concentrations of these ions in freshwater but less than the reported maximum natural concentra- tions. The ion toxicity for R. culicivorax (on a molar basis) ...
Meloidogyne in Sorghum: Orr, Morey 53 16. S I D D I Q U I , I. A., and D. P. T A Y L O R . 1970. Histopathogenesis of galls induced by
Meloidogyne naasi in wheat roots. J. Nematol. 2:239-247.
Salts and the Infectivity of Romanomermis culicivorax B. J. BROWN
and E. G. PLATZER ~
Abstract: T h e effects of c o m m o n inorganic ions f o u n d in freshwater on the infectivity of Romanomermis culicivorax and the survival of its host, Culex pipiens, were tested. In general, the median lethal concentrations found for R. culicivorax were greater t h a n the reported m e d i a n concentrations of these ions in freshwater b u t less t h a n the reported m a x i m u m n a t u r a l concentrations. T h e ion toxicity for R. culicivorax (on a m o l a r basis) increased in the following order: sodium < potassium < calcium; aml chloride < carbonate = sulfate < nitrate < nitrite < phosphate. T h e larvae of C. pipiens were generally 20 to 75 times as tolerant of h i g h e r ion concentrations as were the preparasitic stages of R. culicivorax. Key Words: Median lethal concentration, ion toxicity, m e r m i t h i d nematodes, mosquitoes, Culex pipiens.
T h e development of populations of pesticide-resistant mosquitoes and ecological and economic considerations related to the use of pesticides in aquatic environments have provided an impetus to the consideration of natural control. A vast array of mosquito pathogens are known (9), and the fungi and mermitifid nematodes hold the most promise for natural control of mosquito populations. Currently, the mermithids appear more promising since Petersen (12) has mass-reared one species, Romanomermis culicivorax Ross and Smith, and has demonstrated its efficacy in mosquito control. T h e ecology of R. culicivorax needs to be understood thoroughly for effective control of mosquito populations. Petersen (10, 11) has initiated studies of the effects of both density-dependent and densityindependent factors on the biology of R. culicivorax. T e m p e r a t u r e effects on the infectivity of R. culicivorax (2) were recently defined. Petersen and Willis (11) have found that natural infections of /~. culicivorax did not occur in Louisiana waters with conductivities greater than 350 micromhos/cm and that R. culicivorax was not infective in sodium chloride solutions with concentrations greater than 0.04 M. Received for publication 25 February 1977. 1Department of Nematology, University of California, Riverside, CA 92502. We thank Dr. J. J. Petersen (USDA, Lake Charles, Louisiana) for our starting cullures of R. culicivorax, and Dr. A. R. Barr (University of California at Los Angeles) for providing the autogenous strain of
Cule,¢ tJipiens.
Further development of R. culicivorax as a biological control agent requires determination of the tolerance limits of the infective stage to salinity derived from the various ions common in freshwater. T h e present investigation was designed to determine the effects of common ions found in freshwater on the infectivity of R. culicivorax for Culex pipiens L. M A T E R I A L S AND M E T H O D S A representative series of cations and anions common in freshwater were obtained by preparing solutions of 0.01 to 20 g of salt per liter distilled water from the following salts: NaC1, KC1, CaC12, Na~CO3, KzCO3, NaNO~, KNO3, Ca(NO~)2, NaNO~, KNO~, Na2SO4, K_~SO4, NaH2PO4 KH2PO4, and Ca(H2PO4)2. All salts were reagent grade. T h e p H and conductivity of each solution was measured before each experiment. Romanornermis culicivorax was propagated in Culex pipiens after procedures of Petersen and Willis (12). Used as the host for R. culicivorax was an autogenous strain of C. pipiens designated by Barr as 24g. All test solutions (125 ml) were placed in 200-ml polystyrene food containers, and 20 (-4-1) first-instar larvae of C. pipiens were added to each container (3 replications per salt concentration). Sixty ( ± 9 ) infective larvae of R. culicivorax, obtained by procedures described earlier (2), were added to each container. T h e containers were cov-
54 Journal o] Nematology, Volume 10, No. 1, January 1978 ered and placed in the dark at 27 C. After 24 h, the infective period was terminated by pouring the contents of each container into a sieve (180-/~m openings). T h e mosquitoes were washed off the sieve, returned to clean containers with 125 ml water, fed, and left at 27 C for 10 days (2). T h e n the n u m b e r of postparasitic nematodes and adult mosquitoes in each container was determined. T h e percentage of postparasites recovered was based on the calculated number of preparasitic larvae added (2). Four experiments were carried out. Seven concentrations (20, 10, 2.5, 1.0, 0.5, 0.25, and 0.1 g/liter) of each of the 15 salts were used in the first three experiments. T h e r e were two groups in each experiment: one group tested the response of the mosquito larvae alone, and the other tested the response of the infective nematode larvae and mosquito larvae to the salts. T h e fourth experiment involved 10 concentrations of each salt (10, 5, 2.5, 1.0, 0.5, 0.25, 0.1, 0.05, 0.025 and 0.01 g/liter). T h r e e experimental groups were studied: the first two were as in the first three experiments, and the third group tested the infectivity of nematode larvae preexposed to the salts for 4 h before the mosquito larvae were placed in the infection containers. T h e data from the four experiments were pooled, and median lethal concentrations of the salts for mosquito larvae and infective nematode larvae were calculated by probit analysis (3, 4, 5).
