Isolation and characterization of polymorphic microsatellite loci for the horn fly, Haematobia irritans (L.) (Diptera: Muscidae)

The horn fly, Haematobia irritans (L.) (Diptera: Muscidae), is a cosmopolitan livestock pest that has caused a great negative impact on the animal production sector throughout the world. Here, we describe 10 polymorphic microsatellite loci isolated from H. irritans. The number of alleles found ranged from two to eight per locus and the expected heterozygosity from 0.1421 to 0.7702. These loci are potentially useful for the fine-scale genetic characterization of horn fly populations and provide fundamental information for pest management and planning of control programs.     

Molecular interactions of the neuronal GPI-anchored lipocalin Lazarillo

Lazarillo, a glycoprotein involved in axon growth and guidance in the grasshopper embryo, is the only member of the lipocalin family that is attached to the cell surface by a GPI anchor. Recently, the study of Lazarillo homologous genes in Drosophila and mouse has revealed new functions in the regulation of lifespan, stress resistance and neurodegeneration. Here we report an analysis of biochemical properties of Lazarillo to gain insight into the molecular basis of its physiological function. Recombinant forms of the grasshopper protein were expressed in two different systems to test: (1) potential binding of several hydrophobic ligands; (2) protein-protein homophilic interactions; and (3) whether interaction with the function-blocking mAb 10E6 interferes with ligand binding. We tested 10 candidate ligands (retinoic acid, heme, bilirubin, biliverdin, ecdysterone, juvenile hormone, farnesol, arachidonic acid, linoleic acid and palmitic acid), and monitored binding using electrophoretic mobility shift, absorbance spectrum, and fluorimetry assays. Our work indicates binding to heme and retinoic acid, resulting in increased electrophoretic mobility, as well as to fatty acids, resulting in multimerization. Retinoic acid and fatty acids binding were confirmed by fluorescence titration, and heme binding was confirmed with absorbance spectrum assays. We demonstrate that Lazarillo oligomerizes in solution and can form clusters in the plasma membrane when expressed and GPI-anchored to the cell surface, however it is unable to mediate cell-cell adhesion. Finally, by ligand-mAb competition experiments we show that ligand-binding alone cannot be the key factor for Lazarillo to perform its function during axonal growth in the grasshopper embryo. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Microbial combinatorics: a simplified approach for isolating insecticidal bacteria

Bacteria can control pest insects that damage food crops, vector diseases and defoliate trees. Conventionally, isolation of these bacteria has been from soil and sporadically from dead insects. A simplified approach for isolating insecticidal bacteria from soil using the target insect as the selective agent was employed in this study. Instead of isolating single strains of bacteria from soil and testing each individual strain for insect toxicity, mixtures of bacteria present in each soil sample were tested together directly for toxicity using Manduca sexta (Linnaeus) (Lepidoptera: Sphingidae) as a model insect. Thirty-five soil suspensions or bacterial suspensions of the 40 suspensions tested killed at least one M. sexta larva. All but one bacterial culture isolated from dead larvae and retested for toxicity, killed at least one M. sexta larva. Nineteen bacterial strains isolated from larvae killed in the first test, were identical to the bacteria fed to the retested larvae. Of the 19 strains isolated, 14 were identified by 16S rDNA sequencing as belonging to the Bacillus cereus group including three strains that formed crystals that were identified as B. thuringiensis. Of the three other spore-forming strains, two were identified as psychrotrophic B. weihenstephanensis and the third as Lysinibacillus fusiformis. Two others were identified as Enterococcus faecalis. This approach, microbial combinatorics, reduces the number of insects necessary for toxicity screening and associated time and resources compared to conventional methods that first isolate bacteria and then individually test for toxicity as well as a means of discovery of new pathogens using the insect as the selective agent.     

Visual Sensation of an Ethological Stimulus, the Agonistic Display of Betta splendens, Revealed using Multi-Unit Recordings from Optic Tectum

We made multi-unit recordings from the optic tectum of Betta splendens while they viewed the agonistic display of conspecifics. Movement of displaying animals evoked brisk, arrhythmic bursting in tectal units. Particularly high frequency spike bursts coincided with the onset of full display, a behavioral element known to be of ethological significance. These results show that it is possible to obtain informative electrophysiological recordings from optic tectum using behaving conspecifics as stimuli. More frequent use of natural stimuli can be expected to contribute to a greater understanding of the link between the neural substrates of vision and visually guided behavior.     

