Jul 21, 2017 - mean survival of nymphal and adult stages of Monelliopsis pecanis Bissell ... observed, with the greatest mortality being at the extreme high (37 ...
POPULATION
ECOLOGY
Survival of Yellow Pecan Aphids and Black Pecan Aphids (Homoptera: Aphididae) at Different Temperature Regimes WALID KAAKEH AND JAMES D. DUTCHER Department of Entomology, University of Georgia, Coastal Plain Experiment Station, Tifton, GA 31793
Environ. EntomoJ. 22(4): 810-817
(1993)
ABSTRACT Constant high temperature regime (30, 34, 37, and 40°C) for 1-5 h decreased mean survival of nymphal and adult stages of Monelliopsis pecanis Bissell and Melanocallis caryaefoliae (Davis) with increasing temperature and time of exposure. Constant low-temperature regime (0, 6, 12, and 15°C) decreased aphid survival with decreasing temperatures and increasing time of exposure. A temperature by aphid interaction was observed, with the greatest mortality being at the extreme high (37 and 40°C) and low (O and 6°C) temperatures. Aphid stages showed differences in tolerance to all temperature levels. Third and fourth ins tars and adults of both species withstood a wide range of temperatures better than first and second instars under either regime. M. pecanis tolerated low temperatures better than M. caryaefoliae, but at high temperatures, M. caryaefoliae was more tolerant. Air temperature fluctuations within a pecan tree were measured during July with temperature probes. Air temperature was slightly higher at the edge of the tree crown than near the trunk, otherwise temperatures were very uniform within the tree crown for a given hour of the day. KEY WORDS
Monelliopsis
pecanis, Melanocallis
YELLOW PECAN APHID, Monelliopsis pecanis Bissell, and the black pecan aphid, Melanocallis caryaefoliae (Davis), can seriously damage pecan foliage, Carya illioensis (Wang.) K. Koch THE
(Tedders 1978, Dutcher 1985). In Georgia, earlyseason infestations of M. pecanis occur between budbreak and fruit enlargement (April-June), low midseason infestations occur during fruit enlargement to shell hardening (July-late August), and severe late-season infestations occur from shell hardening to harvest (late August-November). Populations of M. caryaefoliae can occur from budbreak to harvest, and severe infestations usually develop during midsummer (Dutcher 1985). Temperature may affect the aphid itself directly through its effects on development, survival, and water loss, or indirectly through its effect on aphid feeding sites (i.e., leaves). A number of studies have been conducted on the effects of constant temperatures on development and survival of M. pecanis and M. caryaefoliae (Tedders 1978, Flores-Flores 1981, Edelson 1982, Reilly & Tedders 1990, Tedders et al. 1992). There has been no detailed study on the effect of temporary exposure of M. pecanis and M. caryaefoliae to a wide range of temperatures including extreme hot and cold temperatures, although Tedders et al. (1992) reported the effect of a short 0046-225XJ93/0810-0817$02.00/0
© 1993 Entomological
caryaefoliae,
pecan
exposure to 40°C on first instars of M. pecanis and M. caryaefoliae. In pecan-growing areas of the United States, maximum temperature of 37°C or higher can occur for several hours each day during late July and early August, and this can occur on several consecutive days. Low temperatures between 4 and 8°C can also occur during early morning in late August through November and can last for 2-4 h. The purpose of our research was to examine M. pecanis and M. caryaefoliae in all available life stages for their ability to survive various constant temperatures (O-40°C) for a short time period. The trend of air temperatures within a pecan tree was recorded to determine the extent of temperature fluctuations and provide insight into how temperature might influence aphids at different parts of the tree. Materials and Methods Laboratory experiments were conducted in November 1991 and January 1992. Stock colonies of M. pecanis and M. caryaefoliae were established at least 1 rna before initiation of the experiment. Colonies were started from aphids on field-grown pecan trees. Aphids were maintained on pecan seedlings in growth cabinets in a rearing room at 23°C with 63% RH and a photoperiod of 16:8 (L:D) h.
