Effect of spinosad and predatory mites on control of Frankliniella occidentalis in three strawberry cultivars

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major pest of strawberry, Fragaria × ananassa Duchesne (Rosaceae). Spinosad is highly efficacious against F. occidentalis, and spinosad is believed to be compatible in an integrated pest management program. This study determined whether F. occidentalis could be controlled with predatory mites [Typhlodromips montdorensis (Schicha), Neoseiulus cucumeris (Oudemans) (both Acari: Phytoseiidae), and Hypoaspis miles (Berlese) (Acari: Laelapidae)] and spinosad in strawberry. In the glasshouse, three strawberry cultivars (Camarosa, Camino Real, and Albion) were sprayed once with spinosad at the recommended rate (80 ml 100 l^?1 rate, 0.096 g a.i. l^?1) or with water (control). Thrips adults were released onto plants 24 h after spraying and predatory mites released 6 days later. Spinosad significantly reduced thrips numbers compared with water. All three mite species reduced F. occidentalis numbers, and spinosad had no effect on predatory mites. Though H. miles could not be counted, the numbers of thrips in treatments with H. miles were lower than those in treatments without the mite. Thrips numbers were lowest on Camino Real and highest on Camarosa. These results suggest that the use of Camino Real with spinosad applications followed by releases of predatory mites can significantly reduce thrips numbers.     

Oviposition preference,larval performance and adaptation of Trichoplusia ni on cabbage and cotton

Most female herbivores ensure to lay eggs where their offspring can develop successfully. The oviposition preferences of females affect strategies in pest management. In this study, the performance of two cohorts of Trichoplusia ni larvae on cabbage and cotton (after they had been transferred from their original host plants) were investigated. The preferences of female moth ovipositing and larval feeding on these two host plants were observed. The results indicated that plants significantly affected oviposition preference of the female adults and development and survival of larvae of T. ni. All females preferred to lay eggs on cabbage than cotton regardless from which host they originated. The detrimental effects of cotton on the development and survival of T. ni larvae originated from cabbage (CaTn) increased with the increase of the larval age when they were transferred. In addition, the host plant change did not significantly affect the development and survival of larvae of T. ni originating from cotton (CoTn). Larvae of CaTn preferred cabbage plants as compared to cotton plants, whereas larvae of CoTn did not show a significant choice. Although the adult females preferred laying eggs on cabbage, they did not show preferences between cotton and cabbage in a Y‐tube olfactometer test. The hypothesis of oviposition preference and performance of larvae was supported by the results of CaTn, whereas they not supported by those from CoTn. Based on these results, the strategy to manage this serious pest was discussed.     

草地贪夜蛾在不同小麦品种上的取食选择性和适应性及其与叶片生化物质含量的关系

[目的]测定草地贪夜蛾Spodoptera frugiperda在不同小麦品种上的取食选择性及适应性,探索害虫为害与小麦品种间的关系,明确黄淮海麦区主栽小麦品种对草地贪夜蛾的抗性水平,为麦田抗虫品种布局和害虫综合防治提供理论依据.[方法]比较了草地贪夜蛾1和3龄幼虫对15个小麦品种的取食选择性,初步筛选出1和3龄幼虫取...     

Influence of Trichomes in Strawberry Cultivars on the Feeding Behavior of <Emphasis Type="Italic">Chaetosiphon fragaefolii</Emphasis> (Cockerell) (Hemiptera: Aphididae)

Chaetosiphon fragaefolii (Cockerell) (Hemiptera: Aphididae) is the predominant aphid in strawberry (Fragaria × ananassa Duchesne) production systems in Brazil. This pest species directly damages the plants and is also responsible for spreading viruses. Further, C. fragaefolii often renders strawberry cultivation unviable, because of its high reproductive rate, as well as the large number of individuals generated through parthenogenesis. The present study aimed to (1) evaluate the feeding behavior of C. fragaefolii in four strawberry cultivars (Albion, Aromas, Camarosa, and San Andreas) and (2) identify the resistance factors associated with the number and type of trichomes in the cultivars, and also its effect on the feeding behavior of C. fragaefolii, using the electrical penetration graph (EPG) technique. The results revealed an intrinsic relationship between the number of trichomes on the cultivar and feeding behavior of C. fragaefolii. A higher number of trichomes, both tector and glandular, was observed in Albion compared to that of other cultivars, resulting in a longer no probing (Np) period per insect, and a longer Np phase. A relatively short phloem phase and ingestion time of the phloem sieve elements were also observed in Albion. These results suggest that the trichomes act as a physical barrier creating difficulties for C. fragaefolii to feed, thereby altering its feeding behavior in the four cultivars studied.     

