Role of canopy height in the resistance of Lycopersicon hirsutum f. glabratum to Tuta absoluta (Lep., Gelechiidae)

The objective of this work was to study the effect of plant canopy height on the resistance of the tomato species Lycopersicon hirsutum to the tomato leafminer Tuta absoluta . Determination of the levels of tridecan-2-one (2-TD) and undecan-2-one (2-UD) in L. hirsutum , as well as the leaf area, density and types of trichomes present in L. hirsutum and L. esculentum were made on apical, medium and basal parts of plant canopy. Correlation of these data were made with the following biological characteristics of T. absoluta : rates of oviposition and egg hatching; length of egg, larval and pupal stages; mortality of the larval and pupal stages; pupal weight; and sex ratio. Levels of 2-TD on leaves of L. hirsutum increased from bottom to top of canopy. Tuta absoluta had higher oviposition and egg hatching, as well as lower mortalities and smaller larval and pupal periods in L. esculentum than in L. hirsutum . Longer pupal period and greater number of small and large mines of T. absoluta were verified in the apical and medium parts of L. hirsutum plants. On the other hand, higher pupal mortality and longer larval periods were obtained in the apical and basal parts of the L. hirsutum plants. Larval mortality was higher in the basal part of those plants. In L. esculentum , leaves from the apical part of the plant promoted lower mortality, longer larval period and greater number of large mines of T. absoluta . However, a shorter pupal period was verified on leaves of the basal part. It appears that an increase in glandular trichome density in L. hirsutum leads to an increase in the levels of 2-TD, which, in turn slows down larval development.     

Role of chemical cues from cotton in mediating host selection and oviposition behaviour in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

We investigated the role of chemoreception in the host selection and oviposition behaviour of Helicoverpa armigera in the laboratory using five cotton genotypes and synthetic volatile terpenes. Female moths oviposited on substrates treated with methanol, ethanol, acetone and pentane extracts of leaves, squares and flowers of the cotton genotypes. Phytochemicals soluble in pentane were the most efficient in eliciting oviposition behaviour. In a two-way bioassay, pentane extracts of leaves or squares of a Multiple Host-plant Resistance genotype (MHR11), Deltapine commercial (DP90), and Smith Red Leaf (SRL) received significantly more eggs than solvent-treated controls. Extracts of squares of the native genotype Gossypium nelsonii did not receive more eggs. Females preferred DP90 and MHR11 to SRL and G. nelsonii. Female moths also laid more eggs on pentane extracts of MHR11 flowers than MHR11 leaves from preflowering, early flowering and peak-flowering plants. In a flight chamber, female moths used olfactory cues at short range to mediate oviposition and discrimination between host plants. Egg-laying, mated females were attracted at a distance (1.5 m) to volatile compounds released by whole plants and odours emanating from filter papers treated with synthetic volatile terpenes. Individually, the terpenes did not stimulate any significant oviposition response. However, there was a significant oviposition response to a mixture of equal volumes of the terpenes ( trans -β-caryophyllene, α-pinene, β-pinene, myrcene, β-bisabolol, and α-humulene). Conversely, antennectomised (moths with transected antennae), egg-laying, mated females did not stimulate any significant oviposition response. The significance of these findings in relation to H. armigera host-plant selection are discussed.     

Oviposition preferences in Grapholita molesta: the relative importance of visual and olfactory cues

The oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), is a major pest of fruit trees worldwide. Females oviposit on the young leaves of peach [Prunus persica (L.) Batsch (Rosaceae)] shoots at twilight, when light intensity changes markedly. Previous researches have shown that the oviposition response of this moth is guided particularly by visual and olfactory cues from host plants. However, the relative importance of visual and olfactory cues in their oviposition preference is largely unknown. As a crepuscular moth, how do choices change as light intensity drops rapidly from day to night? In the present study, through two‐choice behavioural experiments, the oviposition responses of G. molesta to visual and olfactory cues (alone or in combination) from peach shoots were tested at four light intensities ranging from daylight to starlight. Grapholita molesta showed similar oviposition responses to plant cues under 1 000, 100, 1 and 0.01 mW m^?2 illumination. Olfactory cues from peach shoots attracted significantly more oviposition than the negative control, whereas visual cues alone did not. Furthermore, olfactory cues were more attractive than visual cues, and no significant interaction was observed between the responses to the two cues. Our findings indicate that G. molesta females mainly rely on olfactory cues to recognize oviposition sites, regardless of differences in light intensity. These results do not provide evidence for attraction to visual cues, but the possibility that the brightness of leaves might be used to guide oviposition is discussed.     