Society of America
August 1993
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ON PECAN APHIDS
811
rAl 5~
T.m••"tu" ••••• \ under a roof shaped wooden piece
Fig. 1. Temperature probes (thermocouple sensors) used for field temperature monitoring on the west (W) and the northwest (NW) sites of a pecan tree. Location of the probe, its height from the ground, and distance from the trunk were as follows: probe 1 (W, 3.8 m, 10.4 m), probe 2 (W, 3.5,11.3), probe 3 (W, 2.8,12.5), probe 4 (NW, 2.5,8.5), probe 5 (W, 2.0, 11.0), probe 6 (W, 1.6, 12.8), and probe 7 (NW, 1.4, 0.05).
We determined the effect of high- and lowtemperature regimes, each with four levels, on nymph and adult stages of M. pecanis and M. caryaefoliae held on pecan foliage. Hightemperature levels were 30, 34, 37, and 40 ± 0.5°C. Low levels were 0, 6, 12, and 15 ± 0.5°C. Growth chambers with continuous fluorescent lights (Percival Manufacturing, Boone, IA) were set at the desired temperature at least 24 h before conducting the experiment. Relative humidity was not measured or controlled; however chamber humidity was maintained at a high level by
firmness) of the leaf sections during the 5-h experiments, we replaced old leaf sections with freshly harvested mature leaves every 2 h. Aphids in each dish were examined under the microscope to verify their survival before placing all dishes in the appropriate growth chambers. Cumulative numbers of surviving aphids in response to each temperature were recorded hourly for 5 h. An aphid was considered dead when it was lying motionless (sometimes legs were extended irregularly), its body was dried or discolored, and it gave no response to touch by a
filling the condensate pan with distilled water.
brush. When an aphid's movement was very
Aphid-infested pecan seedlings were removed from the rearing room and placed in the laboratory for 10 min before initiation of the experiments. Aphids were classified as winged adults (unknown age), large nymphs (third and fourth instars), or young nymphs (first and second instars). Ten aphids per stage per species were selected at random from colonies on seedlings and transferred with a fine brush to leaf sections (2 by 2 cm2) in 63-mm-diameter covered petri dishes. Leaf sections taken from expanded, mature leaves of field-grown pecan trees were washed for 1 min with distilled water, blotted on tissue papers to remove excess water from both leaf surfaces, and then placed lower surface down in the dishes. In an attempt to overcome the physiological changes (color, shape, and
slow and it was unable to right itself when lying on its back (sometimes legs were moving), it was called moribund but counted as alive. Air temperature fluctuations within a pecan tree ("=25 m diameter) were measured with thermocouple sensors or temperature probes. Six probes were hung by wire or tied to selected branches at different heights on the west and northwest sides of the tree at various distances from the tree trunk and pecan foliage (Fig. 1). The seventh probe was placed 5 cm from the bark surface of the trunk. A roof-shaped wooden piece (20 by 30 em) was placed 2-3 cm above each probe to reduce direct sunlight exposure on the probes. Thermocouple wires were connected to a remote automated information network (RAIN, Electronically Monitored Ecosystems,
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Berkeley, CAl for collecting hourly readings of temperatures each day between 2 and 27 July 1992. Statistical Analysis. Data for each aphid species and temperature regime were analyzed as split plot with time as repeated measure using the analysis of variance (ANOV A) (SAS Institute 1985), with temperature and stage as the main plots. Temperatures were not replicated because of time and availability of aphids; therefore, error terms for temperatures can be computed but cannot be used to compare temperatures. Time was used as a subplot with the replication * time as the error term for time within each temperature. Twelve replicates were done per stage per species and placed in a completely randomized design within the growth chamber. Small nymphs and adults of M. caryaefoliae and adults of M. pecanis were not available at the time of exposing aphids to 15 or 34°C; therefore, they were tested separately at a later time: aphids were placed in the same preset growth chambers and provided leaves from greenhouse-grown seedlings. Mean numbers of surviving aphids were separated using Fisher's protected LSD test (P < 0.05). The general linear model (GLM) (SAS Institute 1985) was used to determine the linear
effects as well as interactions for M. pecanis and M. caryaefoliae (Table 1). Life stages responded differently when exposed to different temperatures, as indicated by the highly significant (P < 0.05) Tm x St interaction. The St x Ti interaction was highly significant (P < 0.01), indicating that stages responded differently over time. Temperatures affected (P < 0.05) aphid survival over time, as indicated by the Tm x Ti interaction. The mean number of surviving aphids exposed to high-temperature regime decreased over time (Table 2), and their response curves contained highly significant (P < 0.01) linear components when averaged over the stage main effect. Little or no mortality was observed when aphids were exposed for 1 h to 30, 34, or 37°C, but mean number of surviving aphids declined progressively at 40°C, with 37 and 25% mortality recorded for M. pecan is and M. caryaefoliae, respectively. Aphids exposed to 30 and 34°C exhibited similar survival trends over time when averaged over other effects, but a higher mortality rate over time was seen starting at 37°C. After 5 h of aphid exposure to temperatures, low mortality was observed at 30 and 34°C, but the survival of M. pecanis and M. caryaefoliae at 37°C
and quadratic significance of the trend of time.
