Selecting a suitable oviposition site is crucial to the fitness of female insects because it determines the successful development of their offspring. During the oviposition process, an insect must use cues from the external environment to make an appropriate choice of where to lay eggs. Generalist insects can detect and react to a plethora of cues, but are under selection pressure to adopt the most reliable ones to override noise and increase efficiency in finding hosts. The oriental fruit fly, Bactrocera dorsalis (Hendel), is a generalist that utilizes a multitude of fruits as oviposition sites. However, the identity and nature of oviposition stimulants for B. dorsalis is not well known. Recently, we identified a volatile compound γ-octalactone that elicits an innate oviposition response in B. dorsalis. We screened 21 EAD-active volatiles, identified from mango, for their oviposition stimulant activity. 1-Octen-3-ol, ethyl tiglate, and benzothiazole instigated oviposition in gravid B. dorsalis females. Flies deposited most of their eggs into pulp discs with oviposition-stimulants, and only a small fraction of eggs were laid into control discs. In a binary choice oviposition assay, 95.1, 93.7, and 65.6 % of eggs were laid in discs treated with 1-octen-3-ol, ethyl tiglate, and benzothiazole, respectively. Single plate two-choice assays proved that oviposition-stimulants were crucial in oviposition site selection by gravid female B. dorsalis. In simulated semi-natural assays, gravid B. dorsalis females accurately differentiated between fruits with and without 1-octen-3-ol, ethyl tiglate, and γ-octalactone by laying more eggs on the treated fruit. However, benzothiazole did not elicit an increase in oviposition when presented in this context. Our results suggest that the identified oviposition-stimulants are 'key' compounds, which the flies associate with suitable oviposition sites.

The oriental fruit fly, Bactrocera dorsalis, is an economically damaging, polyphagous pest of fruit crops in South-East Asia and Hawaii, and a quarantine pest in other parts of the world. The objective of our study was to identify new attractants for B. dorsalis from overripe mango fruits. Headspace samples of volatiles were collected from two cultivars of mango, 'Alphonso' and 'Chausa', and a strong positive behavioral response was observed when female B. dorsalis were exposed to these volatiles in olfactometer bioassays. Coupled GC-EAG with female B. dorsalis revealed 7 compounds from 'Alphonso' headspace and 15 compounds from 'Chausa' headspace that elicited an EAG response. The EAG-active compounds, from 'Alphonso', were identified, using GC-MS, as heptane, myrcene, (Z)-ocimene, (E)-ocimene, allo-ocimene, (Z)-myroxide, and γ-octalactone, with the two ocimene isomers being the dominant compounds. The EAG-active compounds from 'Chausa' were 3-hydroxy-2-butanone, 3-methyl-1-butanol, ethyl butanoate, ethyl methacrylate, ethyl crotonate, ethyl tiglate, 1-octen-3-ol, ethyl hexanoate, 3-carene, p-cymene, ethyl sorbate, α-terpinolene, phenyl ethyl alcohol, ethyl octanoate, and benzothiazole. Individual compounds were significantly attractive when a standard dose (1 μg on filter paper) was tested in the olfactometer. Furthermore, synthetic blends with the same concentration and ratio of compounds as in the natural headspace samples were highly attractive (P < 0.001), and in a choice test, fruit flies did not show any preference for the natural samples over the synthetic blends. Results are discussed in relation to developing a lure for female B. dorsalis to bait traps with.