RESULTS T h e salt effects were compared first on the basis of the m a x i m u m salt concentrations at which some mosquito survival and nematode infections occurred. T h e salts least toxic to the mosquitoes were sodium sulfate and potassium sulfate, in which some survival occurred even at 20,000 m g / l i t e r (Table 1). T h e most toxic salts to the mosquitoes were sodium nitrite and potassium nitrite, in which there was no survival above 1,000 rag/liter. Mosquitoes survived over a p H range of 3.4 to 10.5. T h e m a x i m u m conductivity allowing some mosquito survival was 20,000 micromhos per cm. Nematodes retained infectivity, albeit at low levels, in 7 salts: sodium chloride, calcium chloride, sodium nitrate, potassium nitrate, calcium nitrate, potassium sulfate, and potassium phosphate, to concentrations of 2,500 m g / l i t e r (Table 2). Infectivity was retained over a p H range of 3.6 to 8.6. T h e highest conductivity at which infection was achieved was 4,000 micromhos/cm. A comparison of the m a x i m u m levels of mosquito survival (Table 1) and nematode infection (Table 2) showed that in all but two salts (potassium nitrite and potassium nitrate) the mosquitoes were more salttolerant than the nematodes (Fig. 1). W h e n the m a x i m u m levels at which infection occurred with mosquitoes and nematodes added simultaneously to the salt
TABLE !. Maximum salt tolerances o1 the first-instar larvae of Culex pit)iens.a
Salt NaC1 CaCI~ KCI Na2CO3 K2CO~ Na2SO4 K2SO4 NaNO3 Ca(NOa)2 KNO~ NaNO2 KNO~ NaHzPO~ Ca(H~PO4)2 KH2PO4
Concentration mg/liter mM 10,000 10,000 10,000 5,000 2,500 20,000 20,000 5,000 10,000 2,500 1,000 1,000 I0,000 2,500 10,OO0
171 90 134 60 24 141 115 59 610 25 15 12 83 11 74
pH 5,9 6.3 6.2 10.5 10.3 6.0 5.9 5.6 5.9 5.4 6.1 6.5 4.6 3.4 4.5
Conductivity (micromhos/cm)
Percent survival
16,000 12,200 16,000 6,800
40 32 23 5
3,550
3
18,000 20,000 5,750
2 5 10
8,000
3
3,050 1,525 1,520 5,200
13 2 8 18
1,220
2
6,100
2
•The maximum salt concentrations at which survival of mosquito larvae occurred.