decreased,
The regression values for time were converted to deviations from the mean time (value of 3 h). Data from both aphid species were combined, within a given temperature regime, and the interactions of species main effect with temperature level, aphid stage, and time were presented. The sums of squares was partitioned into individual degrees of freedom to determine the significance of the main effects and interactions.
tively. Temperatures of 40°C were extremely detrimental, with 91 and 84% mortality for M. pecanis and M. caryaefoliae, respectively. Aphid survival decreased over time for all life stages (Table 2); however, large nymphs and adults of M. pecanis responded similarly over time when averaged over temperature levels and their responses were different (P < 0.05) from those of small nymphs. Stages of M. caryaefoliae differed (P < 0.05) in their responses when averaged over all temperature levels used. Aphids exposed to the low-temperature regime followed survival trends similar to those exposed to the high-temperature regime. The main effects of temperature, stage, and time were highly significant (P < 0.01), as were all possible first- and second-order interactions (Table 3). The mean number of surviving aphids decreased over time (Table 4), and their response curves contained highly significant (P < 0.01) linear components when averaged over the stage main effect. After 1 h of exposure little mortality was detected at all temperatures for both species. Higher mortality (2:15%) was observed after 2 h of exposure to O°C. After 5 h, 14 and 23% mortality were recorded for M. pecanis exposed to 15 and 12°C, respectively, and 20 and 31% mortality were recorded for M. caryaefoliae at the respective temperatures. Higher mortalities were recorded at 6°C, with 36 and 42% for M. pecanis and M. caryaefoliae, respectively. Freezing temperature (O°C) had a pronounced effect on aphid survival, with 81 and 90% mortality for M. pecanis and M. caryaefoliae, respectively.
Results Hourly observations of M. pecanis and M. caryaefoliae in dishes outside the growth chambers indicated that aphids showed a sharp decline in movement over time at 37°C compared with those exposed to 30 or 34°C. At extreme high temperatures (37 and 40°C), nymphs were motionless, with a body dried or discolored; wings of adults were shrunken and some were attached to the petri dish. Most surviving aphids in all temperature treatments continued to feed on the leaf section provided. At extreme low temperatures (6 and O°C), aphids were motionless or moved slowly but were more active when touched by a brush compared with those exposed to extreme high temperatures. Separate-Species Analysis. When aphid species were analyzed separately within a temperature regime, significant differences among the number of surviving aphids were detected. Aphids exposed to high temperature levels revealed highly significant (P < 0.01, AN OVA) temperature (Tm), stage (St), and time (Ti) main
with 62 and 49% mortality, respec-
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ON PECAN APHIDS
Table 1. Analysis of variance of mean number of M. pecani. and M. caryaefoliae surviving after exposure to high-temperature regime with a split-plot analysis using temperature and stage as the main plots and time as subplot Source of variation
df
Temperature (Tm) Stage (St) Tm x St Error a Time (Ti) Tm x Ti Error b St x Ti Tm x St x Ti Error c Total
3 2 6 132 4 12 220 8 24 308 719
Asterisk indicates
significance
M. pecanis
M. caryaefoliae
ANOVA SS
F value
ANOVA SS
F value
4,700.3 79.8 69.9 119.0 899.4 719.7 100.8 12.9 66.8 31.6 6,800.2
15,276.4' 44.3* 12.9*
3,377.0 124.9 134.4 126.5 623.9 630.1 100.6 14.9 48.9 22.6 5,184.1
99,999.9* 65.2* 23.4*
719.7* 584.8* 15.7* 27.1*
at the 1% level. Error a = replication
Aphid survival decreased over time in all life stages (Table 4); however, stages of M. pecanis differed (P < 0.05) in their responses when averaged over all temperature levels used. Large nymphs and adults of M. caryaefoliae responded similarly over time when averaged over temperature levels and their responses were different (P < 0.05) from those of small nymphs. Species-Combined Analysis. An analysis of the species (Sp) main effect, within a temperature regime, and its first-order interactions with temperature, stage, and time indicated that main effects were highly significant (P < 0.01) between species (Table 5). Also, the overall Tm x Sp interaction was highly significant (P < 0.01) under high-temperature regime. This interaction was not significant under the low-temperature regime, indicating similar response curves for
341.0* 114.8* 254.0* 277.8*
(Tm x St) and error b = replication
x Ti (Tm).
