ESAposter05

1
Predicting Mole Cricket Oviposition and Hatch in
North Carolina
Peter T. Hertl, Rick L. Brandenburg, Ronald E.
Stinner and Cavell Brownie, North Carolina State
University, Raleigh, NC 27695-7613
ABSTRACT The timing of egg-hatch for both the
tawny mole cricket (Scapteriscus vicinus Scudder)
and southern mole cricket (S. borellii
Giglio-Tos) was quantified in southeastern North
Carolina. Nymphs were sampled weekly using an
irritant flush during the summers of 19931997 at
nine golf courses to compile a development data
base from a total of 20 site-years. Pronotal
length was used to assign the nymphs to size
classes, and counts were summarized on a m2
basis. The smallest size class was equated to
the first instar and counts were used to quantify
the timing of 25, 50, and 75 peak and cumulative
hatch. These data were further used to estimate
the timing of oviposition. On-site soil
degree-day accumulations and rainfall data from
local weather stations were examined to determine
their relationship to hatch timing. Soil
degree-days were correlated with the timing of
hatch however, calendar date quantified timing
better than degree-days. A relationship between
hatch and both soil degree-days and rainfall was
found. Differences in degree-day accumulations
and a soil moisture-related delay in oviposition
documented in previous greenhouse experiments are
believed responsible for differences observed in
annual development. Management implications of
the research are discussed.
RESULTS AND DISCUSSION Sampling Results. Most
sites were of mixed species composition, ranging
from 0.897.3 S. borellii. Sampling over all
years yielded a total of 14,753 nymphs (65.1 S.
vicinus and 34.9 S. borellii). When separated
into size classes, C1 nymphs represented 19.0 and
38.6 of the total nymphs collected for S.
vicinus and S. borellii, respectively. Peak
and Cumulative Hatch Date. Peak hatch data are
presented graphically in Figure 6. Mean dates
for cumulative hatch are reported in Table 1.
Results show significant differences in hatch
date among years for S. vicinus, but not for S.
borellii. Analysis of both peak and cumulative
hatch data result in similar hatch date estimates
for each species. S. vicinus hatch generally
takes place 15-16 d earlier than S. borellii.
Soil Degree-Days and Rainfall. Hatch dates for
both species were correlated with DD
accumulations, however, this may be due to
correlation between DD and date. Therefore,
quartile dates for cumulative hatch were compared
with soil DD at 10 d intervals prior to and
during the hatch period. The dates of 25 and 50
cumulative hatch for S. vicinus were
significantly correlated with soil DD at six and
four dates, respectively, with maximum negative
correlation at 30 May (Fig. 5). Hatch dates were
also compared to monthly rainfall for the
preceding April, May, and June (when the eggs are
laid). A significant correlation was found
between rainfall in June and all three hatch
dates for S. vicinus. Additionally, rainfall
during a 2 wk interval (27 May - 9 June) was
similarly correlated with date of hatch for S.
vicinus. Median hatch date for S. vicinus is 27
d after 30 May, so results for both DD and
rainfall suggest a relationship with oviposition
rather than hatch. No significant correlations
between DD or rainfall and S. borellii
cumulative hatch were found at any date. Models
Including Soil Degree-Days and Rainfall. Models
including soil DD at 30 May and monthly rainfall
(April, May, and June) were examined to determine
if both variables explained variation in date
hatch better than either variable alone.
Although both soil DD and rainfall were
correlated with S. vicinus hatch, including both
variables in models only explain 2.116.9 more
variation in date than either variable did alone.
The 30 May soil DD and June rainfall together
only explain 48.665.8 of the variation in date
of S. vicinus hatch, and these variables are not
significant in the models when both are
included. Estimates for the Date of Oviposition.
Estimates for the dates of cumulative oviposition
are reported in Table 1. These estimates were
made by subtracting both the duration of the egg
stage (19 and 21 d for S. vicinus and S.
borellii, respectively) and half the duration of
the first instar (7 and 11 d for S. vicinus and
S. borellii, respectively) from the mean dates of
hatch. Calculations using the earliest date for
C1 nymphs (3 June, for both species) suggest that
the date of first oviposition is 8 and 2 May for
S. vicinus and S. borellii, respectively.
However, temperature and moisture are likely to
significantly modify the timing of oviposition,
hatch, and duration of the first instar. Given
that some eggs probably hatched prior to the date
of first detection, and that development may
occur more slowly in the field, oviposition may
occur earlier than indicated. Using first
detection date, the longest egg incubation times
reported, and half the longest duration reported
for the first instar suggest that both species
may begin oviposition in mid-April.
Figure 1. Mole cricket pests of turfgrass in NC.
Figure 2. Mole cricket damage to bermudagrass.
INTRODUCTION Scapteriscus vicinus Scudder, the
tawny mole cricket and S. borellii Giglio-Tos,
the southern mole cricket (Fig. 1) cause serious
damage (Fig. 2) to turfgrass throughout the
southeastern US. Both species have a similar
1-yr life cycle in NC, but there are substantial
differences in the timing of flight, oviposition
and egg-hatch. Although flight activity begins
in March (Hertl et al. 2005), oviposition does
not take place until May or June. The eggs hatch
in June and July, however, the timing of hatch
can be affected by climatic conditions and varies
from year to year. Damage usually does not become
apparent until early August when the nymphs are
large and difficult to control (Short and Koehler
1979, Hertl and Brandenburg 2002).
Insecticides are currently the only management
strategy that provides acceptable control,
however, treatments are often ineffective due to
improper timing (Brandenburg and Williams 1993).