Relationships of abscised cotton fruit to boll weevil (Coleoptera: Curculionidae) feeding, oviposition, and development

Abscised cotton, Gossypium hirsutum L., fruit in field plots planted at different times were examined to assess adult boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), use of squares and bolls during 2002 and 2003 in the Lower Rio Grande Valley of Texas. Although boll abscission is not necessarily related to infestation, generally more bolls abscised than squares and abundances of fallen bolls were not related to the planting date treatments. During 2003, fallen squares were most abundant in the late-planted treatment. Although large squares (5.5-8-mm-diameter) on the plant are preferred for boll weevil oviposition, diameter of abscised squares is not a reliable measurement because of shrinkage resulting from desiccation and larval feeding. Fallen feeding-punctured squares and bolls were most abundant in late plantings but differences between fallen feeding-punctured squares versus fallen feeding-punctured bolls were found in only one treatment in 2003. During the same year, fallen oviposition-punctured squares were more numerous in the late-planted treatment than in the earlier treatments. Treatment effects were not found on numbers of oviposition-punctured bolls, but fallen oviposition-punctured squares were more common than bolls in the late-planted treatment compared with earlier treatments each year. Dead weevil eggs, larvae, and pupae inside fallen fruit were few and planting date treatment effects were not detected. Living third instars and pupae were more abundant in fallen squares of the late-planted treatment than in the earlier treatments and bolls of all three treatments. This study shows that fallen squares in late-planted cotton contribute more to adult boll weevil populations than bolls, or squares of earlier plantings.     

Effects of kaolin-based particle film application on boll weevil (Coleoptera: Curculionidae) injury to cotton

This study examined a non-insecticidal tactic for suppressing boll weevil, Anthonomus grandis grandis Boheman, damage to cotton, Gossypium hirsutum L. In cage assays, kaolin, a reflective white mineral, applied to excised cotton squares or to the cotton foliage, initially resulted in lower levels of boll weevil injury to squares than nontreated squares. Boll weevil oviposition and feeding on kaolin-treated squares and squares on kaolin-treated cotton plants increased when nontreated squares and cotton plants were in short supply. A laboratory assay and field trials suggested that boll weevils distinguished between cotton plots based on color differences caused by kaolin and this appeared to influence levels of damage to squares. Random sampling in small plots indicated that oviposition damage to squares in plots treated with kaolin was reduced (P < 0.05) compared with nontreated controls, except when rain washed the kaolin off the foliage. Lint yield differences were not detected between the small plots, but the kaolin-treated small plots yielded as much as 2.36 times more cotton lint than a large but unreplicated adjacent nontreated control plot, and up to 1.39 times more than another large but unreplicated adjacent plot sprayed twice with preemptive applications of azinphosmethyl when cotton squares were first developing (pinhead stage). Potentially important avenues for future research on boll weevil injury suppression using kaolin are discussed.     

山胡椒及其挥发物对马铃薯块茎蛾产卵选择的影响

【目的】为了确定山胡椒Lindera glauca(Sieb.Zuce)是否对马铃薯块茎蛾Phthorimaea operculella Zeller的产卵有驱避作用。【方法】利用选择性产卵试验方法在室内分别测定了山胡椒的完整果实、压碎果实、根以及不同浓度(0.25~4.0 g E/m L)的压碎山胡椒果实正己烷提取物对马铃薯块茎蛾产卵选择性的影响;在模拟仓库内测定了压碎的果实对其产卵的影响;进而在室内测定了柠檬醛、沉香醇、香叶醇和α-水芹烯不同浓度(0.00075~0.012 g/L)的溶液对其产卵选择性的影响。【结果】山胡椒完整果实、压碎果实、根在室内对马铃薯块茎蛾产卵具有驱避效果,其中压碎果实的产卵驱避效果最好,20 g压碎果实的产卵驱避率可达93.7%。山胡椒压碎果实正己烷提取物在0.5~4.0 g E/m L的浓度范围内随着浓度的升高,产卵驱避效果逐渐增强。在模拟仓库内20 g压碎的果实产卵驱避率是82.5%;0.003~0.012 g/L的柠檬醛,0.012 g/L沉香醇,0.00075~0.012 g/L的香叶醇,0.003~0.012 g/L的α-水芹烯对马铃薯块茎蛾产卵有显著的驱避效果。【结论】山胡椒及其挥发物对马铃薯块茎蛾产卵有驱避效果。     

