160
14. WALOBF
Parasitism in the Leucupteru populations at Silwood Park was probably one of the most important factors in checking its numbers. Tetrastichw sp. nr. gahtopwr (Ratz.) (Eulophidae) waa the most abundant
and effective parasite. Its life cycle waa perfectly synchronised with
that of the host and in 1966-66 more than half (67.7%) of the pupal
population of Lewpteru was destroyed by it. This high incidence of
parasitism followed on a year of great density of Lewqtera in Area 4.
The population budgets (Table XXXIII) show that heavy mortalities
occur in the fifth and sixth larval and in the pupal instars and these
stages are the most heavily attacked by the parasites. Tetrastichus
attacks the fist instar larvae, but does not kill the host until the pupal
stage. Thus it has been wrongly described as the parasite of the pupal,
or of the cocoon stage (Frick, 1964; Parker, 1964).
The other four hymenopterous parasites me Necremnus sp. (Eulophidae) which attacks the fifth instar larvae about to moult, Chrysockaris
gemma (Walker) (Eulophidae) and Pringalio soemias Walk. which
attack the sixth instar larvae in mines, and Necremnws meialtzrus Walk.
which attacks the larvae in cocoons. Percentages of parasitism are given
in Table XXXVI and that of Tetrastichus is based on dissections of
the pupae.
TABLE XXXVI
Paraitism of Leucoptere l a m and pupae (After Agwu, 1967)
Paxasite
yo Parasitism
1964
1966
1966
Necrernnua sp. (Illarch-April)
0.8
2.8
1.9
Chsyeocha& (May)
14.9
11.1
2 7 4
Pnigdio (April-May)
1.1
1 -4
6.5
Neurmnus metakmcr, (Juneduly)
9.6
114
19-2
Tekaatichw (Junduly)
13.7
28.0
67 -7
Agwu considers that there rn strong indications that the high larval
parasitism, especially that of Tetrastichus may have a regulatory effect
on Leucoptera populations.
(iii) Larval atages within the mines are well protected from many
arthropod predators, but birds slit open the mines and remove the
caterpillars. Hering (1961) said that ‘‘birds are the main enemies of
mining insects in Europe since they peck out larvas and pupae from
mines”. The slit mines are easily identifiable and estimatea were made
of the totals of sixth instar larvae destroyed by birds in the three seas o n ~ (Table XXXVII). It is possible that bird predation was of the
14. WALOBF
Parasitism in the Leucupteru populations at Silwood Park was probably one of the most important factors in checking its numbers. Tetrastichw sp. nr. gahtopwr (Ratz.) (Eulophidae) waa the most abundant
and effective parasite. Its life cycle waa perfectly synchronised with
that of the host and in 1966-66 more than half (67.7%) of the pupal
population of Lewpteru was destroyed by it. This high incidence of
parasitism followed on a year of great density of Lewqtera in Area 4.
The population budgets (Table XXXIII) show that heavy mortalities
occur in the fifth and sixth larval and in the pupal instars and these
stages are the most heavily attacked by the parasites. Tetrastichus
attacks the fist instar larvae, but does not kill the host until the pupal
stage. Thus it has been wrongly described as the parasite of the pupal,
or of the cocoon stage (Frick, 1964; Parker, 1964).
The other four hymenopterous parasites me Necremnus sp. (Eulophidae) which attacks the fifth instar larvae about to moult, Chrysockaris
gemma (Walker) (Eulophidae) and Pringalio soemias Walk. which
attack the sixth instar larvae in mines, and Necremnws meialtzrus Walk.
which attacks the larvae in cocoons. Percentages of parasitism are given
in Table XXXVI and that of Tetrastichus is based on dissections of
the pupae.
TABLE XXXVI
Paraitism of Leucoptere l a m and pupae (After Agwu, 1967)
Paxasite
yo Parasitism
1964
1966
1966
Necrernnua sp. (Illarch-April)
0.8
2.8
1.9
Chsyeocha& (May)
14.9
11.1
2 7 4
Pnigdio (April-May)
1.1
1 -4
6.5
Neurmnus metakmcr, (Juneduly)
9.6
114
19-2
Tekaatichw (Junduly)
13.7
28.0
67 -7
Agwu considers that there rn strong indications that the high larval
parasitism, especially that of Tetrastichus may have a regulatory effect
on Leucoptera populations.
(iii) Larval atages within the mines are well protected from many
arthropod predators, but birds slit open the mines and remove the
caterpillars. Hering (1961) said that ‘‘birds are the main enemies of
mining insects in Europe since they peck out larvas and pupae from
mines”. The slit mines are easily identifiable and estimatea were made
of the totals of sixth instar larvae destroyed by birds in the three seas o n ~ (Table XXXVII). It is possible that bird predation was of the