Biology of the Two-Spotted Spider Mite on Strawberry Plants

The two-spotted spider mite, Tetranychus urticae Koch, is commonly found on strawberry crops (Fragaria x ananassa). Strawberry plants have defensive mechanisms, which in turn influence the behavior of herbivores. The oviposition and development of the two-spotted spider mite were evaluated on the leaf disks of the cultivars ‘Aromas,’ ‘Camarosa,’ ‘Camino Real,’ ‘Diamante,’ ‘Diamante 10,’ ‘Diamante 50,’ ‘Festival,’ and ‘Seascape.’ It was observed that on cultivars such as ‘Aromas,’ ‘Camarosa,’ and ‘Seascape,’ immature survivorship was higher, but no difference was found during the developmental period from egg to adult of T. urticae. The immature development time was also longer on ‘Camarosa.’ Females laid more eggs on ‘Seascape’ (8.4 eggs/day), and the least on ‘Camarosa’ (1.0 egg/day). Mortality was higher at the larval stage and reached more than 50% in three cultivars ‘Camarosa,’ ‘Diamante,’ and ‘Seascape.’ Thus, the cultivars ‘Camarosa,’ ‘Diamante,’ and ‘Seascape’ were the ones that mostly affected the survival, development, and reproduction of T. urticae.     

Effects of leaf pubescence in Salix borealis on host- plant choice and feeding behaviour of the leaf beetle, Melasoma lapponica

Density of leaf trichomes in Salix borealis affected both the choice of individual host plants and feeding behaviour of adults and last instar larvae of the willow feeding leaf beetle, Melasoma lapponica. Beetles clearly preferred shaved disks to unshaved ones taken from the same leaf; this preference was highest in leaves of the most pubescent plants. High leaf pubescence explained the low preference for willow clones from the high density site in among-site preference trials; shaving significantly increased the consumption of these pubescent willow clones. In no-choice experiments, the food consumption by both adults and last instar larvae decreased with an increase in leaf pubescence. The time budget of adults did not depend on leaf pubescence of the host plants, however adults compelled to feed on highly pubescent plants changed their feeding sites twice as often as on less pubescent willow clones. Larvae feeding on highly pubescent plants spend moving three times as much time as larvae feeding on less pubescent plants. Combined with our earlier observations on the increase in leaf pubescence in the year(s) following defoliation, these data suggest that leaf hairiness may have contributed to the delayed induced resistance in S. borealis by disturbing the feeding behaviour of M. lapponica.     

The role of glandular and non-glandular trichomes in the negative interactions between strawberry cultivars and spider mite

In tropical countries, spider mite (Tetranychus urticae Koch) is a major pest of strawberries. This pest is mainly controlled by the application of pesticides. Use of pest-resistant cultivars is a healthy and environment-friendly alternative to pesticide use. This paper describes the role of glandular and non-glandular trichomes in the interaction between strawberry cultivars and spider mite. The methodology used in this study was based on two bioassays. First, the thumbtack bioassay of Weston and Snyder was used to differentiate strawberry cultivars in terms of the distance travelled by the mites. Second, different types of trichomes present on the abaxial surface of the strawberry leaves were identified and counted. The results of this study showed a significantly negative correlation between the distance travelled by the spider mites and the density of glandular trichomes on the strawberry plant. The cultivars Camino Real and Dover had the highest densities of glandular trichomes and the shortest distance travelled by the mites. In contrast, the cultivars Ventana and Toyonoka had the lowest density of glandular trichomes and the longest distance travelled by the spider mites. The high density of glandular trichomes might have been responsible for the spider mite non-preference to the Camino Real and Dover strawberry cultivars, whereas the non-glandular trichomes minimally contributed to this non-preference. The results of this study affirm the role of glandular trichomes in negative interactions between strawberry and spider mites.     

