinese cabbage as food
Food consumption was inhibited in both slug species
Slug mortality was recorded
10. Observations recorded from above experiment
D . reticulatum stopped feeding 6 days after the start of nematode
treatment
All weight classes of Arion lusitanicus feeding was reduced by 50
% only
The greatest reduction in feeding 90 % was noticed in the smallest
weight class ( 0.15 g )
11. Graph showing cumulative mortality of D . reticulatum and all
categories of A . lusitanicus ( 0.15 g, 0.24 g, 0.45 g ) treated with
P . hermaphrodita
0
10
20
30
40
50
60
70
80
90
100
5 6 7 8 9 10 11 12 13 14
D.reticulatum A. lusitanicus 0.15 g A. lusitanicus 0.24 g A. lusitanicus 0.45 g
Cumulative
mortality ( % )
Time in days
12. Conclusion
Nematodes successfully killed D . reticulatum, but were less
efficient at killing A . lusitanicus
Mortality was highest in D . reticulatum ( 98 % ) and the smallest
weight class of A . lusitanicus ( 47 % )
Almost no mortality in the largest weight-class of A . lusitanicus
Thus P . hermaphrodita associated with M . osloensis can be
considered as a biocontrol agent for young stages of A . lusitanicus
for its effect as a feeding inhibitor rather than for its ability to kill
the slugs
