Natural enemy impacts on Bemisia tabaci (MEAM1) dominate plant quality effects in the cotton system

1. Plant quality (bottom‐up effects) and natural enemies (top‐down effects) affect herbivore performance. Furthermore, plant quality can also influence the impact of natural enemies. 2. Lower plant quality through reduced irrigation increased the abundance of the cryptic species from the Bemisia tabaci complex [hereafter B. tabaci Middle East Asia Minor 1 (MEAM1)], but not its natural enemies on cotton. It was therefore predicted that lower plant quality would diminish the impact of natural enemies in regulating this herbivore. 3. Over three cotton seasons, plant quality was manipulated via differential irrigation and natural enemy abundance with insecticides. Life tables were used to evaluate the impact of these factors on mortality of immature B. tabaci (MEAM1) over nine generations. 4. Mortality of B. tabaci (MEAM1) was consistently affected by natural enemies but not by plant quality. This pattern was driven by high levels of sucking predation, which was the primary (key) factor associated with changes in immature mortality across all irrigation and natural enemy treatments. Dislodgement (chewing predation and weather) and parasitism contributed as key factors in some cases. Analyses also showed that elimination of sucking predation and dislodgement would have the greatest effect on overall mortality. 5. The top‐down effects of natural enemies had dominant effects on populations of B. tabaci (MEAM1) relative to the bottom‐up effects of plant quality. Effects were primarily due to native generalist arthropod predators and not more host‐specific aphelinid parasitoids. The findings of this study demonstrate the important role of arthropod predators in population suppression and validate the importance of conservation biological control in this system for effective pest control.     

Suitability of some Lantana camara varieties as host plants for the root-feeding flea beetle, Longitarsus bethae

Compatibility between the root-feeding agent Longitarsus bethae Savini & Escalona and the varieties of the target weed Lantana camara L. could influence the chances of successful establishment and effectiveness of this agent as a biocontrol agent of lantana in South Africa. Laboratory experiments were conducted to determine the influence of major South African lantana varieties on feeding, colonization, oviposition preference and larval survival of L. bethae. Feeding preference and the number of adults per plant varied among the varieties. The most damaged and colonized varieties were 150 Orange, 009 Light Pink and 113 Dark Pink. Variety 018 Dark Pink was the least damaged, while 021 Total Pink and 029 White Pink were the least colonized. Females laid the highest number of eggs on variety 150 Orange. The lowest number of eggs was recorded on Australian Richmond Pink and the closely related species Lippia wilmsii. Larval survival differed significantly among the varieties. The highest survival was recorded on 150 Orange. Duration of development also varied significantly among the varieties, with the slowest rate of development recorded on variety 029 Light Pink and the quickest on variety 015 White Yellow. Although variations in female body size were less significant among varieties, males emerging from variety 150 Orange were slightly smaller than those emerged from other varieties. There was a significant tendency for females to select varieties that enhanced the survival of their offspring, which met the predictions of the preference-performance hypothesis. The data suggest that the chances of establishment and successful control of the weed are expected to be much greater on those varieties that were preferred for oviposition and provided better larval performance.     

Biosensors for process monitoring

Summary A short review about the biosensor research activities for bioprocess monitoring in the F.R.G. after its reunification is given. The principles of biosensor applications are presented. In situ sensors and sensors based on the principles of flow injection analysis are studied. Some applications of a four-channel enzyme thermistor, bio-field effect transistors, and immunoanalysis systems for real process monitoring are presented.     

The intracellular concentration of cyclic adenosine 3',5'-monophosphate is constant throughout the cell cycle of Escherichia coli

Abstract Both the intracellular and the extracellular concentration of cyclic AMP increases logarithmically in synchronously growing cultures of Escherichia coli . Thus, cyclic AMP by itself cannot regulate growth and division of the bacterium during the cell cycle.     

How do the consumption and development rates of the conifer specialist Aphidecta obliterata respond to temperature,and is it better adapted to limited prey than a generalist?