Response of six strawberry (Fragaria x ananassa Duch.) cultivars to the root lesion nematode (Pratylenchus penetrans Filipjev and Schurmanns Stekhoven)

In the Philippines, strawberry is grown only in Benguet Province because of its unique climatic conditions. It has been a lucrative source of income for Benguet farmers and adds to the revenue of Benguet Province. The root lesion nematode, Pratylenchus penetrans is an economically important pest of strawberry in the area. It can cause substantial losses to strawberry growers, both by reducing vegetative plant growth and by reducing strawberry yields. The nematode has a very wide host range and hence, is not readily controlled by crop rotation. An alternative approach which growers may wish to consider trying is planting of strawberry varieties which are either resistant or tolerant to this nematode. The relative susceptibility/tolerance of six strawberry cultivars to the root lesion nematode, P. penetrans was evaluated under greenhouse and field conditions. Inoculation of 500 nematodes/pot did not significantly affect the fresh top weight, fresh root weight, and yield of strawberry cultivars Festival, Whitney, Winterdawn, Earlibrite, and Camarosa. The said cultivars had significantly higher number of nematodes recovered from the roots. On the other hand, the highest strawberry yield was recorded in cv Sweet Charlie, however, this was significantly reduced by nematode inoculation .Surprisingly, the number of nematodes recovered from the roots of this cultivar was significantly the lowest among the cultivars tested. Results of the field experiment showed that strawberry cv Sweet Charlie gave the highest marketable yield which was significantly different from the rest of the cultivars tested. This was followed by Festival, and Earlibrite. On the other hand, Camarosa and Whitney gave significantly lower yield than the above cultivars but significantly higher than Winterdawn. In terms of nematodes recovered from the roots, the highest was noted in Whitney, followed by Sweet Charlie and Earlibrite. The lowest was obtained from Camarosa, followed by Festival and Winterdawn. Based on the results of the greenhouse experiment, Festival, Whitney, Winterdawn, Earlibrite and Camarosa can be considered tolerant while Sweet Charlie was slightly susceptible to P. penetrans. However, based on the field trial, Sweet Charlie, Festival and Earlibrite were tolerant while Whitney, Camarosa and Winterdawn were slightly susceptible.     

Variation in abundance and feeding impact of tarnished plant bug (Hemiptera: Miridae) for different cultivars of strawberry: role of flowering phenology and yield attributes

The current study evaluated whether flowering phenology and yield attributes of different strawberry cultivars affect the abundance and feeding impact of tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), as well as behavioral decisions made by feeding nymphs and ovipositing adults. The distribution of emerged nymphs in cage experiments involving nine different cultivars of June-bearing strawberry cultivars suggests that females lay more eggs on plants with numerous flower receptacles, while cultivar per se did not influence their oviposition behavior. A large number of nymphs emerged from receptacles of strawberry plants, while the distribution of emerged nymphs among receptacles, petioles, leaves, and stems varied for different cultivars. These results suggest that the relative intensity of damage caused by ovipositing females may vary for different cultivars. Foraging nymphs did not exhibit a preference for any strawberry cultivar per se, although the abundance of nymphs increased with the weight of receptacles, especially for late instars. Evaluating the density and feeding impact of L. lineolaris for different cultivars under field conditions revealed that some host plant attributes affect the abundance of plant bugs, such as early flowering season and high productivity. Decreasing number of emerged nymphs per flower per plant with increasing density of receptacles per plant suggests that females lay relatively more eggs per receptacle on plants with few receptacles; this pattern of oviposition may explain, in part, why patches with low density of plants typically have high incidence of damage. Planting a high yielding early season cultivar such as 'Cavendish' may contribute to reduce the incidence of damage by L. lineolaris.     

