May 25, 1982 - Availability of fruit in the seven edible age classes as a proportion of total edible fruit. Deltapine 16, 1977/1978 season, Lockyer Valley, Qld., ...
Protection Ecology, 4 (1982) 371- 380 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
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RESPONSES OF DELTAPINE 16 COTTON GOSSYPIUM HIRSUTUM L. TO SIMULATED ATTACKS BY KNOWN POPULATIONS OF HELIOTHIS LARVAE (LEPIDOPTERA: NOCTUIDAE) IN A FIELD EXPERIMENT IN QUEENSLAND, AUSTRALIA^ L.T. WILSON and A.L. BISHOP* Department of Entomology, University of California, Dauis, C A 9561 6 ( U . S . A . ) *Horticultural Research Station, Narara, N.S. W. (Australia)
?This study was conducted in conjunction with the Integrated Pest Management Unit (I.P.M.U.), University of Queensland, Brisbanc, Qld. 4067, Australia (Accepted 25 May 1982)
ABSTRACT Wilson, L.T. and Bishop, A.L., 1982. Responses of Deltapine 16 cotton Gossypium hirsutum L. t o simulated attacks by known populations of Heliothis larvae (Lepidoptera: Noctuidae) in a field experiment in Queensland, Australia. Prot. Ecol., 4 : 371- 380. The applicability of simulated damage for estimating pest economic thresholds depends on the degree t o which real damage is mimicked. Results from this experiment indicate that the economic importance of Heliothis larval damage depends not only on the intensity of damage during a particular stage of plant growth but also on subsequent damage. Early season damage may enhance yield with only a delay in crop maturation, while late season damage can cause a yield reduction. In general, earlier and more intense the damage t o fruiting structures (squares (flower buds), flowers, and bolls), higher the yield and greater the delay in crop maturation; while later and more intense the damage, lower the yield and less the effect on crop maturation. The compensatory effect of early season damage can, however, be negated by later damage and a yield reduction may likely result.
INTRODUCTION
Cotton’s ability to compensate for damage and the degree to which compensation occurs depends on the type of damage, its intensity, duration and timing. Damage to cotton due to arthropod feeding usually occurs to leaves or fruit (squares (flower buds), flowers, bolls). Studies where leaves or fruit are removed have shown that yield reduction is most severe when the damage occurs during the period of boll maturation (Singh and Choudri, 1937; Dunnam et al., 1943; McKinlay and Geering, 1957; Passlow and Trudgian, 1960; Evenson, 1969; Rahman, 1977). Some of these results have also shown that cotton can overcompensate (increased yield) for high levels of fruit damage (up to 100%)occurring prior to flowering.
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Simulated fruit damage (disbudding) studies until recently had in common removal of a fixed percentage or number of squares and/or flowers and bolls for a variable duration. Useful information on the effects of altering the metabolic supply-demand ratios on plant growth, development, and yield has been obtained; however, these studies mimic little the feeding behaviour of a population of fruit feeders. Recent attempts have been made to develop models describing the fruit attack pattern of Heliothis spp. (Lepidoptera: Noctuidae) on cotton. Brown et al. (1977) used their Heliothis model t o predict the effect of computer simulated damage on yield. Blood and Wilson (1978) using a more detailed Heliothis fruit predation model (see Wilson and Gutierrez, 1980) simulated damage by cohorts of larvae at different periods of crop growth to estimate the effect on yield. The present study reports on a field study which used computer simulated results t o estimate the numbers of fruit in different age classes t o be removed to mimic damage occurring during Heliothis larval development at various intensities and at different stages of crop growth. METHODS AND MATERIALS
Damage to fruiting structures by Heliothis larvae was estimated taking into account larval density, feeding rates, availability of fruiting structures in different age classes, the relative probability of larvae in each instar encountering fruit in each age class (within-plant stratification differences), and the relative preference for these fruit (Blood and Wilson, 1978; Wilson and Gutierrez, 1980; Wilson and Waite, 1982). The numbers and classes of fruit attacked change both as the larvae age and as the plants through different stages of growth (Quaintance and Brues, 1905; Kincade et al., 1967; Tanskiy, 1969; McIntyre, 1972; Baldwin et al., 1974; Stanley, 1978; Hassan, 1980; Wilson and Gutierrez, 1980; Wilson and Waite, 1982). Because the availability of fruit of different ages changes as the plants develop (more bolls are available later in the season), the number of fruit in the seven edib!e age classes (three square sizes, flowers and three boll sizes) (see Table I) was estimated from five randomly chosen plants for each treatment 3 days prior to initiation of damage during the three crop stages. Coefficients of relative preference and stratification and feeding rates derived by Wilson and Gutierrez (1980) were used in equations (1)and (2) t o predict fruit damage.