Salinity Effects on R, culicivorax: Brown, PIatzer 55 T A B L E 2. M a x i m u m salinity tolerances of t h e preparasitic larvae of R o m a n o m e r m i s Concentration rag/liter mM
Salt NaC1 CaCI 2 KC1 Na2CO 3 K~CO 3 NaNO 3 Ca(NO3) 2 KNO 3 NaNO 2 KNO 2 Na2SO 4 K2SO 4 NaFI2PO 4 Ca(H2PO4) 2 KH~PO 4
2,500 2,500 500 250 250 2,500 2,500 2.500 500 1,000 500 2,500 1,000 1,000 2,500
43 23 7 3 2 28 15 25 7 12 4 14 8 4 18
culicivorax. ~
pH
Conductivity (micromhos/cm)
Percent survival
5.5 5.8 5.4 8.6 8.5 5.4 5.7 5.4 6.4 6.5 5.5 5.5 4.7 3.6 4.5
4,400 3,460 730 385 370 3,030 1,825 3,050 635 1,520 620 3,300 620 630 1,675
1 1 5 1 1 l 1 1 1 1 7 1 1 1 3
• T h e m a x i m u m salt c o n c e n t r a t i o n s at w h i c h infectivity occurred.
solutions were c o m p a r e d with the m a x i m u m infection levels resulting when mosquitoes were not added until the nematodes had been exposed to the salt solutions for 4 h, no change was found in the m a x i m u m concentration at which some infection occurred for seven of the salts tested (Fig. 2). Four hours of previous exposure substantially re20000
,oooo t:~
5000
E 2500 ",..~__.
*~ ,ooo cO
500
o
250
tO0
££
-
0o ~ oo -o
o~°~ zo~ oo z
zo
ZCD~:
Z
Z
v
Z(J~:
0"6"," V
Z~:
Z
~
® FIG. 1. C o m p a r i s o n of t h e m a x i m u m salt conc e n t r a t i o n s at w h i c h m o s q u i t o e s survived a n d n e m a t o d e s were infective. C o n c e n t r a t i o n s for mosquitoes a n d n e m a t o d e s are e q u a l for KNO:~ a n d K N O 2. O p e n bars, m o s q u i t o survival; cross h a t c h , n e m a t o d e infectivity; c o n c e n t r a t i o n p l o t t e d on a l o g a r i t h m i c scale.
duced the m a x i m u m concentration at which the nematodes were infective in the remaining eight salts [NaCI, CaC12, Ca(NO~) 2, N a N O 2 , K 2 S O 4, N a H 2 P O 4, C a ( H 2 P O 4 ) 2, and KH2PO4]. Subsequent data analysis was based on the individual ions in each salt experiment, so that the effects of tile counterions could be determined ( T a b l e 3, 4, Fig. 2-10). All calculations were on a m g / l i t e r basis for each ion, so that average concentrations for m a x i m u m tolerance and m e d i a n lethal concentrations could be calculated for each series of counterions, e.g., sodium cation in the presence of tile 6 anions tested. T h e average m a x i m u m ion tolerances of the mosquito larvae were calculated (Table 3, 4) b u t it was necessary to recalculate the concentration of each ion as a molarity to compare the average effects of each ion within its ion class. T h e m a x i m u m tolerance for cations in order of decreasing tolerance was: sodium, 86 raM; potassium, 63 raM; and calcium, 54 raM. In the median-lethal-concentration series, however, the order of calcium a n d potassium changed: sodium, 50 raM; calcium, 19 raM; and potassium, 15 m M . T h e m a x i m u m tolerance for anions in order of decreasing tolerance was: chloride, 132 raM; sulfate, 128 raM; phosphate, 56 raM; nitrate, 36 m M ; carbonate, 33 raM; a n d nitrite, 13 mM. T h e order of carbonate and nitrite changed in the median-lethal-concentration series: chloride, 112 raM; sulfate, 54 raM;
Journal of Nematology, Volume 10, No. 1, January 1978
56
T A B L E 3. M a x i m u m cation tolerance a n d m e d i a n lethal c o n c e n t r a t i o n s for t h e first-instar larvae of
Culex pipiens. Anion present
M a x i m u m conc. tolerated
Na ÷
CICOa = NO Z N O 2SO4 = H ~ P O 4mean
3,930 1,085 1,355 333 3,240 1,920 1,977
3,230 133 55 10 1,244 572 1,157
Ca ++
C1N O 8H2PO.~mean
3,600 2,400 428 2,156
2,129 69 29 742
633-20,000 +
CICOa = NO Z N O 2SO Z H 2 P O 4mean
5,240 708 968 459 4,490 2,870 2,456
2,692 49 145 35 501 41 644
896-20,000 + 15-91 74-238 3-76 210-998 0-161 200-20,000 +
Cation
K+
LCs0 (mg/liter)
95% CL •
1,832-16,466 58-261 14-109 2-20 788-2,463 0-9,717 669-4,538 1-217 ll-fi0
215-20,000 +
"Confidence limits for m e d i a n lethal concentrations. T A B L E 4. M a x i m u m a n i o n tolerance a n d m e d i a n lethal c o n c e n t r a t i o n s for the first-instar larvae of
Culex pipiens.
