Yellow Sugarcane Aphid: Insect Numbers and Feeding Damage to Bermudagrass andCentipedegrassAuthor(s): B. R. Wiseman, J. L. Skinner and R. E. LynchSource: The Florida Entomologist, Vol. 65, No. 4 (Dec., 1982), pp. 577-578Published by: Florida Entomological SocietyStable URL: http://www.jstor.org/stable/3494693 .

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Scientific Notes 577 female. Only a female emergee would definitely point to which of the 2 eggs survived; it would be the one that was laid by the mated female. In group A, 10 host cocoons were parasitized first by mated females. The second ovipositions were by virgin females and took place at intervals between 1 and 7 days. In group B, 14 cocoons were parasitized first by virgin females. The second ovipositions were by mated females and took place after intervals of 0-6 days.

From each cocoon of both groups, only one adult wasp emerged. However, females were secured only in 2 cases of groups A (superparasitism interval of 1 and 3 days) and 2 cases of group B (superparasitism interval of 0 and 3 days). Therefore in superparasitism of 0-3 days interval, the one egg that continued development could be either the first or the second one laid. A fe- male emerging in group B has the additional significance of serving as solid evidence of superparasitism, indicating that a second egg was actually laid. Therefore, future egg tagging tests involving superparasitism should follow the group B design, i.e. the second ovipositions accomplished by mated fe- males. (This investigation received support from the Academic Grant Fund of Loyola University.) -K. T. KHALAF, Loyola University, New Orleans, LA 70118, U.S.A.

YELLOW SUGARCANE APHID: INSECT NUMBERS AND FEEDING DAMAGE TO BERMUDAGRASS AND CENTIPEDEGRASS-The yel- low sugarcane aphid, Sipha flava (Forbes), has recently been recognized as a potentially serious pest of sorghum, Sorghum bicolor (L.) Moench (Starks and Mirkes. 1979, J. Econ. Ent. 72: 486-8.). In attempts to maintain a cul- ture of this insect in the greenhouse for eventual sorghum germplasm evaluation, we found that the aphids heavily infested nearby flats of both bermudagrass, Cynodon dactylon (L.) Pers., and centipedegrass, Eremochola ophiuroides (Munro) Hack. Skinner and Wiseman (1980 Sorg. Newsl. 23: 90-1.) reported that the yellow sugarcane aphid could be maintained on centipedegrass and then transferred to bermudagrass or sorghum for rapid buildup of the culture. We report here results of preliminary tests that evaluated the plant-insect interaction in Coastal bermudagrass and common centipedegrass.

The 1st test was designed as a 2-way choice as reported by Wiseman et al. (1982, J. Econ. Ent. 75: 245-7) to evaluate preference or nonpreference of the aphid obtained from a susceptible sorghum for common centipedegrass and Coastal bermudagrass. Two excised leaf sections (ca. 5 cm) of each grass were arranged in a 25-cm plastic dish in a randomized complete block design for each of 10 replications in each of 3 separate tests. Twenty aphids/ replicate were introduced into the center of each dish and the dishes were immediately placed in an incubator (26.7 ?2?C, 80 ?2% RH) under total darkness. The number of aphids on the leaf sections was counted after 16 h.

In a greenhouse test, 2 late-instar yellow sugarcane aphids were caged on a leaf blade of a live plant of bermudagrass and centipedegrass for each of 10 replications for each of 2 separate tests. Small rectangular plastic cages (6 cm x 2 cm x 3 cm) similar to those used in alfalfa plant resistance studies were used (Thomas et al. 1966. J. Econ. Ent. 59: 444-8). At the end of 10 days, the aphids on each leaf blade were counted and the damage to the

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578 Florida Entomologist 65 (4) December, 1982

leaves was visually rated by a rating scale of 0-9 where 0 = no damage and 9= entire leaf dark brown or dead.

The 3rd test was conducted in the laboratory with excised leaf sections of bermudagrass and centipedegrass placed in vials of water. Three late- instar yellow sugarcane aphids were introduced per leaf. The experiment was designed as a randomized complete block with 15 replications. At the end of the 5-day test period, aphid numbers and damage ratings were as- sessed. Analysis of variance of the data was calculated for each test and a combined analysis was calculated when applicable. Means for each test and combined means were separated by Duncan's multiple range test.

Results of the tests indicate that bermudagrass is significantly (P 0.05) preferred over centipedegrass by the aphids (Test 1, 4.9 vs 1.1; Test 2, 10.9 vs 2.8; Test 3, 13.8 vs 2.3, and mean of 3 tests, 9.9 vs 2.1, respec- tively). When late instar aphids were confined on a leaf blade of living plants, significantly more aphids were produced on the bermudagrass (Test 1, 14.8 vs 7.2; Test 2, 16.7 vs 8.8, and mean of both tests, 15.8 vs 8.0, re- spectively) than on centipedegrass. Leaf damage ratings were also signifi- cantly higher on bermudagrass than on centipedegrass (8.0 vs 3.0). How- ever, when the aphids were confined on excised leaves, significantly more aphids were produced on the centipedegrass than on bermudagrass (9.1 vs 4.2), probably because the aphids quickly killed the bermudagrass leaf sec- tions, and the aphids were unable to survive without food. It appears from these data that centipedegrass in the presence of bermudagrass is non- preferred and that a portion of this resistance may be due to antibiosis, as indicated by fewer numbers of aphids being produced on the centipedegrass. A greater amount of tolerance is present in centipedegrass, as indicated by more aphids produced on the excised leaves of centipedegrass, while very little damage occurred.-B. R. WISEMAN, J. L. SKINNER, AND R. E. LYNCH,

Southern Grain Insects Research Laboratory, ARS, USDA, Tifton, GA 31793 USA.

DIURNAL VARIATION IN SWEEP NET ESTIMATES OF GEOCORIAS PUNCTIPES (SAY) (HEMIPTERA: LYGAEIDAE) DENSITY IN COTTON-Sweep net estimates of insect density are influenced by several factors and may vary depending on the time of day samples are collected (Southwood. 1978. Ecological Methods. Methuen, London. 524 p.). Sweep net collections of Geocoris punctipes (Say) for predation studies appeared to yield more insects in the afternoon than at other times during the day. To verify this apparent trend, a study was conducted to determine varia- tions in sweep net estimates of G. punctipes density in cotton with time of day.

A field of cotton, Gossypium hirsutum (L.) cv. 'Stoneville 213', planted in four-row blocks (33m long) in Oktibbeha Co., Mississippi, was used for study. Plants were in early square stage and averaged 54?7 cm in height. Within the field, 6 replications of 50 sweeps each were obtained at 2-h inter- vals from 0700-1700 h (CST) on each of 6 days between 15 August and 5 September 1979. Mean minimum and maximum ambient temperatures dur- ing the 0700-1700 h sampling period were 21.6+2.10 and 31.842.00C. Plants

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