Pij = AiSijCij (f AiSijCij)
-' ,
for each jth instar larval age class
where f i j = the proportion of attacks by jth instar larvae against the ith fruit age class (0 < P < 1);Ai = the proportion of total fruit in the fruit population belonging to the ith age class (0 < A < l),i = 1, 2, 3, . . ., 7 ;Sij = the relative preference ( 0 < S < 1)that jth instar larvae have for the ith fruit age class; Cij = the relative within plant stratification coefficient (0 < C < 1)
373 TABLE I Availability of fruit in the seven edible age classes as a proportion of total edible fruit. Deltapine 1 6 , 1977/1978 season, Lockyer Valley, Qld., Australia
Crop stage Early squaring (16 Dec.) Peak squaringearly boll ( 6 Jan.) Boll maturation (10 Feb.)
Fruit category *
ss
MS
LS
0.59
0.26
0.15
0.52
0.22
0.36
0.13
F
SB
0.21
0.01
0.04
0.19
0.02
0.06
MB
LB
0.05
0.20
*The SS, MS, LS and SB, MB, LB are small, medium and large squares and bolls respectively, and F is the flower stage. The sizes (length cm) are SS 0.05) affected by early season damage (Table VI). TABLE VI Comparison of individual treatment yields (bales/ha) means of three replicates. C = control (no damage), L = low damage, H = high damage. 1977/1978 season, Lockyer Valley, Qld., Australia Treatment*
Yield**
Treatment
Yield
Treatment
Yield
ccc CCL CCH
6.32 6.06 5.72
LCC LCL LCH
7.62 6.55 5.80
HC C HCL HCH
6.80 6.91 6.09
CLC CLL CLH
6.19 6.33 6.39
LLC LLL LLH
6.35 6.60 5.44
HLC HLL HLH
5.99 6.08 6.36
CHC CHL CHH
6.14 7.07 6.41
LHC LHL LHH
7.00 5.23 5.17
HHC HH L HHH
6.82 6.48 5.95
*The three symbols represent the damage level occurring during the early squaring, peak squaring-early boll and boll maturation periods respectively. **Bale = 217.9 kg; ca. 0.35 g lint/g seed cotton.
Mid season damage Damage during this period occurs predominantly t o squares and, except when interacting with damage occurring at other stages of crop growth (see later sections and Table IV), such damage,(at the intensities examined) appears only t o affect the proportion of open bolls with increased damage advancing maturity slightly. This is probably largely due to these fruit having a very low probability of surviving due to the rapidly increasing nutrient demand placed upon the plant population by the developing bolls (Gutierrez, 1975).
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Late season damage Increased damage late season significantly decreased yield and appears to decrease boll numbers and boll weight. The crop has little time to compensate for damage during this period and a decrease in number of bolls and yield was expected. The decrease in boll weight may imply that a greater proportion of bolls damaged during this period were larger bolls (not older). Crop maturity measured as the number and proportion of opened bolls was not significantly affected.
