No description available.

No description available.

No description available.

Field studies of the blackmargined aphid, Monellia caryella (Fitch), were conducted on three cultivars, ‘Cheyenne’, ‘Kiowa’, and ‘Pawnee’, of pecan, Carya illinoinensis (Koch). Aphid density and natural enemy (lacewings, ladybird beetles, and spiders) densities were determined biweekly by direct inspection of 160 leaves per variety during the 2005 and 2006 growing seasons. Honeydew deposition was measured biweekly using water sensitive cards. Aphid phenologies were similar among cultivars; however, ‘Cheyenne’ supported higher densities of aphids than either ‘Kiowa’ or ‘Pawnee’. Honeydew production correlated positively with aphid density. Honeydew produced per aphid differed only between ‘Cheyenne’ and ‘Pawnee’ in 2006; natural enemies per aphid varied in significance during both seasons. Natural enemy densities increased during initial stages of outbreak on all cultivars in 2006. The asymptote reached on ‘Cheyenne’ had a lower natural enemy to aphid ratio than that on the other cultivars, indicating that the functional response of natural enemies to increased aphid densities was exhausted sooner on ‘Cheyenne than on other cultivars’. Honeydew appears to be an attractant for natural enemies and cost-benefit calculations were made to quantify the loss of photosynthates to aphids for each cultivar versus the gain in natural enemies that occurred. ‘Cheyenne’ was the least efficient of the three cultivars in the utilization of this defense mechanism. The energy drain per hectare attributable by adult aphid feeding was, 761,197 – 900,312kcal, 266,397 – 237,709kcal, and 138,790 – 134,223kcal for ‘Cheyenne’, ‘Kiowa’, and ‘Pawnee’, respectively. Calculated nut-loss equivalents were 14 – 16kg for ‘Cheyenne’, 4 – 5kg for ‘Kiowa’, and 2kg for ‘Pawnee’.

Field studies of the blackmargined aphid, Monellia caryella (Fitch), were conducted on three cultivars, 'Cheyenne', 'Kiowa', and 'Pawnee', of pecan, Carya illinoinensis (Koch). Aphid density and natural enemy (lacewings, ladybird beetles, and spiders) densities were determined biweekly by direct inspection of 160 leaves per variety during the 2005 and 2006 growing seasons. Honeydew deposition was measured biweekly using water sensitive cards. Aphid phenologies were similar among cultivars; however, 'Cheyenne' supported higher densities of aphids than either 'Kiowa' or 'Pawnee'. Honeydew production correlated positively with aphid density. Honeydew produced per aphid differed only between 'Cheyenne' and 'Pawnee' in 2006; natural enemies per aphid varied in significance during both seasons. Natural enemy densities increased during initial stages of outbreak on all cultivars in 2006. The asymptote reached on 'Cheyenne' had a lower natural enemy to aphid ratio than that on the other cultivars, indicating that the functional response of natural enemies to increased aphid densities was exhausted sooner on 'Cheyenne than on other cultivars'. Honeydew appears to be an attractant for natural enemies and cost-benefit calculations were made to quantify the loss of photosynthates to aphids for each cultivar versus the gain in natural enemies that occurred. 'Cheyenne' was the least efficient of the three cultivars in the utilization of this defense mechanism. The energy drain per hectare attributable by adult aphid feeding was, 761,197 - 900,312kcal, 266,397 - 237,709kcal, and 138,790 - 134,223kcal for 'Cheyenne' , 'Kiowa', and 'Pawnee', respectively. Calculated nut-loss equivalents were 14 - 16kg for 'Cheyenne', 4 - 5kg for 'Kiowa', and 2kg for 'Pawnee'.

Thesis (M.S.)--Ohio University, August, 2008. / Title from PDF t.p. Includes bibliographical references.

Thesis (MSc Natural and Agricultural Sciences)--University of Pretoria, 2007. / Includes bibliographical references. Summary in English.