Susceptibility of strawberry cultivars to the vine weevil Otiorhynchus sulcatus (Coleoptera: Curculionidae)

Abstract 1 The feeding preference of vine weevil, Otiorhynchus sulcatus (Fabricius), adults for foliage from 21 commercial cultivars of strawberries is investigated using binary choice tests with leaf disks, using ‘Honeoye’ as a standard against which all other cultivars are compared. ‘Delmarvel’, ‘Idea’, ‘Lester’, ‘Primetime’ and ‘Seneca’ are not preferred. 2 Variation in leaf nitrogen content is correlated with feeding preference, but does not explain all the variation, because outliers exist for both preferred and nonpreferred cultivars. 3 Removal of leaf hairs with adhesive tape permits their role in deterrence to be evaluated. Eight of the 21 cultivars have deterrent leaf hairs. Paradoxically, some highly preferred cultivars (e.g. ‘Latestar’ and ‘Tristar’) have deterrent leaf hairs, and four of the five nonpreferred cultivars lack significantly deterrent leaf hairs. 4 The 21 tested cultivars do not differ in their suitability for vine weevil larval development. 5 Differences in cultivar susceptibility to vine weevil in the field may involve interactions between the palatability and nutritional value of foliage, which influence fecundity and egg placement, and the tolerance of strawberry plants to larval feeding, determined by root biomass. The nonpreference traits found in the foliage of commercial cultivars of strawberry are present by chance. Accordingly, further selective breeding to enhance strawberry varietal tolerance to vine weevils may be possible.     

莲草直胸跳甲的空间选择与性别分化

【背景】莲草直胸跳甲是空心莲子草的专一性天敌,成功地大量繁殖是其大规模应用于空心莲子草生物防治的必要条件,为了更好地开展莲草直胸跳甲的室内大量繁殖,明确其不同虫态对空心莲子草空间的选择性具有重要意义。【方法】本研究调查了莲草直胸跳甲成虫取食与产卵、幼虫取食、老熟幼虫化蛹的空间选择性,并分析了空心莲子草茎秆直径对幼虫化蛹空间选择、蛹羽化率和羽化成虫性别分化的影响。【结果】雌雄成虫均嗜好栖息于空心莲子草幼嫩的顶叶,位于顶叶的雌、雄成虫数量分别占整株的62.9%和63.3%;成虫偏好将卵产在第2节叶片上,比例高达41.2%;幼虫主要集中于上部3节的叶片上取食,占84.8%;老熟幼虫化蛹前在茎秆上蛀孔后钻入茎秆中化蛹,其不在第1节茎秆内化蛹,化蛹主要选择在3～5节,其中在第4节茎秆内化蛹量最高,达1.0头.节-1;老熟幼虫在1～5节茎秆内的化蛹量与空心莲子草茎秆直径具有显著相关性（y=-19.209x2＋16.66x＋2.6737,R2=0.841）;羽化成虫的雌雄性比则与茎秆直径呈显著正相关（y=5.5704x-1.1718,R2=0.914）。【结论与意义】莲草直胸跳甲成虫和幼虫均偏好在空心莲子草上部的叶片取食,老熟幼虫化蛹则偏好中部较粗壮的茎节,因此,培育茎秆较粗且老化程度较低的空心莲子草是实现莲草直胸跳甲大量饲养的重要途径。本研究可为优化人工大量饲养繁殖莲草直胸跳甲的条件提供数据支持。     

烟粉虱成虫对黄瓜叶龄的喜好性及与后代发育适合度间的关系

在室内采用笼罩和发育测定方法,研究了烟粉虱成虫对黄瓜叶龄的喜好性及其与后代生长发育、存活之间的关系,同时调查了叶毛密度与成虫喜好性之间的相关关系。结果表明(1)烟粉虱成虫比较喜欢在黄瓜植株的中部叶片取食和产卵。(2)叶龄对烟粉虱的存活率没有显著影响,对烟粉虱的发育历期只在卵期和若虫四龄期表现出显著影响,对其他龄期或整个世代均没有显著影响。(3)叶毛密度随着叶龄的增大而顺次显著减小;在接虫初始阶段,烟粉虱成虫的叶片选择性与叶毛密度成显著负相关关系,但72h后具有中等叶毛密度的叶片上的成虫数量和着卵量均显著高于叶毛密度较大或较小的叶片。研究结果对培育抗烟粉虱的黄瓜品种和改进烟粉虱的防治措施具有一定指导意义。     

Host race formation in the meadowsweet and strawberry feeding leaf beetle Galerucella tenella

