The genetic basis of host preference and resting behavior in the major African malaria vector, Anopheles arabiensis

Malaria transmission is dependent on the propensity of Anopheles mosquitoes to bite humans (anthropophily) instead of other dead end hosts. Recent increases in the usage of Long Lasting Insecticide Treated Nets (LLINs) in Africa have been associated with reductions in highly anthropophilic and endophilic vectors such as Anopheles gambiae s.s., leaving species with a broader host range, such as Anopheles arabiensis, as the most prominent remaining source of transmission in many settings. An. arabiensis appears to be more of a generalist in terms of its host choice and resting behavior, which may be due to phenotypic plasticity and/or segregating allelic variation. To investigate the genetic basis of host choice and resting behavior in An. arabiensis we sequenced the genomes of 23 human-fed and 25 cattle-fed mosquitoes collected both in-doors and out-doors in the Kilombero Valley, Tanzania. We identified a total of 4,820,851 SNPs, which were used to conduct the first genome-wide estimates of “SNP heritability”for host choice and resting behavior in this species. A genetic component was detected for host choice (human vs cow fed; permuted P = 0.002), but there was no evidence of a genetic component for resting behavior (indoors versus outside; permuted P = 0.465). A principal component analysis (PCA) segregated individuals based on genomic variation into three groups which were characterized by differences at the 2Rb and/or 3Ra paracentromeric chromosome inversions. There was a non-random distribution of cattle-fed mosquitoes between the PCA clusters, suggesting that alleles linked to the 2Rb and/or 3Ra inversions may influence host choice. Using a novel inversion genotyping assay, we detected a significant enrichment of the standard arrangement (non-inverted) of 3Ra among cattle-fed mosquitoes (N = 129) versus all non-cattle-fed individuals. Thus, tracking the frequency of the 3Ra in An. arabiensis populations may be of use to infer selection on host choice behavior within these vector populations; possibly in response to vector control. Controlled host-choice assays are needed to discern whether the observed genetic component has a direct relationship with innate host preference. A better understanding of the genetic basis for host feeding behavior in An. arabiensis may also open avenues for novel vector control strategies based on driving genes for zoophily into wild mosquito populations

Host age selection behaviour of Trichogramma aurosum Sugonjaev & Sorokina (Hymenoptera: Trichogrammatidae)

Host age selection in several German strains of Trichogramma aurosum Sugonjaev & Sorokina was examined in laboratory choice tests under direct observation for 90 min., in order to select candidate strains for attempts at controlling the codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae). Experiments were conducted at room temperature by exposing combinations of two host ages (zero vs. 4 and 1 vs. 5-day old) to a single female wasp. Host age did not appear to affect the wasps parasitization behaviour, although they spent longer time drilling on old eggs (4 and 5 days old) compared with fresh ones (0 and 1 day old). This not necessarily means that they preferred fresh eggs over old ones, since both type of hosts were parasitized in the choice test. Possibly an increased mechanical resistance of the chorion of older eggs was responsible for the prolonged drilling time. Mean drumming time was independent of host age. Mean duration of drilling and drumming was in general longest in the first and last egg attacked by all T. aurosum strains tested and for all host ages. Drilling time consumed more than 80% of the mean handling time of all strains tested for all host ages, followed by resting and walking

Occupational Choice of Return Migrants in Moldova

This paper analyses the occupational choice of return migrants. Using the CBSAXA data on different aspects of migration in Moldova, we find that those who stayed illegally in the host country tend to go in wage employment on return to the home country. We also show that relatively better educated tend not be in formal employment, i.e., appear not to participate in the labour market whereas those with relatively lower skills or who obtained worse than expected outcome in the host country are more likely to be wage employed in the home country on return. We discuss intuition of these paradoxical results in the paper.sample selection, return migration, occupational choice, Moldova

A place to grow? Host choice and larval performance of Microplitis similis (Hymenoptera: Braconidae) in the host Spodoptera litura (Lepidoptera: Noctuidae)

Host selection is a key stage in the lifecycle of parasitoids, and is critical to both their function in control and to the maintenance of their population. The solitary endoparasitoid Microplitis similis (Hymenoptera: Braconidae) is a potential biological control agent of Spodoptera litura (F.) larvae (Lepidoptera: Noctuidae). In this study, we examined the preference M. similis exhibits for different instars of the host, host instar effects on parasitoid development, and the weight gain and food consumption of different instars of parasitized larvae. In no-choice tests, parasitization rates were highest in second- and early third-instar larvae, and no fourth- or fifth-instar hosts were parasitized. When provided with a choice of first- to late third-instar host larvae, M. similis preferred to parasitize early third-instar host larvae (41%) with a selection coefficient of 0.37. All morphometric features of wasp offspring increased with increasing age of the host at parasitization. A lower proportion of females emerged from first-instar larvae than any other instar. Parasitized S. litura larvae showed a pronounced reduction in food consumption and weight gain. Microplitis similis may have the potential to significantly suppress population growth and the damage caused by S. litura