Bioassays on selection and feeding responses of Holotrichia oblita adults to different plant species

Bioassays on selection and feeding responses of Holotrichia oblita adults to different plant species were conducted both in laboratory and under field conditions. The selection response bioassay showed that the adults were significantly attracted to Ricinus communis. In paired tests of the field cages, more than 60% adults were attracted to R. communis plants, while only 35.55%, 34.45%, 33.35%, and 26.65% were attracted to plants of Glycine max, Arachis hypogaea, Ipomoea batatas, and Gossypium hirsutum, respectively. In the laboratory, the selection response percentage of the adults to R. communis leaves reached up to 93% in the presence of other host plant leaves and still arrived at 70% in the absence of other host plant leaves. Feeding deterrence bioassay showed that the adults preferred to I. batatas leaves with 229.90 ± 4.25 mg leaf consumption and 41.30 ± 5.19 mg faeces excretion after 12 h, followed by the leaves of G. hirsutum and A. hypogaea. The adult did not prefer leaves of R. communi with only 7.10 ± 0.23 mg leaf consumption and corresponding 4.00 ± 0.84 mg fecal excretion. In summary, all experimental results suggested that the attraction of H. oblita adults to R. communi is not triggered for feeding.     

Bioassays on selection and feeding responses of Holotrichia oblita adults to different plant species

Bioassays on selection and feeding responses of Holotrichia oblita adults to different plant species were conducted both in laboratory and under field conditions. The selection response bioassay showed that the adults were significantly attracted to Ricinus communis. In paired tests of the field cages, more than 60% adults were attracted to R. communis plants, while only 35.55%, 34.45%, 33.35%, and 26.65% were attracted to plants of Glycine max, Arachis hypogaea, Ipomoea batatas, and Gossypium hirsutum, respectively. In the laboratory, the selection response percentage of the adults to R. communis leaves reached up to 93% in the presence of other host plant leaves and still arrived at 70% in the absence of other host plant leaves. Feeding deterrence bioassay showed that the adults preferred to I. batatas leaves with 229.90 ± 4.25 mg leaf consumption and 41.30 ± 5.19 mg faeces excretion after 12 h, followed by the leaves of G. hirsutum and A. hypogaea. The adult did not prefer leaves of R. communi with only 7.10 ± 0.23 mg leaf consumption and corresponding 4.00 ± 0.84 mg fecal excretion. In summary, all experimental results suggested that the attraction of H. oblita adults to R. communi is not triggered for feeding.     

Effects of recent experience on foraging in tephritid fruit flies

In field-cage studies, we investigated how the foraging behavior of tephritid fruit flies is modified by experience immediately prior to release on host plants. We observed females of a relatively monophagous species,Rhagoletis mendax (blueberry maggot fly), an oligophagous species,Rhagoletis pomomella (apple maggot fly), and a polyphagous species,Ceratitis capitata (Mediterranean fruit fly). Just prior to release on a host plant, the following kinds of stimuli were supplied: (1) single oviposition in a host fruit, (2) contact with 20% sucrose, (3) contact with a mixture of protein food (bird feces and sucrose), (4) contact with water, and (5) a walk over a host-plant leaf. When flies foraged on host plants without resources, search was most intensive (as measured by number of leaves visited) following a single oviposition in fruit, but residence time generally was the same following exposure to sugar, protein, and fruit stimuli.Rhagoletis mendax andC. capitata females visited the fewest leaves following exposure to water or host leaves, whereasR. pomonella foraged equally intensively following exposure to food stimuli, water, or leaves. On host plants containing resources (fruit and protein food), a single oviposition dramatically increased the number of females of all three species that found fruit compared to females that received experience with food, water or foliar stimuli. We found no significant effect of recent brief experience with any of the stimuli on subsequent attraction to protein food. Overall,C. capitata exhibited a higher propensity to abandon host plants than eitherR. mendax orR. pomonella. We suggest that this may reflect adaptations to differences in distribution of host plants in nature, strategies of dispersal, and host range.     