Anion
Cation
M a x i m u m conc. tolerated
C1-
Na ÷ Ca ++ K+ mean
6,070 3,200 4,760 4,677
4,907 1,893 2,445 3,984
CO3 =
Na + K÷ mean
2,830 1,085 1,958
348 49 212
152-680 15-91 84-386
NO Z
Na + Ca ++
3,645 3,780
38-293 1-336 117-377 52-335 4-40 3-90 4-65
LC.~0 mg/liter)
K+
1,533
mean
2,986
147 107 230 161
NO~-
Na + K÷ mean
666 541 604
20 41 31
SO4 =
Na + K+ mean
13,520 11,020 12,270
5,192 198 2,695
H 2 P O 4-
Na + Ca ++ K+ mean
8,080 1,036 7,170 5,429
2,407 71 103 860
• Confidence limits for m e d i a n lethal concentrations.
95% CL ~
2,782-20,000 + 563-20,000 + 814-20,000 + 2,089-20,000 +
3,247-10,278 83 -395 1,665-5,337 0-20,000 + 26-120 0-402 9-13,805
S a l i n i t y Effects on R . culicivorax: Brown, Platzer 57
I000 800 600
--
A
I00
B
80 i
~
6o
400
200 0
..... ~ _ ~, ~ , ,~o,~
@ 0
oooo~
',-)Z Z.cO'I- Ix
o,~ ~
o~ o~ o~ ~ (o
Z
Na
I0001 _
(~
%
(,") -I- ,x
Na
A
I001
400
B
40
01 =~ • --
Z
0
~z'r,x
~
Ca
z
:~,x
Ca
(D A
B
140
120
I000
I00
8001
~
80 ,o
0
O; _
C.)C.) Z Z O~-r'~× K
@ ~
o 0
o
c~c/
Z
Z
O')
"I- ,~
K
FIG. 2-4. TQlcrance of Romanomermis culicivorax to cation concentrations (mg/liter _ 95% confidence limits). Cation ca~ncentrations in freshwater, median (-- -- --) and maximum ( . . . . ). 2) Sodium. 3) Calcium. 4) Potassium. A) is the ulaximum tolerance, and B) is the median lethal concentration.
58 Journal o[ Nematology, Volume i0, No. 1, January 1978 phosphate, 8.9 raM; carbonate, 3.5 raM; nitrate, 2.1 raM; and nitrite, 0.67 raM. T h e toxicity of cations for the infective larvae of R. culicivorax was altered greatly by the anion present. Cation toxicity was lowest in the presence of chloride anions, and the toxicity was greatly increased in the presence of phosphate or nitrite anions (Fig. 2-5, 8, 10). C o m p a r i s o n of tile cation effects in Fig. 2-4 showed the same relative effects of the anions with each cation. In general, the m e d i a n lethal concentrations for the infective larvae of the cations and anions studied were greater than their levels as reported for freshwaters of N o r t h America, though less than the m a x i m u m concentrations found (16) (Fig. 2-4, 9). T h e m a x i m u m tolerated concentrations of cations for the infective larvae were similar: sodium, 16 m M ; calcium, 14 m M ; and potassium, 13 raM. A different cation order existed, however, in the medianlethal-concentration series: sodium, 1.04 m M ; potassium, 0.74 m M ; and calcium, 0.42 raM. T h e m a x i m u m tolerated concentrations of anions for the infective larvae were, in order of increasing toxicity: chloride, 24 mM; nitrate, 18 m M ; phosphate, 10 m M ; nitrite, 9.5 m M ; sulfate, 8.9 m M ; and carbonate, 2.1 raM. On the basis of m e d i a n lethal concentrations, however, a substantial reordering occurred in calculation of the anion order: chloride, 1.9 m M ; carbonate, 0.85 m M ; sulfate, 0.81 m M ; nitrate, 0.44 m M ; nitrite, 0.37 raM; and phosphate, 0.12 mM.
