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Orius minutus
Orius minutus is a Palearctic species of minute pirate bug in the family Anthocoridae.[1] O. minutus is naturally distributed throughout Europe, western Russia, North Africa, China, Japan, and Siberia[1][2] The predatory bug was accidentally introduction into North America through plant material commerce and regular dispersal; the introduction of O. minutus is generally considered beneficial to the agricultural industry.[1][3][4] O. minutus is an important addition to the predator complex of many crops, and its role as a non-commercialized biological control agent highlights its unique contribution to pest management strategies.[1][3][4] DiagnosticsAdultsAdult females of O. minutus are larger (2.05-2.60 mm total length) and more broadly ovate (0.85-0.97 mm pronotal width) than males, who are slenderer (0.7-0.82 mm pronotal width) and possess thicker antennae.[1] The heads range from dark brown to black, all sporting yellow antennae.[1] The pronotum and scutellum are brownish-grey to brownish-black, with the hardened forewings yellowish brown.[1] The underside and hind legs are dark brown to black, with the front and middle legs yellow.[1] Lengths of golden setae adorn the dorsal side of the insect.[1] NymphsFifth instar nymphs of O. minutus are differentiated from other members of the genus Orius (e.g. O. tristicolor) by their broadly ovate body shape with one-third of the wing pad's tip a much darker colour than the rest of the dorsum.[1] The maximum width of the pronotum is 0.70 mm or greater.[1] It is difficult to differentiate between earlier instars; many members of the genus Orius are a creamy white colour prior to their fifth instar.[1] However, O. minutus are generally more robust and broader than other species.[1] Their eyes nearly touch the anterior margin of the pronotum.[1] The head is relatively short, with the protunum almost 1.5 times the width of the head.[1] ReproductionMatingO. minutus females are functionally monandrous.[5] Generally, females can not be inseminated by one mating;[5] only if the first mating fails will the females choose to mate with another male.[5] Females will refuse unwanted mating attempts by lifting their ovipositors and struggling;[5] such behaviours suggest females control the functional monandry.[5] The number of unique male partners does not affect fecundity, though mating with a single male decreases the hatching success of eggs.[5] Males are polygamous and can inseminate at least three females at a rate of one female per day;[5] the insemination ability of males persists for at least three copulations.[5] Unlike many members of Anthocoridae, traumatic insemination does not occur within O. minutus.[6] Males instead employ extragenital insemination to transfer spermatozoa into the female's body.[6] The male's needle-like flagellum is inserted intersegmentally between the female's abdominal segments without wounding or scarring her outer body;[6] the cone present on male genitalia assists in expanding the space between the female's lower abdominal segments.[6] Males possess a partially sclerotized copulatory tube to support and guide the flagellum into the female's sperm pouch.[6] The spermatozoa can remain within the sperm pouch weeks after depositing several eggs, suggesting the sperm pouch functions as a long-term storage organ.[6] Females may be able to store spermatozoa for their entire lifetime, a consequence of functional monandry.[6] An extragenital structure called the ectospermalege is located at the fourth segment of the female body.[6] Underneath the ectospermalege is the mesospermalege, a special endodermal pouch that receives the spermatozoa.[6] O. minutus females lack spermatheca, instead possessing a pair of pseudospermatheca at the base of their lateral oviducts;[6] the pseudospermatheca receives the spermatozoa, which transfers from the mesospermalege in the hemolymph.[6] PheromonesContact sex pheromones are present within the trails of O. minutus.[7] Trails left by mature virgin females aid males in locating a mate.[7] Males will linger on leaves exposed to trails left by mature virgin females, allowing males to locate conspecific females who had recently deposited trails on the plant.[7] Males will respond to the trails regardless of their mating experience, though only trails from mature females arrest males.[7] Females respond with weak arrestment to the leaves walked on by males, which could further assist in finding a mate.[7] Effect of temperatureAlthough O. minutus have a higher rate of reproduction at temperatures between 17 and 26 °C, they experience a decrease in lifetime fecundity at and above temperatures of 26 °C;[8] the reduction in fecundity at higher temperatures suggests that O. minutus are disadvantaged when experiencing wide ranges of temperatures.[4] Life historyO. minutus females overwinter fertilized, usually emerging from hibernation in the early spring.[1][8][9] Males can hibernate but are unlikely to survive the winter due to their lack of diapause and inadequate lipid accumulation.[1][10] Shortly after hibernation ends, eggs are deposited onto the base of developing flower buds or the midrib on the bottom of leaves.[1][11] O. minutus has five nymphal instars.[1] The developmental time from egg to adult depends on temperature and location, though adulthood is generally reached within 24 to 30 days.[1][9] O. minutus produce at least two generations annually, though up to four generations can be produced under ideal conditions.[1][9] Adults collected from early spring and mid-autumn suggest O. minutus is bivoltine.[1][9] DietO. minutus are generalist predators of small insects, including aphids, mites, thrips, whiteflies and scales.[1][3] Though chiefly predacious, O. minutus may occasionally feed on plant material and sap (e.g. the fluid produced by Eryngium campestre).[1] BehaviourForaging and flyingThough O. minutus initially flies out in random directions, the discovery of prey patches shifts their dispersal into foraging activity;[2] individuals that discover patches with a high prey density are hesitant to fly out from the patches.[2] Abiotic factors significantly influence this behaviour, with increased plant foraging behaviours correlating with high solar radiation and low humidity.[2] Both males and females are diurnal fliers, though females engage in less flight activity than males.[2] DiapauseThe critical photoperiod for inducing diapause is between 14.5-9.5D and 15L-9D at 22 °C, corresponding to late summer in many regions occupied by O. minutus.[10] During diapause, the insects do not copulate, and the female's ovaries remain small until the following spring.[10] Adult females do not enter diapause regardless of short day length if their nymphal stages were spent under long day length.[10] Adult diapause is not induced in males due to a shortage of lipid accumulation.[10] References
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