Effects on oviposition behaviour and larval development of Spodoptera littoralis by herbivore-induced changes in cotton plants

Herbivore feeding induces chemical defence responses in plants. In this study we investigate how herbivore-induced changes in cotton plants, Gossypium hirsutum L., influence the oviposition behaviour and larval development of Spodoptera littoralis Boisd. (Lepidoptera: Noctuidae). In two-choice experiments female moths preferred to oviposit on small plants (3–4 leaves) that had been fed on by 3rd to 4th instar larvae (72%) over non-damaged control plants. However, when using larger plants (8 to 10 true leaves) the preference was reversed, with only 31% of the eggs deposited on the induced plants. The same trend was found with plants that had been given a similar level of damage by 6th instar larvae. However, the difference between the treatments was in both cases smaller with only 60% of the eggs deposited on the preferred plant treatment. If cotton plants subjected to artificial damage were compared with undamaged plants, none of the treatments were preferred for oviposition. No significant difference was found in larval weight, pupal weight, survival, or development time, between larvae reared their entire development on leaves from induced or from non-induced plants.     

Physical and chemical cues affect oviposition by Neoleucinodes elegantalis

Recognition and acceptance of a suitable host plant by phytophagous insects requires the integration of visual, physical and chemical cues. The present study investigates the host cues that a specialist insect integrates to optimize oviposition decisions and whether these cues are weighted in a specific way. The study also determines whether the tomato fruit borer Neoleucinodes elegantalis (Guenée) (Lepidoptera: Crambidae), an important pest on Solanaceae in Brazil, shows a preference for oviposition sites that differ in physical and/or chemical cues. When styrofoam balls are provided as artificial fruits, N. elegantalis deposit significantly more eggs on rough artificial fruits than on smooth ones. Hexane fruit extracts applied to the artificial fruits stimulate female oviposition strongly. Physical and chemical cues also affect the oviposition of females when offered together. Furthermore, certain parts of the artificial fruits are prefered, irrespective of the presence of chemical cues. Both physical and chemical cues affect oviposition decisions; hence, the fruit borer relies on cues of different sensory modalities.     

Efficacy of extracts of Melia azedarach L. callus, leaves and fruits against adults of the sweetpotato whitefly Bemisia tabaci (Hom., Aleyrodidae)

Bioassays with extracts of callus, fruit and leaves of the Chinaberry tree, Melia azedarach L., were performed against adults of Bemisia tabaci (Gennadius). Tissue culture of M. azedarach was carried out in Murashige and Skoog (MS) medium supplemented with indole butyric acid and benzyl adenine. Fresh and frozen leaves or fruits and the callus product were extracted in water or methanol at a ratio of 1 : 5 (w/v) for 48 h. The aqueous and methanol extracts were applied on tomato plants to determine their effect on B. tabaci adults and their corresponding oviposition and consequent adult emergence in comparison with the control, distilled water. Results have shown that extracts of callus and different age classes of M. azedarach leaves and fruits have shown significant repellent activity of 58.9–67.7% and have significantly decreased the oviposition rate of the insect without affecting the adult whitefly emergence in comparison with the control. Aqueous and methanol extracts have shown comparable effects against adult whiteflies indicating a similar efficacy of the two solvents in extracting the bioactive components of Melia . Extracts of frozen samples were found to be as effective against the pest as fresh samples, thus allowing storage of Melia parts to be used in case of shortage. This is the first report of the use of M. azedarach callus against B. tabaci; the M. azedarach callus, leaf and fruit extracts seem to present a potential source for management of B. tabaci .     