We investigated host race formation in Galerucella tenella, a leaf beetle which feeds preferentially on meadowsweet (Rosaceae) in its natural habitats, but has become an important pest on strawberry (Rosaceae) in agricultural areas. Beetles from two isolated sites (Skeppsvik in Sweden and Solf in Finland) were compared with respect to preference and performance. At Skeppsvik the beetles were found feeding on meadowsweet, while at Solf large populations only develop in strawberry plantations, despite the presence of meadowsweet.In reciprocal field transplantations and laboratory bioassays, beetles from both sites discriminated against their foreign host, using their natal plant to a significantly higher degree for both egg laying and feeding, but with one interesting exception, namely that beetles from Solf increased their use of and even preferred meadowsweet for feeding in the laboratory. This increased use of meadowsweet by adult Solf beetles in the laboratory (without conspecific competitors) may be attributed to a density-dependent strategy, whereby mothers avoid pre-emptying the nutritional resources of the plants that will host their offspring in cases where no competitors are present.Larval fitness did not differ significantly between host plants, although larval survival of Solf beetles was halved when reared on their non-natal host plant (meadowsweet). Although beetles from both sites preferred to oviposit on their local host plant, our results provide little evidence that this presumed adaptation has to do with the nutritional quality of the plants involved. Instead, we suggest that other factors associated with the plants, such as enemy-free space and resistance to drought may be more important selective agents, shaping host preference in the field.     

Feeding preference of three lady beetle predators of the hemlock woolly adelgid (Homoptera: Adelgidae)

In a laboratory study, we tested the feeding preferences of three coccinellid predators of hemlock woolly adelgid, Adelges tsugae Annand, an introduced pest of hemlock in the eastern United States. The species tested were Sasajiscymnus tsugae Sasaji & McClure (formerly Pseudoscymnus tsugae) from Japan, Scymnus ningshanensis Yu & Yao from China, and Harmonia axyridis (Pallas), a generalist species introduced from Asia that is currently widespread in eastern hemlock, Tsuga canadensis Carriere, forests. We measured the feeding preference of each beetle species when given the choice of A. tsugae and either 1) Pineus strobi (Hartig) on Pinus strobus L.; 2) Adelges laricis Vallot on Larix decidua Mill.; 3) Adelges cooleyi (Gillette) on Pseudotsuga menziesii (Mirb.) Franco; or 3) Paraprociphilus tessellatus (Fitch) on Alnus serrulata (Ait.) Willd. We evaluated beetle preference for adults, nymphs, and eggs of each prey species. Generally, when adult or nymphal prey stages were compared, S. tsugae preferred A. tsugae adults to P. strobi, A. cooleyi, A. laricis, and P. tessellatus. S. ningshanensis showed less preference between adelgid species, but it did not prefer P. tessellatus nymphs. When preferences for adelgid eggs were assayed, S. tsugae and S. ningshanensis showed no preference between A. tsugae and A. cooleyi or P. strobi, but S. tsugae did prefer A. tsugae to A. laricis. Larvae of S. tsugae were unable to survive on P. tessellatus nymphs. H. axyridis adults readily consumed both A. tsugae and P. tessellatus, but H. axyridis larvae did not complete their life cycle on A. tsugae. Our host range tests suggest that S. ningshanensis and S. tsugae may feed on several species of Adelgidae and that A. tsugae is often preferred.     

Vector preference and host defense against infection interact to determine disease dynamics

Vector preference based on host infection status has long been recognized for its importance in disease dynamics. Prior theoretical work has assumed that all hosts are uniformly susceptible to the pathogen. Here we investigated disease dynamics when this assumption is relaxed using a series of vector–host epidemiological compartment models with variable levels of host resistance or tolerance to infection – collectively termed defense. In our models, vectors cannot acquire the infection from resistant hosts but can acquire from tolerant hosts. Specifically, we investigated the interacting effects of vector preference and host defense in a series of single‐ and two‐patch models. Results indicate that resistant host types generally reduce disease prevalence and pathogen spillover, independent of vector preference. The epidemiological consequences of host tolerance, however, depended on vector preference. When vectors preferred diseased hosts, tolerance reduced incidence compared to susceptible hosts; when vectors avoided diseased hosts, tolerance enhanced disease prevalence. Finally, a variation of the model that included preference‐based vector patch leaving rates suggests that both resistance and tolerance can promote pathogen spillover if vectors prefer diseased hosts, because of increased vector dispersal into susceptible patches. Collectively, we found complex, context‐dependent effects of vector preference and host defense on disease dynamics. In the context of management programs for vector‐borne diseases, managers should consider both the precise form of host defense present in a population, breed, or cultivar, as well as vector feeding behavior.     

