Attachment ability of females and males of the ladybird beetle Cryptolaemus montrouzieri to different artificial surfaces

Parasitoid attachment ability and the host surface wettability

Climbing animals such as geckos and arthropods developed astonishing adhesive mechanisms which are fundamental for their survival and represent valuable models for biomimetic purposes. A firm adhesion to the host surface, in order to successfully lay eggs is necessary for the reproduction of most parasitoid insects. In the present study, we performed a comparative investigation on the attachment ability of four parasitoid species (the egg parasitoid Anastatus bifasciatus (Eupelmidae), the aphid parasitoid Aphidius ervi (Braconidae), the fly pupal ectoparasitoid Muscidifurax raptorellus (Pteromalidae) and the pupal parasitoid of Drosophila Trichopria drosophilae (Diapriidae)) with hosts characterized by a surface having different wettability properties. The friction force measurements were performed on smooth artificial (glass) surfaces showing different contact angles of water. We found that attachment systems of parasitoid insects are tuned to match the wettability of the host surface. Sexual dimorphism in the attachment ability of some tested species has been also observed. The obtained results are probably related to different microstructure and chemical composition of the host surfaces and to different chemical composition of the parasitoid adhesive fluid. The data here presented can be interpreted as an adaptation, especially in the female, to the physicochemical properties of the host surface and contribute to shed light on the coevolutionary processes of parasitoid insects and their hosts.

The tight attachment achieved by the male discoidal setae is possibly a counter-adaptation to the grease layer on female integument surfaces in green dock beetles

Green dock beetles Gastrophysa viridula exhibit sexual dimorphism in tarsal attachment setae: females have only pointed, lanceolate and spatula-like setae, while males additionally possess discoidal ones. The sexual dimorphism is probably attributed to the necessity of male discoidal setae to adhere to the smooth back of the female during copulation. We aimed to understand its possible mechanism of attachment with G. viridula. Pull-off forces of both females and males were measured on (i) alive females, (ii) dead and dried females, and (iii) resin replicas of fresh females. The attachment ability tended to increase on dead and replicated female surfaces in both sexes, which indicates that the epicuticular grease layer on the integument of alive intact beetles decreases the attachment. This tendency was prominent in females. The present study clearly showed that in G. viridula discoidal setae enable the males to adhere stronger to female surfaces. The divergent performance found between the sexes differing in their setal composition is probably caused by the stiffness difference between the setae types and by the specific shape of the setal tips. A peculiar reproductive biology in G. viridula is probably attributed to this remarkable divergence of labour in their attachment pads between the sexes.

Effect of Leaf Trichomes in Different Species of Cucurbitaceae on Attachment Ability of the Melon Ladybird Beetle Chnootriba elaterii

This study investigates the attachment ability of the oligophagous melon ladybird beetle Chnootriba elaterii to leaves of several Cucurbitaceae species. Using cryo-SEM, we described adult and larva tarsal attachment devices and leaf surface structures (glandular and non-glandular trichomes) in Citrullus lanatus, Cucumis melo, Cucumis sativus, Cucurbita moschata, Cucurbita pepo, Ecballium elaterium, Lagenaria siceraria and Luffa aegyptiaca. Using traction force experiments and centrifugal force tests, we measured the friction force exerted by females and larvae on plant leaves. We observed that Cucurbitaceae glandular trichomes do not affect insect attachment ability at both developmental stages, suggesting some adaptation of C. elaterii to its host plants, while non-glandular trichomes, when they are dense, short and flexible, heavily reduce the attachment ability of both insect stages. When trichomes are dense but stiff, only the larval force is reduced, probably because the larva has a single claw, in contrast to the adult having paired bifid dentate claws. The data on the mechanical interaction of C. elaterii at different developmental stages with different Cucurbitaceae species, combined with data on the chemical cues involved in the host plant selection, can help to unravel the complex factors driving the coevolution between an oligophagous insect and its host plant species.