Scent Marking by Males of the Mediterranean Fruit Fly, Ceratitis capitata (Diptera: Tephritidae)

Males of the Mediterranean fruit fly, Ceratitis capitata (medfly), defend individual leaves as mating territories. While perching, males release an air-borne pheromone (known to attract females) from everted rectal epithelium at the tip of the abdomen. Males also occasionally touch the substrate with the tip of their abdomen. The main objective of the present study was to determine whether such abdomen dipping was a form of intersexual signaling, i.e., whether this action resulted in increased female visitation to the territory. Following observations on the frequency of pheromone calling and abdomen dipping of individually marked males, I ran a standard set of experiments using leaves from four different plant species. Leaves were exposed to varying numbers of (mature) males and females, respectively, for varying durations, and female settlement was compared on exposed versus nonexposed leaves in laboratory cages. Exposing leaves to females had no, or little, influence on female distribution for any of the four plant species. Exposing leaves to males had little influence on subsequent female settlement for orange, coffee, or macadamia trees. However, leaves of the fig tree Ficus bejamina that were exposed to males were much more attractive to females than nonexposed leaves. I then conducted a series of additional tests using fig leaves and found that i) leaf exposure to immature males had no effect on female distribution, ii) leaf exposure to mature males for as little as 90 min increased leaf attractiveness to females, iii) prohibiting males direct contact with the leaf during exposure eliminated any effect on female settlement, and iv) females discriminated between exposed and nonexposed leaves even in physically complex environments (i.e., potted plants). The possible role of abdomen dipping in sexual advertisement of male medflies is discussed.     

A Stilbene Optical Brightener can Enhance Bacterial Pathogenicity to Gypsy Moth (Lepidoptera: Lymantriidae) and Colorado Potato Beetle (Coleoptera: Chrysomelidae)

Stilbene optical brighteners were first investigated to protect biological control agents such as viruses, fungi, and nematodes against ultraviolet light. Some are known to enhance the activity of insect viruses in Lepidoptera. In this work, one stilbene brightener, Tinopal LPW, also increased mortality of gypsy moth and Colorado potato beetle larvae when treated with bacteria/optical brightener combinations. This increase in mortality, however, did not occur for every bacteria/insect combination. In gypsy moth, a significant increase in larval mortality was observed only with Bacillus thuringiensis combined with Tinopal LPW. In Colorado potato beetle, however, the addition of Tinopal LPW increased larval mortality with all bacteria tested (B. thuringiensis, Serratia marcescens, Photorhabdus luminescens, and Chromobacterium sp.). The brightener also decreased the time to kill for these pathogens. This decrease in LT₅₀ was observed not only for bacteria+Tinopal LPW combinations, but also for combinations of Chromobacterium sp. toxin+Tinopal LPW. The mechanism for increase in bacterial toxicity by optical brighteners is compatible with mechanisms proposed for enhancement based on viral/lepidopteran/optical brightener systems that are not dependent on replication.     

Modeling incomplete sterility in a sterile release program: interactions with other factors

Models were constructed for control of a pest species by the release of sterile insects and these models explored the consequences of incomplete sterility. This feature was then coupled with the lack of competitive ability of released insects, the immigration of insects from outside the control area, and the mode of population regulation (density independent vs. density dependent). Using the density-independent models, it was seen that the limits on residual fertility of treated insects become much more stringent when incomplete sterilization is combined with a lack of competitive ability and immigration of insects into the control area. Strong density dependence in the system has a marked moderating effect on the requirements for sterility, competitive ability, and immigration. However, if the density-independent limits on these factors are exceeded, then suppression is possible, but collapse of the pest population is impossible using sterile releases alone. Even suppression might not be satisfactory if these three detrimental factors are prominent. It is suggested that one remedy is the use of the sterile release method in combination with other control methods. Received: January 18, 2001 / Accepted: August 7, 2001