both species when averaged over temperature and stage main effects. The Sp >< St and Tm x Sp x St were only significant (P < 0.05) under the low-temperature regime, indicating that the stages of both aphid species responded similarly over other main effects and when exposed to different temperature levels. Significant differences between M. pecanis and M. caryaefoliae were found in the number of surviving aphids when averaged over all main effects (Table 6). Overall, M. caryaefoliae tolerated high temperatures better (P < 0.05) than M. pecanis, but at the low temperatures, M. pecanis was more tolerant (P < 0.05). Field Temperature Monitoring. Mean daytime temperatures within a pecan tree in July ranged from 27.7 to 31.4°C (Table 7). Cooler temperatures ranged from 23.1 to 26.7°C during the
Table 2. Main effects of temperature level, aphid stage, and time on mean number surviving after exposure to high-temperature regime
of M. pecani. and M. caryaefoliue
Mean no. surviving aphids Species
M. pecanis
M. caryaefoliae
Main effect
Time Temp (0C) 30 34 37 40 Aphid stage Small nymphs Large nymphs Winged adults Time Temp (0C) 30 34 37 40 Aphid stage Small nymphs Large nymphs Winged adults
Exposure time (h)
Significanceb
2
3
4
5
Meana (SEM)
9.3
8.5
7.8
6.6
6.3
7.7 (0.11)
**
**
10.0 10.0 9.9 7.2
10.0 9.9 9.1 5.0
9.9 9.8 8.6 3.0
9.8 9.7 5.7 1.4
9.4 9.6 5.1 1.1
9.8 9.8 7.7 3.6
(0.04) (0.03) (0.16) (0.19)
** .* .* *.
NS NS
9.0 9.4 9.5 9.6
8.0 9.0 8.6 8.8
7.2 8.3 7.9 8.4
6.1 6.9 6.9 7.4
5.9 6.4 6.6 7.0
7.3 8.0 7.9 8.2
(O.22)b (0.18)a (0.18)a (0.10)
•• •• ••
.*
10.0 10.0 10.0 8.3
10.0 10.0 9.5 5.6
10.0 10.0 8.9 4.7
9.9 9.8 7.3 2.7
9.9 9.7 6.3 2.0
10.0 9.9 8.4 4.6
9.2 9.7 9.8
8.1 9.1 9.0
7.8 8.7 8.6
6.8 8.0 7.5
6.4 7.6 6.9
(0.01) (0.02) (0.13) (0.20)
7.7 (0.20)c 8.7 (0.14)a 8.4 (0.16)b
Linear
NS
Quadratic
•• *.
•• NS NS NS
.*
••
.* .* **
.* NS *.
••
••
a For the stage main effect, means in the same column followed by the same letter are not significantly different (P > 0.05, Fisher LSD test). SEM for within a temperature level only and not to be used to compare temperatures. b NS, " and ** indicate nonsignificant or significant at the 5 and 1% levels, respectively.