Interaction o f damage a t different crop stages The interaction of damage occurring at different stages of crop growth depends largely upon the stages at which damage occurs, the intensity of damage at these stages, and the parameters being measured (Table IV). The greatest effect appears t o occur with damage early season and mid season, or mild and late season. The early and mid season interaction had the same general effect for all parameters with the exception of seed cotton weight per boll which was not affected. Although the crop can tolerate a fairly high level of damage early season, as damage increases mid season there is a level at which the potential advantage (yield increase) of early season compensation is lost. The same general pattern also occurs when damage occurs early and late season or mid and late season, although the magnitude of the interactions can be expected to differ. The limited number and small size of the plots made it impossible to derive clear damage response curves; and in some cases a general relationship was not evident. This study indicates that the cotton crop can compensate for high levels of damage during the early and mid season stages of crop growth with the cost of such damage being a delay to crop maturity. Wilson et al. (1982) reported similar results from H . zea (Boddie) field damage experiments. Compared with a commonly used treatment threshold of 2 larvaelm-row (Adkisson et al., 1964), our levels of damage ranged from equal to nearly twice this level for the low level (L), and from 6.5 t o 11-times the high level (H) (Table 111). The cost of such damage is dependent on season length; and in short season areas, yields may be reduced by early frosts and harvests complicated by end of season rains (Evenson, 1969). Damage during the boll maturation stage, however, can result in a substantial reduction in yield (Table IV). The low and high damage treatments during this stage yielded 96.8 and 90% of the no damage (C) treatments (6.58 bales/ha). At a market price of $2 (U.S.)/kg of lint (217.9 kg per bale) and a cost of two sprays for control during this period ($40/ha) this equates t o a threshold of approximately 0.33 fourth instar or older larvaelm-row. This estimate of course depends on the current market value of cotton, the cost of treatment (pesticides + application) and the abundance of predators within a crop. The number of larvae and their age class breakdown reflects the popula-
379
tion pressures and the predator and climatic induced mortality in the area, where mortality is low due to lack of predators and mild weather, the numbers of fruit damaged by a cohort of larvae may be greater than that caused by the numbers used on this study. Older Larvae damage a far greater number of fruit, and although a lower number of first instar larvae may be present initially, lower mortality could result in a higher number of later larvae and more total damage. This points out the need for dynamic economic thresholds based on the mortality factors intrinsic t o an area. Likewise cotton cultivars may respond differently to damage due to the manner in which the larvae damage the crop (Wilson and Gutierrez, 1980) or a cultivar's ability to compensate for damage (Brown, 1965). The extreme difference between the damage inflicted upon a crop early or mid season and the resulting yield effect in comparison with that occurring late season reflects the need for thresholds based on the stage of crop development. Our method of fruit removal consisted of removing the complete fruit body and does not allow for any nutrient remobilization as undoubtedly happens with structures which are in the process of shedding due t o damage or normal physiological stress. This implies that our simulated damage may be an overestimate. At our current level of understanding of the cotton crop and its response to damage, this error is acceptable; however, it implies that more detailed plant damage studies are necessary for thresholds t o reach the fine tuning stage. ACKNOWLEDGEMENTS
We thank D. Morgan and B. Pyke for their assistance, the Integrated Pest Management Unit (I.P.M.U.) at the University of Queensland for providing transportation, and A. Brimblecombe for the generous use of his land. We also thank Drs. T.F. Leigh and D. Gonzalez for reviewing the manuscript and providing useful suggestions.
REFERENCES Adkisson, P.L., Hanna, R.L. and Bailey, C.F., 1964. Estimates of the numbers of H d i o t h i s larvae per acre in cotton and their relationship t o the fruitinh cycle and yield of the host. J. Econ. Entomol., 57: 657- 663. Baldwin, J.L., Walker, J.K., Cannaway, J.R. and Niles, G.A., 1974. Semi dwarf cottons and bollworm attack. J. Econ. Entomol., 67: 779-782. Blood, P.R.B. and Wilson, L.T., 1978. Field validation of a crop/pest management model. Simulation Modeling Techniques and Applications, Proc. SIMSIG-78, pp. 91- 94. Brown, J.K., 1965. Response of three strains of cotton t o flower removal. Emp. Cotton Grow. Rev., 4 2 : 279- 286. Brown, L.G., Jones, J.W., Hesketh, J.D., Hartsog, J.D., Whisler, F.D., McClendon, R.W., Harris, F.A., Parvin, O.W. and Pitre, H.N., 1977. The use of simulation t o predict cotton yield losses due t o insect damage. Proc. Beltwide Cotton Prod. Res. Con€., Atlanta, GA, January 1977. National Cotton Council, Memphis, TN, 258 pp.