Applications are usually most successful when the
nymphs are small, and only provide acceptable
control if the residual effect lasts until the
eggs have hatched. However, many of the more
popular insecticides only have a limited period
of residual activity and are ineffective against
larger nymphs. Therefore, only a narrow window
of opportunity exists to implement control.
The objective of this research was to
quantify mole cricket development in southeastern
NC and to develop a phenological model for
egg-hatch to facilitate management. Because both
oviposition and hatch can not be directly
observed, we used the presence of the smallest
nymphs as an indicator of egg-hatch.
Figure 4. Hatch quantified using nymph counts.
Figure 3. Nymph sampling with a soap solution.
MATERIALS AND METHODS Nymph Sampling. Nine
coastal golf courses were sampled during the five
year study (1993-1997). Sampling was conducted
by applying 16 liters of a 0.4 aqueous solution
of dishwashing soap (Lemon Fresh Joy ) to a 1.0
m2 area of turf within areas showing recent mole
cricket damage (Fig. 3). The solution acts as an
irritant causing mole cricket nymphs to come to
the soil surface (Short and Koehler
1979). Processing of Specimens. The number,
species, and mid-line pronotal length of all
field-collected mole crickets were determined in
the laboratory. Variability in both size and the
number of instars makes it impossible to
accurately assign field-collected nymphs to a
specific instar (Hudson 1987, Braman 1993).
Therefore, the pronotal length ranges presented
by Matheny and Stackhouse (1980) were used to
categorize nymphs into size classes. Environmenta
l Data Rainfall data from local weather stations
were provided by the State Climate Office at N C
State University. Biophenometers were installed
at four locations and programmed to accumulate
soil degree-days (DD) within the range of
10430C. Data Analysis. All estimates of dates
and DD, and all tests of equality, correlation,
and analysis of variance were performed using SAS
software (SAS Institute, 2000). Nymph counts for
each size class were quantified as the mean
number of nymphs per m2 for each species, site,
and date. Season-long class counts of less than
15 nymphs were excluded from further analysis.
The date of the highest mean count for each size
class was identified as the peak date of
abundance. Date estimates for the quartiles (25,
50, and 75) of peak and cumulative abundance for
the smallest size class (C1) were also determined
and used as estimates for peak and cumulative
egg-hatch. The dates of peak and cumulative
hatch for each species were analyzed separately.
Date estimates for cumulative hatch were compared
to cumulative soil degree-day estimates for
corresponding dates, an independent set of
degree-day accumulations at 12 dates representing
10 d intervals (10 April - 29 July), and monthly
rainfall accumulations. Correlations between
degree days, rainfall, and hatch were
investigated further using models including
various combinations of both variables.
CONCLUSION Hatch and oviposition were
quantified by date and soil degree-days for both
species, and represent the first such estimates
for this region. Our results indicate that the
timing of egg-hatch is better quantified by date
than soil degree-days. Date estimates for peak
and cumulative hatch closely agree and provide
useful guidelines for timing sampling and
control. Information on degree-day accumulation
and rainfall can be used to adjust these dates
from year to year, and species composition must
also be taken into account. Although soil
degree-days and rainfall were both correlated
with timing, and explain some portion of the
variability in hatch, neither fully explain
differences in hatch date among years.
Correlation between these variables further
complicates analysis, however, the unknown
physiological and behavioral responses to
temperature and moisture probably have a greater
effect. Quantifying the exact nature of the
relationship will require information on soil
moisture levels at the time of oviposition, and
experiments to determine the effects of
temperature and moisture on egg incubation time,
hatch, and nymph development.
LITERATURE CITED Braman, S. K. 1993. Progeny
production, number of instars, and duration of
development of tawny and southern mole crickets
(Orthoptera Gryllotalpidae). J. Entomol. Sci.
28(4)327330. Brandenburg, R. L. and C. B.
Williams. 1993. A complete guide to mole
cricket management in North Carolina. NC Coop.
Ext. Ser. ENT/ort - 101 8 pp. Hertl, P. T., R. L.
Brandenburg and M. E. Barbercheck. 2001. Effect
of soil moisture on ovipositional behavior in the
southern mole cricket (Orthoptera
Gryllotalpidae). Environ. Entomol. 30(3)
466473. Hertl, P. T. and R. L. Brandenburg.
2002. Effect of soil moisture and time of year
on mole cricket (Orthoptera Gryllotalpidae)
surface tunneling. Environ. Entomol. 31(3)
476481. Hertl, P. T., R. L. Brandenburg, and C.
Bruce Williams III. 2005. Flight activity of
Scapteriscus vicinus and S. borellii (Orthoptera
Gryllotalpidae) in southeastern North Carolina.
Int. Turf. Soc. Res. J. 10 723733. Hudson, W.
G. 1987. Variability in development of
Scapteriscus acletus (Orthoptera
Gryllotalpidae). Fla. Entomol. 70(3)
403404. Matheny, E. L. and B. Stackhouse. 1980.
Seasonal occurrence and life cycles data for S.
acletus and S. vicinus, field-collected in
Gainesville, Florida. Ann. Rep. No. 2, Mole
Cricket Research 7980 1924. SAS Institute.
2000. SAS/STAT users guide, version 8e. SAS
Institute, Cary, NC. Short, D. E. and P. G.
Koehler. 1979. A sampling technique for mole
crickets and other pests in turfgrass and
pasture. Fla. Entomol. 62(3)282283.
Figure 5. Trend in correlation between
cumulative hatch of S. vicinus and soil
degree-days at twelve dates.
Figure 6. Peak hatch profile for mole crickets
in NC.