B
180
16o
,6oo _ 1400
140
,zoo
120
~ooo soo 600 400 20o
~l
]
20
~ ?'ct~ '* A
c .~
~ o c o -~ ,~
Cl
,oo1
:0 A 400[ 200
v
o ~-~,* c% 2ooo ,0oo ,600 ~40o I ~zo0
® co 3
A
B
160 140
J20
~
ioo
,ooo
800 60o
80 60 4o
4°°1 200| o k.
o o o z ~
DISCUSSION I n this investigation, salt tolerances of the preparasites were d e t e r m i n e d by simultaneous exposure of b o t h preparasites and hosts to various salt concentrations for 24 h. T h a t procedure a p p e a r e d to be a satisfactory simulation of field releases of preparasitic nematodes into freshwater of varying salt content since the majority of the preparasites of R. culicivorax penetrate the available mosquito hosts within 24 h (2, 10) under laboratory conditions and in field studies. In general, the first-instar larvae of C. pipiens were m o r e tolerant of the salts tested than were the infective larvae of R.
@
.
*C 0
.......
NO3
~
ix
NO3
FIG. 5-7. Tolerance of Romanomermis culicivorax to anion concentrations (mg/li.ter ± 95% confidence limits). 5) Chloride; concentrations in freshwater, median (-- -- --) and maximum (. . . . ). 6) Carbonate; typical concentration in freshwater (. . . . ). 7) Nitrate; typical nitrate concentration in freshwater (-- -- --). A and B as in Fig. 2-4.
culicivorax. C o m p a r i s o n of the m e d i a n lethal concentrations for mosquito and nematode larvae showed that, for most cations and anions, the mosquito larvae tolerated ion concentrations 20 to 74 times those tolerated by the n e m a t o d e larvae. T h e respective average concentrations of nitrite, nitrate, and carbonate tolerated, however, were only 2, 4, and 5 times those tolerated
Salinity Effects on R. culicivorax: Brown, Platzer 59 by the nematode larvae. W i t h nitrite in the presence of potassium, the median lethal concentration for the nematode larvae showed a combined deleterious effect on both the infective parasite and the host. Further determination of the median lethal concentration of nitrite in the presence of potassium for the infective larvae would require a host with greater tolerance for this salt. T h e median concentrations (rag/liter) for the ions found in 90% of the freshwaters in N o r t h America are: sodium and potassium combined, 10; calcium, 9; and sulfate, 32 (16). T h e m a x i m u m concentrations (rag/liter) found for those ions are: sodium and potassium combined, 85; calcium, 52; chloride, 170; and sulfate, 90 (6, 16). A typical lake may contain carbonate at 38 rag/liter, whereas 1 rag/liter is typical for spring water. Nitrate is found in low concentrations (1 rng/liter) in normal groundwater, whereas many water supplies contain 14 rag/liter and feedlot runoff may contain 83 mg/liter. Nitrite concentrations are not listed in the literature for natural waters but are always lower than the nitrate concentrations in the water source (6, 16). Normal phosphate concentrations are 1 rag/liter, whereas wastewater from fertilizer plants can contain as m u c h as 30 rag/liter (6). T h e median lethal concentrations obtained for R. culicivorax are generally greater than the median concentrations of the common ions in freshwater of N o r t h America, indicating that 2~. culicivorax can be used successfully in most freshwater in N o r t h America. Elevated calcium concentrations and nitrite levels, however, would restrict its use. Elevated phosphate levels would be detrimental b u t would probably occur only in unusual situations, e.g., effluents from fertilizer plants. Several investigators have studied the effects of salts on nematode survival, motility, and metabolism. Walker (15) reported that populations of Pratylenchus penetrans decreased in soil following the addition of nitrate, nitrite, organic nitrogen, and amm o n i u m compounds. Nitrate was the least nematicidal, and nitrite the most. Similarly, nitrite inhibited the infectivity of R. culicivorax more than did nitrate. Stephenson (13) found that increasing salt
8
~°°I
°°°IFI 1'1o2
NO2
B 16o
cO ,4--
C (D 0 C 0
1400
14.0
1200
12o
I000
I00
8OO
8o
6OO
6o
4OO
4O
2OO
c)
®
0
cO c--
Z~tx
so4
so4
,2000 1800 1600 1400 1200 I000 8OO
8O
60O 40O
4O
2O0 0
H2Po4
H2PO4
F I G . 8-10. T o l e r a n c e of Romanomermis culicivorax to a n i o n c o n c e n t r a t i o n s ( n a g / l l t e r + 9 5 % confidence limits). 8) N i t r i t e . 9) Sulfate; m a x i m u m ( . . . . ) a n d m e d i a n (-- -- --) c o n c e n t r a t i o n s of sulfate i,n f r e s h w a t e r . 10) P h o s p a t e ; m a x i m u m c o n c e n t r a tion in f r e s h w a t e r ( . . . . ). A a n d B as in Fig. 2-4.