Proactive spraying against boll weevils (Coleoptera: Curculionidae) reduces insecticide applications and increases cotton yield and economic return

The current standard practice of two to three preemptive insecticide applications at the start of pinhead (1-2-mm-diameter) squaring followed by threshold-triggered (whenever 10% of randomly selected squares have oviposition punctures) insecticide applications for boll weevil, Anthonomus grandis grandis Boheman, control does not provide a reliably positive impact on cotton, Gossypium hirsutum L., yields in subtropical conditions. This study showed that four fewer spray applications in a "proactive" approach, where spraying began at the start of large (5.5- 8-mm-diameter) square formation and continued at 7- to 8-d intervals while large squares were abundant, resulted in fewer infested squares and 46-56% more yield than the standard treatment at two locations during 2004. The combination of fewer sprays and increased yield made the proactive approach 115-130% more profitable than the standard. The proactive approach entails protection only at the crop's most vulnerable stage (large squares) that, as a source of food, accelerates boll weevil reproduction. In contrast, the standard approach protects early season small squares and later season bolls, both of which contribute less to boll weevil reproduction than large squares. Proaction is an in-season crop protection approach that can be used to increase yield in individual fields during the same season and that could be incorporated into boll weevil eradication strategy that involves later diapause sprays. Because proaction is based on an important relationship between the cotton plant and boll weevil reproduction, the tactic will probably be effective regardless of climate or region.     

Adult response of the almond seed wasp,Eurytoma amygdali, to chemicals from its host and certain nonhosts

Females of the almond seed wasp,Eurytoma amygdali Enderlein (Hymenoptera, Eurytomidae), responded in an olfactometer positively to odours from almond flowers and unripe fruits, but not to almond leaf odours and odours from flowers and unripe fruits of certain other nonhostPrunus species. Males responded to none of these odours. Extracts of undamaged unripe almond fruits (using ethanol, methanol, acetone, hexane, dichloromethane, or petroleum ether) stimulated female aggregation on glass surfaces treated with these extracts; in addition, certain fruit extracts (ethanol, methanol, or acetone) stimulated oviposition. Extracts of undamaged almond leaves (ethanol, methanol, or acetone) and flowers (ethanol or methanol) also stimulated female aggregation and oviposition. Aggregation and oviposition in response to an ethanol extract of almond fruits was intense in females aged 5 to 14 days and from 12∶00 to 18∶00h (photophase between 06∶00 and 20∶00). Certain almond fruit (ethanol, methanol, acetone or hexane) and flower extracts (ethanol or methanol) also provoked female response in the olfactometer. The results strongly suggest that certain chemical stimuli emanating from parts of the almond tree play a major role in host selection and oviposition. Some of the extracts tested may be a good source for the isolation, identification and synthesis of compounds stimulating attraction, aggregation and oviposition in nature. *** DIRECT SUPPORT *** A3414024 00003     

Inter-Specific Differences in Cotton for Nutrient Partitioning from Subtending Leaves to Reproductive Parts at Various Developmental Stages: Consequences for Fruit Growth and Yield

A field study was carried out to unravel the inter-specific differences in cotton for the partitioning of N, P, K, S, Ca, Mg, Na and Cl from the subtending leaves to the reproductive parts of Gossypium hirsutum, G. barbadense and G. arboreum at various developmental stages. Results revealed significant differences among the species for the various parameters studied. Overall there was a greater fresh and dry matter yield of various reproductive parts and subtending leaves of G. hirsutum and G. barbadense than G. arboreum, although the leaf photosynthetic rate was similar. Age-dependent increase in leaf area/leaf mass ratio indicated a greater partitioning of earlier acquired assimilates to the growth of reproductive parts. Results indicated greater partitioning of N, P, S and Ca during later reproductive growth (from boll production to its opening) in G. hirsutum and G. barbadense but during earlier reproductive growth in G. arboreum (from bud up to flower formation) as was evident by decreased subtending leaf/reproductive parts ratio. It is concluded that better N, P, S and Ca partitioning ability of G. hirsutum and G. barbadense at the onset of boll development played a major role in the better yield and good quality fiber characteristics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flight Tunnel Responses of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) to Olfactory and Visual Stimuli