Preference of Bt‐resistant and susceptible Busseola fusca moths and larvae for Bt and non‐Bt maize

The sustainability of genetically engineered insecticidal Bacillus thuringiensis Berliner (Bt) maize, Zea mays L. (Poaceae), is threatened by the evolution of resistance by target pest species. Several Lepidoptera species have evolved resistance to Cry proteins expressed by Bt maize over the last decade, including the African maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The insect resistance management (IRM) strategy (i.e., the high‐dose/refuge strategy) deployed to delay resistance evolution is grounded on certain assumptions about the biology and ecology of a pest species, for example, the interactions between the insect pest and crop plants. Should these assumptions be violated, the evolution of resistance within pest populations will be rapid. This study evaluated the assumption that B. fusca adults and larvae select and colonize maize plants at random, and do not show any preference for either Bt or non‐Bt maize. Gravid female B. fusca moths of a resistant and susceptible population were subjected to two‐choice oviposition preference tests using stems of Bt and non‐Bt maize plants. Both the number of egg batches as well as the total number of eggs laid on each stem were recorded. The feeding preference of Bt‐resistant and susceptible neonate B. fusca larvae were evaluated in choice test bioassays with whorl leaf samples of specific maize cultivars. Although no differential oviposition preference was observed for either resistant or susceptible female moths, leaf damage ratings indicated that neonate larvae were able to detect Bt toxins and that they displayed feeding avoidance behaviour on Bt maize leaf samples.     

南方小花蝽在不同试验空间对西花蓟马的捕食及搜寻效应

【背景】南方小花蝽是一类很有利用前景的捕食性天敌,而有关其在不同捕食空间下对我国局部地区暴发成灾的重要入侵害虫西花蓟马捕食控制效能的研究较少。【方法】在实验室条件下比较研究了南方小花蝽成虫在不同试验空间对西花蓟马成虫、若虫的捕食选择性、捕食功能反应与搜寻效应。【结果】南方小花蝽成虫对西花蓟马若虫的捕食选择性强于成虫;在相同的试验空间,南方小花蝽成虫的日均捕食量随猎物数量的增加而增大,其对西花蓟马成虫和若虫的捕食量在猎物数量为每指形管中60头时最大,分别为15.90和19.30头;而搜寻效应随猎物数量的增加而降低。在各供试条件下,捕食功能反应均符合Holling Ⅱ型方程;南方小花蝽成虫在小饲养容器中对西花蓟马若虫的瞬时攻击率最大,为1.2794;而在大饲养容器中对西花蓟马成虫的瞬时攻击率最小,仅为0.3506,其处理1头西花蓟马成虫的时间约需0.0402d,而处理1头若虫的时间仅需0.0242d。在相同的猎物数量下,南方小花蝽成虫在大饲养容器中对西花蓟马的日均捕食量均低于其在小饲养容器中对西花蓟马的日均捕食量。【结论与意义】南方小花蝽对西花蓟马有很强的捕食效能,对西花蓟马的种群消长具有一定控制作用。本研究旨在为应用南方小花蝽防治西花蓟马积累资料,同时为西花蓟马的综合治理奠定理论基础。     

Ovipositional preferences, damage thresholds, and detection of the tomato-potato psyllid Bactericera cockerelli (Homoptera: Psyllidae) on selected tomato accessions