Laboratory maintained Sitobion avenae of all developmental stages had a mean inherent supercooling ability below -20°C. Acclimation alone, or in conjunction with starvation had no significant effect on supercooling. Surface moisture on the aphid cuticle during cooling resulted in a significant loss in supercooling. Repeat coolings to temperatures markedly above the mean supercooling point resulted in increasing levels of mortality. Field collected ~ avenae showed a seasonal variation in supercooling with a higher mean supercooling point in the winter than in the remainder of the year. Field populations showed a dramatic decline in December when environmental temperatures were well above mean and individual supercooling points. It was concluded that the aphids were dying before they froze and that the supercooling point was not a reliable indicator of the lower lethal temperature. The development and reproduction of s.avenae in the field over winter were directly and positively related to temperature whilst mortality increased with decreasing temperature. The development of a multi-channel micro-bead thermistor unit allowed the study of a previously unrecorded thermal event (exotherm) during the cooling of aphids. The cause of the exotherm is unknown and warrants further investigation. Laboratory experiments on ~ avenae and the lupin aphid, Macrosiphum albifrons revealed that the adults of the two species had lower lethal temperatures (LT50) of approximately -7.5°C and -7.0°C respectively. Nymphs of ~. ayenae were significantly more cold hardy than adults in terms of LT50 values. Acclimation prior to experimentation significantly improved the cold hardiness (LT50) of s.avenae. It is concluded that in the case of s.avenae and other aphids supercooling points are ecologically irrelevant if aphids are already dead before they freeze. An experimental protocol is suggested for future experiments on insect cold hardiness.

The role of juvenile hormone (JH) in alate-apterous polymorphism was investigated in the green peach aphid, Myzus persicae. At higher concentrations (65 ppm), the juvenile hormone analogue (JHA), kinoprene, was immediately toxic to apteriform nymphs. At lower concentrations (10 ppm), the compound was non-toxic and exhibited no apparent morphological activity in apteriform stages. In contrast, 65 ppm kinoprene administered to alatiform nymphs had juvenilizing and apterizing effects. The extent of these effects depended upon when the kinoprene was applied. Fourth instar alatiforms were the least sensitive as kinoprene-treated nymphs developed into normal adults with reduced sclerotization and pigmentation. Kinoprene-treated third instars underwent a supernumerary moult before metamorphosing into adults with malformed wings. Sclerotization and pigmentation were also lacking in these insects. When first and second instar alatiformsiwere treated with kinoprene, they also underwent a supernumerary moult. The adults which emerged exhibited both larval and apterous characteristics. Wing development was almost totally inhibited; the cauda and genital plate were poorly developed. In addition, sclerotization and pigmentation were reduced and ocell lacking. The secondary antennal sensoria were also malformed. These findings clearly (1) demonstrate that kinoprene can be employed as a JH mimic to alter the normal programming of the epidermal cells in alatiform nymphs and (2) indicate that JH plays an important role in aphid morphogenesis and polymorphism. The differential responses of the four alatiform nymphal instars suggest that elevated JH levels during the first and second instars are particularly important in inhibiting wing development. To determine the prenatal effects of JH on wing development and morphogenesis, kinoprene was also administered to newly ecdysed apterous adults. Even though conditions favoured alate production, 75% of the offspring produced by kinoprene-treated virginoparae developed into normal apterae. This suggests that elevated JH titers in maternal haemolymph inhibit wing development and promote development of apterae. Topical application of the anti-allatotropin, precocene-II, had variable effects on apteriform nymphs and adults. In all stages, precocene produced a significant decline in larvi-position. The effects were more pronounced in first and second instar apteriform nymphs and apterous adults than in third and fourth instar nymphs. When kinoprene was applied to these insects, larviposition increased significantly after 2 days. The findings demonstrate that JH stimulates reproduction in viviparous morphs of persicae. / Land and Food Systems, Faculty of / Graduate

Myzus persicae (Sülzer), commonly known as the green peach aphid (GPA), is a polyphagous insect that can infest over 100 families of economically important plants and is major pest for vegetable crops. This study utilizes the Arabidopsis-GPA model system with the aim to elucidate the role of the plant disaccharide trehalose in providing defense against GPA. This study demonstrates a novel role for TPS11 in providing defense against GPA. TPS11 expression was found to be transiently induced in Arabidopsis plants in response to GPA infestation and the TPS11 gene was required for curtailing GPA infestation. TPS11, which encodes for trehalose phosphate synthase and phosphatase activities, contributes to the transient increase in trehalose in the GPA infested tissues. This work suggests that TPS11-dependent trehalose has a signaling function in plant defense against GPA. in addition, trehalose also has a more direct role in curtailing GPA infestation on Arabidopsis. This work also shows that TPS11 is able to modulate both carbohydrate metabolism and plant defenses in response to GPA infestation. the expression of PAD4, an Arabidopsis gene required for phloem-based defenses against GPA, was found to be delayed in GPA infested tps11 mutant plants along with increased sucrose levels and lower starch levels as compared to the GPA infested wild type plants. This work provides clear evidence that starch metabolism in Arabidopsis is altered in response to GPA feeding and that TPS11-modulated increase in starch contributes to the curtailment of GPA infestation in Arabidopsis.