Cohorts of mass-reared, naive Diachasmimorpha longicaudata, parasitoids of tephritid fruit flies, were released in a laminar airflow wind tunnel to study their responses to visual and olfactory stimuli associated with their host habitat. Parasitoids were five times more likely to land on yellow plastic spheres emitting the odor of ripe, guava fruit (Psidium guajava L.) than to spheres emitting clean air. The rate of landing was not modified by the presence of green artificial leaves adjacent to the spheres in the tunnel or by the inclusion of green leaf volatiles emanating with the guava odors. However, hovering activity was twice as frequent around spheres adjacent to artificial leaves than around isolated spheres. Oviposition activity on spheres emitting guava odor was not affected by the presence of artificial leaves nor by green leaf volatiles. This suggests that inexperienced D. longicaudata may be instinctively attracted to foliage and to fruit odor but that landing (arrestment) and oviposition are influenced more by odor than by the appearance of fruit or foliage. D. longicaudata are not instinctively attracted to larvae of Bactrocera dorsalis in the absence of host-habitat stimuli. More wasp activity occurred around oviposition units containing larvae if the odor of ripe/overripe guava was present. Successful wasp reproduction occurred only in units with guava odor.     

颜色对梨小食心虫产卵选择性的影响

梨小食心虫(Grapholitha molesta Busck)是一种重要的果树害虫,早春产卵喜在桃嫩梢叶上,为探明寄主颜色在其产卵选择中的作用,利用彩色卡纸模拟寄主颜色,室内比较了红、粉红、浅粉、橙黄、深黄、浅黄、青绿、深绿、浅绿、蓝、紫、褐色等12种不同颜色基质对其成虫产卵选择性的影响。结果发现:基质颜色对梨小食心虫的产卵选择性有显著影响,其产卵偏嗜浅黄和浅绿色,白色和黑色参比时其产卵选择率分别依次为68.9%、63.8%和64.1%、65.5%,蓝和浅粉色则表现一定的拒避作用,白色和黑色参比时其产卵选择率分别依次为47.7%、40.4%和47.2%、42.7%,且参比色对其产卵选择性影响差异显著。基质颜色对其产卵量亦有显著性影响,无论黑或白色参比,黄、绿颜色上的产卵量均较多,尤其是深黄、深绿和青绿色。基质颜色对1—7日龄梨小食心虫成虫的产卵选择性均有显著影响。白色参比时,2、3日龄蛾对浅绿和浅黄色的产卵选择率显著高于其他颜色;黑色参比时,2日龄时明显偏嗜浅绿色(79.7%),6日龄时明显偏嗜浅黄色(74.8%)。表明寄主颜色在梨小食心虫产卵场所选择中具有重要作用,为其卵期监测和防控中颜色应用乃至进一步揭示其产卵寄主选择机理提供了依据和参考。     

Oviposition‐induced plant cues: do they arrest Trichogramma wasps during host location?

Plants can defend themselves against herbivorous insects before the larvae hatch from eggs and start feeding. One of these preventive defence strategies is to produce plant volatiles, in response to egg deposition, which attract egg parasitoids that subsequently kill the herbivore eggs. Here, we studied whether egg deposition by Pieris brassicae L. (Lepidoptera: Pieridae) induces Brussels sprouts plants to produce cues that attract or arrest Trichogramma brassicae Bezdeko (Hymenoptera: Trichogrammatidae). Olfactometer bioassays revealed that odours from plants with eggs did not attract or arrest parasitoids. However, contact bioassays showed that T. brassicae females were arrested on egg‐free leaf squares excised from leaves with 72 h‐old egg masses, which are highly suitable for parasitisation. We tested the hypothesis that this arresting activity is due to scales and chemicals deposited by the butterflies during oviposition and which are thus present on the leaf surface in the vicinity of the eggs. Indeed, leaf squares excised from egg‐free leaves, but contaminated with butterfly deposits, arrested the wasps when the squares were tested 1 day after contamination. However, squares from egg‐free leaves with 72 h‐old butterfly deposits had no arresting activity. Thus, we exclude that the arresting activity of the leaf area near 72 h‐old egg masses was elicited by cues from scales and other butterfly deposits. We suggest that egg deposition of P. brassicae induces a change in the leaf surface chemicals in leaves with egg masses. A systemic induction extending to an egg‐free leaf neighbouring an egg‐carrying leaf could not be detected. Our data suggest that a local, oviposition‐induced change of leaf surface chemicals arrests T. brassicae in the vicinity of host eggs.