concentration caused body shrinkage and cessation of movement in Rhabditis terrestris, and the rates of penetration could be arranged as follows: KCI, MgCI2 < CaC12 < NaC1. Other investigations of salt effects have been carried out on animal-parasitic nematodes. Von Brand (15) studied the
60 Journal o] Nematology, Volume 10, No. 1, JanuaTy 1978 effects of salts o n the o x y g e n c o n s u m p t i o n of Eustrongylides ignotus, a n e m a t o d e p a r a s i t e o f fish. O f t h e salts tested, o n l y N a N O 2 ( a n d KC1 to a lesser degree) w e r e toxic. I n t e r e s t i n g l y , the o x y g e n c o n s u m p t i o n o f E. ignotus was s t i m u l a t e d b y v a r i o u s ions a c c o r d i n g to the f o l l o w i n g series: cations -- sodium = magnesium < calcium = ammonium < potassium; anions chloride = sulfate < nitrite = nitrate < p h o s p h a t e . T h a t series is s i m i l a r to series f o u n d for R. culicivorax. B u e d i n g (1) f o u n d t h a t h i g h c o n c e n t r a t i o n s of K C I a n d CaC12 markedly decreased the metabolic activity a n d m o t i l i t y of Litosomoides carinii, a f i l a r i o i d f r o m c o t t o n rats. M o s t i n f o r m a t i o n a v a i l a b l e o n t h e salt t o l e r a n c e s of f r e s h w a t e r a n i m a l s d e a l s w i t h a r t h r o p o d s a n d v e r t e b r a t e s . T h e salt tolerances of a free-living t u r b e l l a r i a n , Polycelis nigra, h a v e b e e n i n v e s t i g a t e d , a n d the o r d e r of c a t i o n a n d a n i o n t o x i c i t i e s was s i m i l a r to t h e averages r e p o r t e d for R. culicivorax (7, 8). A l t h o u g h J o n e s (7, 8) f o u n d c a t i o n s m o r e toxic t h a n a n i o n s , t h e a v e r a g e t o x i c i t y of the c o m m o n f r e s h w a t e r a n i o n s a n d c a t i o n s was e q u i v a l e n t for t h e i n f e c t i v e stage o f R. culicivorax. T h e m e c h a n i s m b y w h i c h t h e ions affected t h e i n f e c t i v i t y of R. culicivorax was n o t d e t e r m i n e d . T h e t o x i c i t y at e l e v a t e d ion concentrations may have resulted from: 1) i n c r e a s e d o s m o t i c p r e s s u r e a n d conc o m i t a n t w a t e r loss f r o m the n e m a t o d e s ; 2) i m b a l a n c e i n i n t e r n a l i o n b a l a n c e ; 3) g e n e r a l t o x i c effects of n i t r a t e s a n d n i t r i t e s ; a n d 4) a l t e r e d i n t e r n a l acid-base b a l a n c e . I t m a y b e s p e c u l a t e d that, as w i t h E. ignotus (14), a n i n c r e a s e i n m e t a b o l i c r a t e s t i m u l a t e d b y salts m a y h a v e e x h a u s t e d the e n e r g y resources of t h e i n f e c t i v e stages b e f o r e the h o s t was c o n t a c t e d , t h e r e b y reducing the infective potential of the n e m a t o d e . I n a d d i t i o n , the d e c r e a s e d b o d y w a t e r of n e m a t o d e s at h i g h salt concent r a t i o n s w o u l d p r o b a b l y decrease t h e i r motility and, thereby, infectivity. At the salt c o n c e n t r a t i o n s o b t a i n e d for m e d i a n l e t h a l c o n c e n t r a t i o n s , h o w e v e r , the m o s t l i k e l y e x p l a n a t i o n is t h a t i o n i m b a l a n c e s o c c u r r e d in t h e i n f e c t i v e n e m a t o d e s a n d that the ensuing metabolic disruptions i n t e r f e r e d w i t h t h e i n f e c t i v e a b i l i t y of the preparasites. Those questions will be the subject of future investigations.