Influence of leaf trichome type, and density on the host plant selection by the greenhouse whitefly, Trialeurodes vaporariorum (Hemiptera: Aleyrodidae)

Host selection by adult greenhouse whitefly Trialeurodes vaporariorum (Westwood) was assessed on two pelargonium plant cultivars, Pelargonium x domesticum (regal) and P. x hortorum (zonal) using Petri dish bioassay chambers in choice and no-choice tests. Plant characteristics which could influence the oviposition preference of the whitely i.e., type and density of trichomes on the abaxial leaf surface was determined. A strong host preference was observed for the regal compared to the zonal pelargonium by the adult whiteflies. In no-choice tests, adults laid a significantly higher number of eggs on regal than on zonal leaves both at 24 and 48 hours post-exposure, respectively. After exposure to the adult whitefly, the number of 42 eggs in choice tests were similar between cultivars at 24 hours, but were higher for regal at 48 and 72 hours. The total number of trichomes (sng: straight non-glandular + sg: straight glandular) per 0.50 cm2 44 was significantly less on regal (Mean ± SE sng + sg; 43.1 ± 1.5) than on zonal leaves (60.5 ± 1.2); however, the sng trichomes were significantly higher on the zonal (49.4 ± 0.96) than the regal leaves (28.6 ± 1.00). Also, the number of sg trichomes was slightly higher for the regal cultivar leaves compared to the zonal, being 14.4 ± 1.2 and 11.2 ± 0.5, respectively. Results suggest that the trichome density, type and the ability to express glandular exudates can affect adult whitefly Pelargonium cultivar preference and plays an important role in their host plant selection for oviposition

Gustatory Sensitivity and Food Acceptance in Two Phylogenetically Closely Related Papilionid Species: Papilio hospiton and Papilio machaon.

In herbivorous insects, food selection depends on sensitivity to specific chemical stimuli from host-plants as well as to secondary metabolites (bitter) and to sugars (phagostimulatory). Bitter compounds are noxious, unpalatable or both and evoke an aversive feeding response. Instead, sugars and sugar alcohols play a critical role in determining and enhancing the palatability of foods. We assumed that peripheral taste sensitivity may be related to the width of the host selection. Our model consists of two closely phylogenetically related Papilionid species exhibiting a difference in host plant choice: Papilio hospiton and Papilio machaon. The spike activity of the lateral and medial maxillary styloconic taste sensilla was recorded following stimulation with several carbohydrates, nicotine and NaCl, with the aim of characterizing their gustatory receptor neurons and of comparing their response patterns in the light of their different acceptability in feeding behaviour. The results show that: a) each sensillum houses phagostimulant and phagodeterrent cells; b) the spike activity of the gustatory neurons in response to different taste stimuli is higher in P. hospiton than in P. machaon; c) sugar solutions inhibit the spike activity of the deterrent and salt cells, and the suppression is higher in P. machaon than in P. hospiton. In conclusion, we propose that the different balance between the phagostimulant and phagodeterrent inputs from GRNs of maxillary sensilla may contribute in determining the difference in food choice and host range

Can plant resistance to specialist herbivores be explained by plant chemistry or resource use strategy?

At both a macro- and micro-evolutionary level, selection of and performance on host plants by specialist herbivores are thought to be governed partially by host plant chemistry. Thus far, there is little evidence to suggest that specialists can detect small structural differences in secondary metabolites of their hosts, or that such differences affect host choice or performance of specialists. We tested whether phytochemical differences between closely related plant species are correlated with specialist host choice. We conducted no-choice feeding trials using 17 plant species of three genera of tribe Senecioneae (Jacobaea, Packera, and Senecio; Asteraceae) and a more distantly related species (Cynoglossum officinale; Boraginaceae) containing pyrrolizidine alkaloids (PAs), and four PA-sequestering specialist herbivores of the genus Longitarsus (Chrysomelidae). We also assessed whether variation in feeding by specialist herbivores is attributable to different resource use strategies of the tested plant species. Plant resource use strategy was quantified by measuring leaf dry matter content, which is related to both plant nutritive value and to plant investment in quantitative defences. We found no evidence that intra-generic differences in PA profiles affect feeding by specialist herbivores. Instead, our results indicate that decisions to begin feeding are related to plant resource use strategy, while decisions to continue feeding are not based on any plant characteristics measured in this study. These findings imply that PA composition does not significantly affect host choice by these specialist herbivores. Leaf dry matter content is somewhat phylogenetically conserved, indicating that plants may have difficulty altering resource use strategy in response to selection pressure by herbivores and other environmental factors on an evolutionary time scal