This study aimed to address the effect of temperature on the consumption and development rates of Aphidecta obliterata and to compare the responses of Ap. obliterata (specialist) with that of Adalia bipunctata (generalist) to prey limitation. Temperature had a significant and positive effect on the time to egg hatch of Ap. obliterata . The duration of the larval instars was not affected by prey species at 15°C but was significantly shorter, 12.1 days at 20°C compared with 21.1 days at 15°C. The proportion of time spent in each instar, however, was not affected by temperature or prey species, but the duration of the pupal stage was significantly affected by temperature. The average daily consumption of prey aphids increased with instar and was significantly influenced by temperature. There was a significant difference in the length of the pupal stage between coccinellid species but not that of the larval stage. The duration of the larval period increased under conditions of prey shortage. The pupal period of Ap. obliterata was significantly affected by the food regime but not that of Ad. bipunctata . There was a significant interaction between species and food supply on the length of the pupal stage and the larval stage and the final fresh weight achieved by the newly emerged adults. Male adults weighed significantly less than the females in all regimes. Larvae of Ap. obliterata and Ad. bipunctata did not consume any of the alternative prey (Collembola or Psocoptera) provided. There was no significant difference in the consumption of prey between the two coccinellid species. The results suggest that both of these coccinellids are well adapted to low-density-specific prey. There were no obvious differences between the two, which would tend to favour either species in an environment of limited prey.     

Impact of the Arundo scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) on the weight of Arundo donax (Poaceae: Arundinoideae) rhizomes in Languedoc southern France and Mediterranean Spain

Arundo donax L. (Poaceae) is native to Mediterranean Europe and invasive in the Rio Grande Basin of North America. Rhizomes from nine sites in France and Spain infested with a candidate control agent, the armoured scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) weighed 50% less than those from nine sites without scale.     

An order-specific monoclonal antibody to Diptera reveals the impact of alternative prey on spider feeding behavior in a complex food web

Generalist predators have the capacity to restrict pest population growth, especially early in the season before densities increase. However, their polyphagous feeding habits sometimes translate into reduced pest consumption when they target alternative prey. An order-specific monoclonal antibody was developed to examine the strength of trophic connections between Diptera, a major category of non-pest prey, and linyphiid spiders in alfalfa. We report the development and characterization of a monoclonal antibody with order-level specificity to Diptera. This antibody elicited strong absorbance to 22 Diptera from 13 families, no false-positive reactivity to non-dipteran invertebrates, and antigen detection periods following prey consumption that were comparable between spiders. Over 900 field-collected females of the linyphiid spiders Erigone autumnalis and Bathyphantes pallidus were screened for Diptera antigen. Significantly more B. pallidus screened positive for Diptera (40%) compared to E. autumnalis (16%), indicating differential reliance on these prey. In parallel with the collection of spiders for gut-content analysis, prey availability was estimated at web sites. The two spiders exhibited different feeding responses to prey availability. Consumption of Diptera by B. pallidus was strongly correlated with Diptera abundance whilst the availability of other potential prey did not influence predation rates. Conversely, E. autumnalis did not prey upon Diptera in proportion to availability, but increased Collembola activity-density reduced dipteran consumption. Integration of molecular gut-content analysis with precise sampling of prey demonstrated how two closely related linyphiid spiders exhibit different feeding responses to the availability of prey under natural field conditions. Elucidating the feeding preferences of natural enemies is critical to effective incorporation of biological control by generalist predators in the management of agricultural pests.     

Effects of chemical and botanical insecticides used for locust control on Metarhizium anisopliae var. acridum conidia after short- to medium-term storage at 30°C

The short- to medium-term viability and growth of Metarhizium anisopliae var. acridum conidia were investigated when combined with six insecticides, at three different concentrations. All of the insecticides used in this study were suitable for immediate spraying with M. anisopliae var. acridum conidia except for fenitrothion. Fipronil, teflubenzuron, and fenitrothion formulations significantly reduced conidial viability over time. The 10% teflubenzuron treatment caused loss of viability relatively quickly with 9.9% germination after 28 days. Mycelial growth was affected by all the treatments except fenitrothion.     

Postplant Fumigation with DBCP for Citrus Nematode Control in Florida

Eleven citrus groves of diverse varieties and ages infected with Tylenchulus semipenetrans growing in differing soils in Florida were treated with three rates of 1,2-dibromo-3-chloropropane (DBCP) applied by various means. Yield, fruit size, and T. semipenetrans populations in the roots were compared between DBCP-treated and untreated trees over a period of I-3 yr. Maximum fruit size and yield were obtained by applying DBCP at 38-58 kg/hectare (ha) (34-52 lb/acre); whereas best nematode control was with a rate of 77 kg/ha (69 lb/acre). Application of chemical emulsion with a special, drilled, low-profile sprinkler irrigation ground pipe was the most suitable method. Effect of DBCP treatment generally lasted for 3 yr. A mean annual I. 1% increase in fruit diameter, 15.2% increase in fruit yield and a 55.7% decrease incitrus nematode populations was found for D BC P-treated trees in contrast to untreated trees.