A c t u a l field s i t u a t i o n s d o n o t h a v e w a t e r s c o n t a i n i n g o n l y single c a t i o n s o r anions, and further work approximating a c t u a l field c o n d i t i o n s is necessary to d e t e r m i n e t h e effects of c o m b i n a t i o n s o f ions o n the i n f e c t i v e a b i l i t y o f R. culicivorax. A n o t h e r i n t e r e s t i n g f e l d for f u t u r e s t u d y is t h e effects of salts o n o t h e r life-cycle stages to d e t e r m i n e the effects of s a l i n i t y o n t h e a b i l i t y of R. culicivorax to r e p r o d u c e o n a c o n t i n u i n g basis in a b o d y of w a t e r a f t e r p r e l i m i n a r y a p p l i c a t i o n s of p r e p a r a s i t e s . P r e l i m i n a r y studies i n this a r e a i n d i c a t e that adult nematodes are more salt-tolerant than are preparasites. LITERATURE
CITED
1. BUEDING, E. 1949. Studies on the metaholism of the filarial worm Litomosoides carinii. J. Exp. Med. 89:107-130. 2. BROWN, B. J., and E. G. PLATZER. 1977. The effects of temperature on the infectivity of Romanomermis culicivorax. J. Nematol. 9:166172. 3. FINNEY, D. J. 1949. The adjustment for a natural response rate in probit analysis. Ann. App1. Biol. 36:187-195. 4. FINNEY, D. J. 1952. Probit analysis. 2d ed. Cambridge University Press. 318 p. 5. FISHER, R. A., and F. YATES. 1957. Statistical tables for biological, agricultural and medical research. 5th ed. Oliver and Boyd. 148 p. 6. GEOLOGICAL SURVEY WATER SUPPLY PAPER 1473. 1970. Study and interpretation of the chemical characteristics of natural water. 269 p. 7. JONES, J. R. E. 1940. A further study of the relation between toxicity and solution pressure, with Polycelis nigra as test animal. J. Exp. Biol. 17:408-415. 8. JONES, J. R. E. 1941. A study of the relative toxicity of anions with Polycelis nigra as test animal. J. Exp. Biol. 18:170-181. 9. LEGNER, E. F., R. D. SJOGREN, and I. M. HALL. 1974. The biological control of medically important arthropods. CRC Crit. Rev. Envirn. Cont. 4:85-113. 10. PETERSEN, J. J. 1973. Role of mermithid nematodes in biological control of mosquitoes. Exper. Parasitol. 33:239-247. 11. PETERSEN, J. J., and O. R. WILLIS. 1970. Some factors affecting parasitism by mermithid nematodes in Southern house mosquito larvae. J. Econ. Entomol. 63:175-178. 12. PETERSEN, J. J., and O. R. WILLIS. 1972. Procedures for the mass rearing of a mermithid parasite of mosquitoes. Mosq. News 32:226-230. 13. STEPHENSON, W. 1944. The effect of certain inorganic chloride solutions upon the movement of a soil nematode (Rhabditis terrestris), and upon its body size. Parasitology 35:167-172.