380 Dunnam, E.W., Clark, J.C. and Calhoun, S.L., 1943. Effect of removal of squares on the yield of upland cotton. J. Econ. Entomol., 36: 896-900. Evenson, J.P., 1969. Effects of floral and terminal bud removal in the yield and structure of the cotton plant in the Ord Valley, North Western Australia. Cotton Grow. Rev., 46: 37-44. Gutierrez, A.P., Falcon, L.A., Loew, W., Leipzig, P.A. and Van den Bosch, R., 1975. An analysis of cotton production in California: A model for Acala cotton and the effects of defoliators on its yields. Environ. Entomol., 4 : 125-136. Hassan, S.T.S., 1980. Distribution of Heliothis armigera (Hiibner) and Heliothis punctigera Wallengren (Lepidoptera: Noctuidae) eggs and larvae, and insecticide spray droplets on cotton plants. Ph.D. Dissertation, Dep. of Entomology, University of Queensland, Brisbane, Qld., 127 pp. Kincade, R.T., Laster, M.L. and Brazzel, J.R., 1967. Damage t o cotton by the tobacco budworm. J. Econ. Entomol., 60: 1163-1164. McIntyre, R.C., 1972. Evaluation of various population densities of the bollworm, Heliothis zea (Boddie), on the growth characteristics of Deltapine-16 cotton. Ph.D. Dissertation, University of Arizona, Tucson, AZ, 1 5 0 pp. McKinlay, K.S. and Geering, Q.A., 1957. Studies of crop loss following insect attack on cotton in East Africa. Bull. Entomol. Res., 48: 833-849. Passlow, T . and Trudgian, K.G., 1960. Effects of fruits form removal on cotton yields in central Queensland. Queensl. J. Agric. SOC.,17: 311-320. Quaintance, A.C. and Brues, C.T., 1905. The cotton bollworm. U.S.Dep. Agric. Bur. Entomol. Bull., 50: 1-155. Rahman, M.A., 1977. Response to the cotton plant (Gossypium hirsutuni cv. Rex. S.L. Okra) to defoliation and disbudding. Ph.D. Dissertation, Dep. of Agric., University of Queensland, Brisbane, Qld., 261 pp. Singh, B.N. and Choudri, R.S., 1937. The role of deflowering in cotton production. Emp. Cotton Grow. Rev., 14: 126-133. Stanley, M.S., 1978. Competitive interactions between larvae of Heliothis armigera (Hiibner) and Heliothis punctigera Wallengren (Lepidoptera: Noctuidae). Ph.D. Dissertation. Australian National University, Canberra, A.C.T., 212 pp. Steele, R.G.D. and Torrie, J.H., 1960. Principles and Procedures of Statistics. McGrawHill Book Co., New York, 481 pp. Tanskiy, V.I., 1969. The harmfulness of the cotton bollworm. Heliothis obsoleta F. (Lepidoptera: Noctuidae) in Southern Tadyhikistan. Entomol. Rev., 48: 23-29. Wilson, L.T. and Gutierrez, A.P., 1980. Fruit predation submodel: Heliothis larval feeding upon cotton fruiting structures. Hilgardia, 48: 24-86. Wilson, L.T. and Room, P.M., 1982. The relative efficiency and reliability of three methods for sampling arthropods in Australian cotton fields. Aust. Entomol. SOC.,21: 175-181. Wilson, L.T. and Waite, G.K., 1982. Feeding pattern of Australian Heliothis on cotton. Environ. Entomol., 11: 297-300. Wilson, L.T., Gonzalez, D. and Leigh, T.F., 1982. Bollwaorm damage and yield of cotton infested at different time periods, J. Econ. Entomol., 75: 520-523.