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ENVIRONMENTAL
Vol. 22, no. 4
ENTOMOLOGY
Table 3. Analysis of variance of mean number of M. pecanu and M. caryaefoliae surviving after exposure low-temperature regime with a split-plot analysis using temperature and stage as the main plots and time as 8ubplot Source of variation
df
Temperature (Tm) Stage (St) Tm x St Error a Time (Ti) Tm x Ti Error b St X Ti Tm X St x Ti Error c Total
3 2 6 132 4 12 220 8 24 308 719
Significance
levels indicated:
M. pecanis
M. caryaefoliae
ANOVASS
F value
ANOVA SS
F value
1,097.2 16.2 34.5 73.3 1,040.1 550.8 71.2 7.2 40.2 63.3 2,994.0
1,780.4" 14.6" 10.4"
1,294.8 59.9 11.6 105.~ 1,531.7 625.1 1l0.6 40.7 21.6 67.9 3,868.8
1,957.9" 37.6" 2.4'
803.5" 141.8" 4.4" 8.2··
" P < 0.05; ", P < 0.01. Error a
nighttime period. Mean minimum temperatures for all probes during the day- or nighttime were uniform each week, with a slight increase in temperatures (1 ± O.S°C) during the 2nd wk of July. Mean weekly maximum day- or nighttime temperatures were recorded and had a range of 32.239.4°C or 29.4-33.9°C, respectively. Highest temperatures were recorded during the 2nd wk of July, but the trend of temperatures changed after a return to cooler conditions during the 3rd wk. Highest temperatures during the day were from probes located at the edge of the tree and exposed to more sunlight. Temperatures at the shady trunk tended to be reduced by >3°C compared with other temperatures obtained from other probes. Daily maximum temperatures during the nighttime were very uniform within each week of July.
=
to
replication
(Tm x St) and error b
761.4" 103.6" 23.1·· 4.1··
=
replication
x Ti (Tm).
Discussion For each aphid species there is a limited range of temperatures over which development and survival increase linearly. The relationship is curvilinear outside this range, and aphids are affected by extreme temperatures in which mortality rate increases (Chapman 1982). Thermal death-points (temperatures at which some aphids died after 1 h of exposure) of 38°C for Aulacorthum solani (Kaltenbach) and Acyrthosiphon pisum (Harris), 38.soC for Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer), and 41°C for Brevicoryne brassicae (L.) have been reported (Broadbent & Hollings 1951). Extreme high (37 and 40°C) and low temperatures (0 and 6°C) in this study had profound effects and caused mortality of both species tested.
Table 4. Main effects of temperature level, aphid stage, and time on mean number surviving after exposure to low-temperature regime
of M. pecani, and M. caryaefoliae
Mean no. surviving aphids Species
M. pecanis
M. caryaefoliae
Exposure time (h)
Main effect
Time Temp (0C) 15 12 6 0 Aphid stage Small nymphs Large nymphs Winged adults Time Temp (0C) 15 12 6 0 Aphid stage Small nymphs Large nymphs Winged adults
Significanceb
I
2
3
4
5
Mean" (SEM)
Linear
9.9
9.6
8.7
7.6
6.7
8.5 (0.08)
••
••
10.0 10.0 10.0 9.7
10.0 9.9 9.7 8.8
9.9 9.3 8.8 6.9
9.5 8.7 7.9 4.2
8.8 8.3 7.2 2.7
9.6 9.2 8.7 6.4
(0.05) (0.06) (0.10) (0.21)
" " ",.
NS
9.9 9.9 10.0 9.9
9.5 9.7 9.5 9.5
8.5 8.9 8.7 8.2
7.3 7.9 7.5 7.2
6.4 7.1 6.8 6.0
8.3 8.7 8.5 8.1
(0. 13)c (0.12)a (0.14)b (0.09)
•• ,.
10.0 10.0 10.0 9.7
10.0 9.8 9.5 8.5
9.5 8.8 8.3 6.3
9.2 8.4 7.6 3.5
8.2 7.5 6.5 1.6
9.4 8.9 8.4 5.9
(0.07) (0.08) (0.12) (0.24)
" "•• "
9.9 9.9 9.9
9.4 9.6 9.4
7.8 8.5 8.4
6.6 7.5 7.4
5.0 6.4 6.5
7.7 (0. 16)b 8.4 (0. 14)a 8.3 (0. 14)a
Quadratic
,. •
" "
.,
•• •• ,.
,.
"
NS
"
., ., .,
a For the stage main effect, means in the same column followed by the same letter are not significantly different (P LSD test). SEM for within a temperature level only and not to be used to compare temperatures. b NS, " " indicate nonsignificant or significant at the 5 and 1% levels, respectively.