Salinity Effects on R. culicivorax: Brown, Platzer 61 14. VON BRAND, T. 1943. Physiological observations u p o n a larval Eustrongylides. iV. Influence of temperature, p H and inorganic ions u p o n the oxygen c o n s u m p t i o n . Biol. Bull. 84:148-156. 15. W A L K E R , J. T. 1971. Populations of Pratylen-
cfius penetrans nitrogenous soil 3:43-49. 16. W A R R E N , C. E. pollution control. 434 p.
relative to decomposing amendments. J. Nematol. 1971. Biology and water W. B. Saunders Company.
Criconematinae Habitats and Lobocriconema thornei n. sp. (Criconematidae:Nematoda) ~ NATALIE K N O B L O C H a n d G. W. BIRD 2 Abstract: A 16.4-ha arca at the Michigan State University Water Quality Research Site was surveyed to obtain information on the habitats and p r o m i n e n c e of taxa of the Criconematinae. Fifteen species representing six genera (Macroposthonia, Lobocriconema, Criconema, Crossonema, Nothocriconema, and Xenocriconemella) of this subfamily were recovered from the e x p e r i m e n t a l site. Species occurrence and p o p u l a t i o n densities were evaluated by using p r o m i n e n c e and importance values. T h e Criconematinae was one of the most p r o m i n e n t and i m p o r t a n t nematode subfamilies recovered from this area. T h e species successfully inhabited a broad range of woodlot and field vegetations, and soil m a n a g e m e n t groups. T a x a of the Criconematinae were generally m o r e p r m n i n e n t in woodlot than in field vegetations, a l t h o u g h with several i m p o r t a n t exceptions, especially w i t h i n the genus Macroposthonia. T h e second-most p r o m i n e n t and i m p o r t a n t species recovered was an tandescribed species of Lobocriconerna. It is described as Lobocriconema thornei n. sp., including scanning electron micrographs of females, and descriptions of several of the juvenile stages. Key Words: Ecology, Macroposthonia, Lobocriconema, Criconema, Crossonema,
Nothocriconem.a, Xenocriconemella.
Little is known about the biology of the Criconematinae. T h e literature was recently reviewed by Hoffman (8). Some species are cosmopolitan, whereas others are less widely distributed and appear to be associated with specific habitats. All species o[ the Criconematinae are assumed to be parasites of higher plants, and some have been shown to be pathogens. Macroposthonia xenoplax can be a predisposition agent (13). A limited n u m b e r of observations have been made about relationships of species o1 the Criconematinae with soil moisture, temperature, pH, and texture (1, 7, 8, 11, 12, 14, 15, 16, 18). This project was done to evaluate species of tile Criconematinae in relation to their habitats and other stylerbearing nematodes in a 16.4-ha area in Received for publication 23 May 1977. t Project supported in part by the Water Quality Management Project, Institute of XVater Research, Michigan State Unisersity, East Lansing 48824. Published as Michigan Agricultural Experiment Station Journal Series Article No. 8116. Sincere appreciation is expressed to Mr. John Davenport, Mr, Jose Verlarde, and Dr. John Knierim for assistance in collecting and processing the soil samples; Dr. S. Stevenson for the vegetation data; and Dr. L. Robertson for the soil data. 2Nematode taxonomist and professor, respectively, Departmerit of Entomology, Michigan State University, East Lansing, MI 48824,
central
Michigan.
A
new
species
of
Lobocriconema was recovered from the experimental site and is described herein. M A T E R I A L S AND M E T H O D S A d6.4-ha (671 x 2"t4 m) area at the Michigan State University Water Quality Research Site was selected for a survey of nematode species and determination of their population densities. T h e site was divided into II0 experimental units (Fig. 1). Sixty-six of the plots were 0.186 ha (61.0 x 30.5 m) in size, and 44 were 0.093 ha (30.5 x 30.5 m). Forty-eight percent of the area consisted of forests (Fig. 1 A-C), 40% old fields (Fig. 1 D-E), and 9% second-growth shrubland (Fig. l-F). T h e following is a general vegetation description of the area:
Forest A: Sugar maple, beech, elm, red maple, and basswood (75, 10.7, 4.5, 3.9, and 2.2% dominance, respectively, in 10-cm size class (trunk diameter), with 422.9 trees/ha and a mean basal area of 41.6 m2/ha), and sugar maple, elm, Ostrya sp., red maple, and black maple (30.7, 24, 14, 7.9, and 7.9% dominance,