Self-righting physiology of the ladybird beetle Coccinella septempunctata on surfaces with variable roughness

Insects such as cockroaches and locusts self-right swiftly to reduce chances of being attacked by predators. Compared to these insects, ladybirds have shorter legs hidden inside highly domed elytra so self-righting is of great challenge if using strategies of abdominal arching and/or leg swinging. Specifically, ladybirds live in over-ground environment with clusters of vegetation so they are prone to self-right from various natural substrates, such as soil, bark, and leaves. However, self-righting strategies under such complicated environment packed with multiple surfaces remain elusive. In this combined experimental and theoretical study, we examined and quantified self-righting physiology of ladybirds (Coccinella septempunctata) on surfaces with varying roughness. Most ladybirds self-right in 15.00 s with a success rate of ~100.00% within 3 attempts using either legged or winged strategies, and the self-righting strategy is strongly associated with the surface roughness. Righting on a coarser board (R_a = 124.62 μm) is performed by swinging the legs to attach and hook the protrusions on the rough surface. However, if self-righting occurs on a smooth surface (R_a = 6.69 μm), both the elytra and hind wings deploy to alter the body orientation to roll over. Considering the effect of surface roughness, we analyzed the self-righting mechanism by a mathematical model, and uncovered that contact status between the claw and surface microstructures affected the arm of force required to self-right, which leads to the binary strategic selection. Our quantification of self-righting on diverse surfaces not only deepens understanding of ladybird's self-righting but may inspire new means of evaluating its environmental adaptability.

Variation of attachment ability of Nezara viridula (Hemiptera: Pentatomidae) during nymphal development and adult aging

The present investigation reports data on the attachment ability of the Southern green stink bug Nezara viridula (Hemiptera: Pentatomidae), a relevant pest in the world, along its whole life cycle. Using a centrifugal force tester, we evaluated a) the differences in the attachment ability among the four active nymphal developmental instars (N2-N5 nymphs) and adult to hydrophilic glass, showing an increased attachment ability during ontogenesis, owing to increased pulvilli size and efficiency; b) the possible role of growth and body shape on insect attachment ability on hydrophilic glass during the intermoult period, revealing that N. viridula nymphs attach stronger (higher safety factor) in the first part of the intermoult period; c) the age-specific differences in the attachment ability of adults of both sexes on hydrophilic glass, showing the best performance at an intermediate age, in agreement with a higher proportion of resilin in comparison with younger or older insects; d) the difference in attachment ability on hydrophilic vs. hydrophobic glass along the insect development, revealing a strong effect of surface hydrophobicity on reducing the attachment of N. viridula nymphs and adults. The results on the attachment ability of a hemimetabolous insect along its life cycle are relevant because they 1) shed light on different adaptations of attachment pads in relation to insect size, shape and age; 2) deepen the knowledge on the functional morphological adaptations, thus potentially contributing to the development of suitable control systems for this important pest insect.

Role of Fruit Epicuticular Waxes in Preventing Bactrocera oleae (Diptera: Tephritidae) Attachment in Different Cultivars of Olea europaea

The olive fruit fly Bactrocera oleae (Diptera: Tephritidae) is the major pest of cultivated olives (Olea europaea L.), and a serious threat in all of the Mediterranean Region. In the present investigation, we demonstrated with traction force experiments that B. oleae female adhesion is reduced by epicuticular waxes (EWs) fruit surface, and that the olive fruit fly shows a different ability to attach to the ripe olive surface of different cultivars of O. europaea (Arbequina, Carolea, Dolce Agogia, Frantoio, Kalamata, Leccino, Manzanilla, Picholine, Nostrale di Rigali, Pendolino and San Felice) in terms of friction force and adhesion, in relation with different mean values of olive surface wettability. Cryo-scanning morphological investigation revealed that the EW present on the olive surface of the different analyzed cultivars are represented by irregular platelets varying in the orientation, thus contributing to affect the surface microroughness and wettability in the different cultivars, and consequently the olive fruit fly attachment. Further investigations to elucidate the role of EW in olive varietal resistance to the olive fruit fly in relation to the olive developmental stage and environmental conditions could be relevant to develop control methods alternative to the use of harmful pesticides.