The tomato-potato psyllid Bactericera [Paratrioza] cockerelli (Sulc) has recently caused losses exceeding 50% on fresh market tomatoes in California and Baja, Mexico by injecting a toxin that results in a condition known as 'psyllid yellows'. The objectives of this study were to: (i) document oviposition preferences on a range of tomato cultivars; (ii) determine threshold levels for psyllid densities that would cause psyllid yellows on tomatoes within the first three weeks following transplanting; and (iii) identify the most important 'psyllid yellows' symptoms that might be used in surveying and monitoring for this pest. Plant lines tested included the commonly-planted commercial cultivars 'Shady Lady' and 'QualiT 21', an older, previously commercial cultivar '7718 VFN', a common cultivar planted by consumers 'Yellow Pear', and a wild type plant accession, PI 134417. When given a choice, psyllids significantly preferred 'Yellow Pear' and avoided PI 134417 for oviposition. Under no-choice conditions psyllids laid significantly fewer eggs on PI 134417, but all the other plant lines were equally good substrates for laying eggs. Thus, oviposition preference is not likely to provide a functional management strategy in large plantings. On 'Shady Lady', psyllids preferred to oviposit on plants already infested with adults. On both 'Shady Lady' and '7718 VFN' oviposition was significantly greater on plants previously infested by nymphs as compared to uninfested control plants. This suggests that, at least for some cultivars, there is a physiological change in plant attractiveness following psyllid feeding. 'Yellow Pear' and 'QualiT 21' were relatively tolerant of psyllids, requiring 18 nymphs per plant to produce the disease symptoms. Only eight nymphs per plant were needed on 'Shady Lady' and '7718 VFN'. For all cultivars, the pest density showed strong correlations with measurements such as the number of yellowing leaves and leaflets and distorted leaves, which were as good as or better than the first factor extracted from principal component analysis. Therefore, such measurements have the potential to simplify field surveys.     

Diamondback moth oviposition: effects of host plant and herbivory

The oviposition behaviour of Plutella xylostella L. (Lepidoptera: Plutellidae) on Chinese cabbage (Brassica rapa L. Pekinensis, cv. Wombok), canola (Brassica napus L. cv. Thunder TT), and cabbage (Brassica oleracea L. Capitata, cv. sugarloaf) (Brassicaceae) was studied in the laboratory. In no‐choice experiments moths laid most eggs on the stems and lower three leaves of cabbage plants, the lower three leaves of canola plants, but on the upper three leaves of Chinese cabbage plants. The effects of conspecific herbivore damage to foliage could be replicated by mechanical damage. When foliage was damaged, injured cabbage and canola plants were preferred for oviposition over intact conspecifics, whereas injured Chinese cabbage plants were less preferred than intact conspecifics. However, when root tissue was damaged, intact cabbage and canola plants were preferred over injured conspecifics, whereas moths did not discriminate between root‐damaged and intact Chinese cabbage plants. Injury to upper leaves significantly affected the intra‐plant distribution of eggs. In cabbage and canola plants, injury to leaf 6 significantly increased the number of eggs laid on this leaf, resulting in a significant decrease in the number of eggs laid on the lower foliage/stem of plants, whereas in Chinese cabbage plants it significantly decreased the number of eggs laid on leaf 6. Following oviposition on intact plants, neonate larvae established the vast majority of feeding sites on leaves 5–8 in all three host plants, indicating that larvae moved a considerable distance from preferred oviposition sites in cabbage and canola plants. The growth rate of neonates fed on leaf‐6 tissue was significantly greater than that of those fed on leaf‐1 tissue; >90% of larvae completed development when fed exclusively on leaf‐6 tissue but no larvae completed development when fed exclusively on leaf‐1 tissue. The study demonstrates the complex and unpredictable interactions between P. xylostella and its host plants and provides a basis from which we can begin to understand observed distributions of the pest in Brassica crops.     

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) chemical control: insecticide efficacy associated with the three consecutive spray strategy

Abstract  After the initial 1993 discovery of Frankliniella occidentalis , western flower thrips, in Australia, temporary chemical control permits were issued to facilitate their insecticidal control. However, these permits were based on established endemic pests of Australian horticulture rather than demonstrated efficacy against F. occidentalis , and laboratory bioassays of Australian field-collected F. occidentalis suggested that some permit application rates were too low to be effective. In 2002 and 2003 field-based trials were carried out in strawberry and lettuce to collect field-generated efficacy data to verify the laboratory conclusions. It was found that by increasing field application rates above the existing permit rate, efficacy was increased, but not for all insecticides and not for all thrips life stages. Increasing the rate of abamectin and endosulfan in strawberry increased control of adults and larvae and increasing the rate of endosulfan in lettuce increased efficacy against larvae only. Spinosad was effective at both rates tested in strawberry, suggesting that the current permit rate could be reduced. The ability to use reduced rates may be useful if used in combination with Integrated Pest Management programs.