" " " > 0.05,
Fisher
August 1993
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815
APHIDS
Table 5. Partial analysis of variance showing main effects and first-order interactions with aphid species effect from the species-combined (M. pecan~ and M. caryaefoliae) analysis after exposure to low- or high-temperature regime Temp regime Source of variation
df
Temperature (Tm) Species (Sp) Tm x Sp Stage (St) Sp x St Tm x Sp x St Time (Ti) Sp x Ti
High
3 I
3 2 2 6 4 4
Asterisk indicates significance
F value
ANOVA SS
F value
8,017.9 93.5 59.8 201.3 3.4 9.1 1,507.7 15.6
18,355.6" 100.6" 21.4" 108.3" 1.9 1.6 730.4" 26.8"
2,387.8 46.9 4.2 65.0 11.1 20.2 2,543.6 28.2
3,902.1" 69.5" 2.1 48.1" 8.2" 5.0" 981.9* 34.6*
at the 1% level.
Temperature is a major regulatory factor of pecan aphid abundance and appears to restrict aphid movement, rate of development, and survival (Tedders 1978, Tedders et al. 1992). Differences among pecan aphids in their outbreak times are affected by many factors. Forces that affect an equal population of each species may allow the survival of a higher proportion of that population having the highest rate of population increase. Differences in the population increase rate between M. pecanis and M. caryaefoliae have been reported, with a range of 0.258-0.353 and 0.200-0.264 progeny per female per day, respectively, at different times during the growing season (Kaakeh & Dutcher 1992). Large nymphs and alate adults in the study reported here tolerated a wide range of temperatures better than small nymphs. Tedders et al. (1992) stated that first instars of M. pecanis withstood 40°C for 2 h without mortality and with 65 and 100% mortality after 4 and 6 h, respectively. They also stated that first instars of M. caryaefoliae withstood 40°C for 8 h without 100% mortality and no aphids survived beyond 11 h. Similar tolerance of other aphid species to various temperatures has been reported (Harrison & Barlow 1973, Dixon 1985). Body temperature affects aphid survival. Aphid exposure to radiant heat might raise the body temperature of the aphid by 5-15°C above the air temperature and may cause death (Gunn 1942), espeCially for large, dark species such as Table 6. regime
Low
ANOVA SS
Tuberolachnus salignus (Gmelin) (Digby 1955). This may explain why most pecan aphids occur on the lower surface of leaves, where they are protected from direct exposure to sunshine. The color of pecan aphids may affect the amount of radiation absorbed and therefore influence body temperature. For example, M. caryaefoliae is black and may be few degrees hotter than the yellow aphid, M. pecanis, but there are no data to substantiate this assumption. The hot surface and internal temperatures of the plant may affect the feeding behavior of the aphids. Feeding aphids may cool themselves by evaporation or by resting on the cooler transpiring surface of the leaves (Broadbent & Hollings 1951). The temperature at which the death of pecan aphids occurs depends on the species, the duration of exposure, and interaction with other factors. Aphid response to temperature is not static, but varies according to the previous experience of the aphid. Chapman (1982) stated that the cause of death at lethal high temperatures (>40°C) for short-time exposure may be that the protein is denatured or the balance of metabolic processes is disturbed so that toxic products accumulate. At O°C, insects may die as a result of tissue freezing. The pattern of air temperature on or near leaf surfaces is unstable and may vary for each smallscale environment within a pecan tree. Greaves (1965) found that surface bark temperatures exposed to direct sunlight may reach 41°C when
Species main effect from the species-combined analysis after aphid exposure to low- or high-temperature
Mean no. surviving aphids Regime
High temperature Low temperature
a b
Species main effect
M. M. M. M.
pecanis caryaefoliae pecanis caryaefoliae
Exposure time (h)
Meana (SEM)
Significanceb Linear
Quadratic
1
2
3
4
5
9.3 9.6
8.5 8.8
7.8 8.4
6.6 7.4
6.3 7.0
7.7 (0.12)b 8.2 (O.lO)a
*
9.9 9.9
9.6 9.5
8.7 8.2
7.6 7.2
6.7 6.0
8.5 (0.08)a 8.1 (0.09)b
"*
For each temperature regime, means followed by the same letter are not significantly different (P Asterisk indicates significance at the 1% level.
> 0.05,
Fisher LSD test).
ENVIRONMENTALENTOMOLOGY
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Table 7. Air temperature fluctuations withina pecan tree at different heights and distances from the tree tMlnkand pecan foliage, July 1992 Thermocouple no.