Innate recognition templates (IRTs) in insects are developed through many years of evolution. Here we investigated olfactory cues mediating oviposition behavior in the oriental fruit fly, Bactrocera dorsalis, and their role in triggering an IRT for oviposition site recognition. Behavioral assays with electrophysiologically active compounds from a preferred host, mango, revealed that one of the volatiles tested, γ-octalactone, had a powerful effect in eliciting oviposition by gravid B. dorsalis females. Electrophysiological responses were obtained and flies clearly differentiated between treated and untreated substrates over a wide range of concentrations of γ-octalactone. It triggered an innate response in flies, overriding inputs from other modalities required for oviposition site evaluation. A complex blend of mango volatiles not containing γ-octalactone elicited low levels of oviposition, whereas γ-octalactone alone elicited more oviposition response. Naïve flies with different rearing histories showed similar responses to γ-octalactone. Taken together, these results indicate that oviposition site selection in B. dorsalis is mediated through an IRT tuned to γ-octalactone. Our study provides empirical data on a cue underpinning innate behavior and may also find use in control operations against this invasive horticultural pest.

Commensal bacteria influence many aspects of an organism's behaviour. However, studies on the influence of commensal bacteria in insect mate-selection are scarce. Here, we present empirical evidence that commensal bacteria mediate mate-selection in the Oriental fruit fly, Bactrocera dorsalis. Male flies were attracted to female flies, but this attraction was abolished when female flies were fed with antibiotics, suggesting the role of the fly's microbiota in mediating mate-selection. We show that male flies were attracted to and ejaculated more sperm into females harbouring the microbiota. Using culturing and 16S rDNA sequencing, we isolated and identified different commensal bacteria, with Klebsiella oxytoca being the most abundant bacterial species. This preliminary study will enhance our understanding of the influence of commensal bacteria on mate-selection behaviour of B. dorsalis and may find use in devising control operations against this devastating pest.

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1. Frequently changing climatic conditions can cause recurring droughts which often subject plants to tremendous amounts of stress, leaving biologists to wonder about its impact on the associated herbivores and their interactions with host plants. 2. The present study was aimed at assessing the impact of low moisture stress on herbivore‐plant interactions using tomato and its associated herbivores (leaf miner, Tuta absoluta and sap feeder, Bemisia tabaci). 3. The leaf miner T. absoluta preferred tomato plants exposed to moderate drought stress compared to severely drought stressed or healthy plants while the sap feeder B. tabaci preferred healthy tomato plants that were irrigated regularly over others. Our study uncovers few intriguing aspects of low moisture stress on herbivore‐host interactions and also highlights that this influence may vary depending upon the herbivore feeding guild. 4. The volatile profiles of tomato plants were found to differ significantly when subjected to varied degrees of low moisture stress. Such changes in plant's volatile emissions may in turn alter its associated herbivore's behavioural perspective as observed in T. absoluta and B. tabaci. 5. Reduced amounts of caryophyllene, humulene, 3‐carene, myristic acid, and γ‐butyl‐γ‐butyrolactone might be what aids T. absoluta and B. tabaci in gauging the drought stress status of a host plant. Further, the presence of chemical cues such as α‐pinene, m‐cymene, and ethyl benzaldehyde might signal T. absoluta moths of severely stressed plants. Similarly, the presence of undecane, ethyl benzaldehyde, n‐hexadecanoic acid might aid whiteflies in identifying plants reeling under low moisture stress.

Amylase is one of the important digestive enzymes involved in hydrolysis of starch. In this paper, we describe a novel approach to study the interaction of amylase enzyme with gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) and checked its catalytic function. AuNPs are synthesized using citrate reduction method and AgNPs were synthesized using biological route employing Ficus benghalensis and Ficus religiosa leaf extract as a reducing and stabilizing agent to reduce silver nitrate to silver atoms. A modulatory effect of nanoparticles on amylase activity was observed. Gold nanoparticles are excellent biocompatible surfaces for the immobilization of enzymes. Immobilized amylase showed 1-to 2-fold increase of activity compared to free enzyme. The biocatalytic activity of amylase in the bioconjugate was marginally enhanced relative to the free enzyme in solution. The bioconjugate material also showed significantly enhanced pH and temperature stability. The results indicate that the present study paves way for the modulator degradation of starch by the enzyme with AuNPs and biogenic AgNPs, which is a promising application in the medical and food industry.

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