Date 2-8
July (n =
84)
9-15
July (n =
84)
16-21
July (n =
72)
22-27
July (n =
72)
1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7
Temp (0C) Daytime(0700-1800 h) Nighttime(1900-0600 h) Mean(SD) Min. Mean(SD) Min. Max. Max. 29.0 29.3 28.8 28.7 29.0 29.4 29.5 30.9 31.1 30.7 30.6 30.9 31.4 31.3 27.7 28.0 27.7 27.7 27.8 28.0 28.2 29.3 29.5 29.1 29.1 29.9 29.6 29.7
(4.0) (3.8) (3.9) (3.5) (4.0) (4.7) (4.0) (4.0) (3.8) (4.0) (3.4) (4.0) (4.5) (3.9) (3.6) (3.3) (3.4) (2.9) (3.6) (3.9) (3.4) (3.9) (3.6) (3.7) (3.2) (4.4) (4.1) (3.7)
the shade air temperature is only 16°C. Air temperature measurements in the study reported here showed the variations in environment experienced by aphids within the pecan tree canopy. Both M. pecanis and M. caryaefoliae occur in mixed populations within the pecan foliage during May-June and from September to harvest. Very low midseason infestations occur during mid-July. The high air temperatures (>36°C) during mid-July (Table 7) may be reponsible for the absence or low infestation of aphids during that period on pecan foliage. Changes in light intensity around and within the pecan tree may also affect aphid feeding and survival. Direct comparison of results taken under natural light in the pecan orchard with those presented in this study under artificial light (which contains less ultraviolet than sunlight) is inappropriate. Results presented in this study may contribute to our understanding of the effect of temperatures (including the unfavorable extremes) on aphid survival. Temperature information may help to predict percentage aphid mortality, explain the outbreak of M. pecanis during hot midsummers and the usual outbreak of M. caryaefoliae during cooler springs and latesummers, and eventually help in pecan aphid management decisions when combined with weather predictions in pecan orchards.
21.1 21.7 21.1 21.7 21.1 20.6 21.7 22.8 23.3 22.8 23.3 22.8 22.2 23.3 21.1 21.7 21.1 21.7 21.1 21.1 21.7 21.7 22.2 21.7 22.2 21.7 21.7 22.2
34.4 35.0 34.4 33.9 35.6 37.8 35.0 36.1 36.1 36.1 35.0 36.7 38.3 36.7 32.8 32.8 32.2 32.8 33.3 35.0 33.3 35.0 34.4 33.3 33.3 39.4 36.1 34.4
24.7 25.1 24.5 24.9 24.6 24.5 25.2 26.2 26.6 26.0 26.5 26.2 25.7 26.7 23.3 23.8 23.4 23.7 23.4 23.1 23.8 24.7 25.2 24.5 25.1 24.2 24.4 25.2
(3.0) (3.0) (2.9) (2.9) (3.0) (3.1) (3.0) (2.4) (2.4) (2.3) (2.2) (2.4) (2.6) (2.4) (1.8) (1.8) (1.8) (1.6) (1.8) (1.9) (1.8) (2.4) (2.3) (2.3) (2.2) (2.0) (2.4) (2.3)
21.1 21.7 21.1 21.7 21.1 21.1 21.7 22.8 23.3 22.8 23.3 22.8 21.7 22.2 21.1 21.7 21.1 21.7 21.1 21.1 21.7 21.7 22.2 21.7 22.2 21.7 21.1 22.2
32.8 32.8 32.2 32.2 32.8 33.3 33.3 33.3 33.9 32.8 33.3 33.3 33.9 33.9 29.4 30.0 29.4 29.4 29.4 29.4 30.0 32.2 32.2 31.7 31.7 31.1 32.2 32.8
Acknowledgments We express appreciation to W. L. Tedders and B. W. Wood (USDA-ARS, Southeastern Fruit and Tree Nut Research Laboratory, Byron, GA) for their critical reviews of the manuscript. Thanks to Ben Mullinix for advice on statistical analysis of the data and to M. J. Townsend, D. R. Atkins, J. H. Gillman, and D. W. Cheek for technical assistance. This project was supported by Hatch funds allocated to project H-431 (S220) at the Coastal Plain Experiment Station of the University of Georgia College of Agricultural and Environmental Sciences. References
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