Helopeltis antonii

H. antonii are often mistaken and misidentified with other Helopeltis species.[2] Thus, identifying the exact geographical range of H. antonii has become a difficult process. However, recent advances in species identification though DNA barcoding has made it much easier.[1] DNA barcoding is a rapid and relatively inexpensive identification technique that locates unique genetic markers in their DNA allowing for the accurate identification of not only H. antonii, but other species as well.[1]

Arousal consists of both chemical and tactile stimuli.[3] Pheromones play an important role in the chemical attraction of females for mating.[3] Although these chemical cues are important, physical cues comprise the bulk of mate attraction and arousal.[3] Males are the sole initiators for reproductive encounters. This first done through sexual identification of a female partner. Sexual identification is only possible when in close proximity of each other.[3] Once a female is located, the male makes contact with the female by gently probing her body with his antennae. Receptive females remain passive, permitting the male to proceed. In contrast, non-receptive females move to escape any further male interaction.[3]

Following the initial arousal, the process of mounting ensues. Males mount females on the posterior region of her body allowing the erect male rostrum to stroke the dorsal side of the female, just below the thoracic shield. This stroking behaviour quiets the female and allows for easier insertion of the male aedeagus into the female genital aperture. If insertion is not achieved the male begins a left to right stroking motion to aid in its insertion. Females can also kick or shake males off to prevent further progression of mating. When this occurs, males are quick to remount and re-attempt insertion of their aedeagus into the female genital aperture. Successful insertion leads to copulation.[3]

Once insertion has been established the male twists around in an end-to-end fashion to allow for copulation. Once in this end-to-end position, both the male and female remain still until copulation has completed. This can last anywhere from 10 minutes to 2 hours.[3]

Following copulation, they abruptly disjoin, however, detachment can be often difficult due to the males' twisted position. Once separated both the male and female begin to feed and clean their own genitals and antenna—this feeding and cleaning behaviour typically occurs within a few steps from the site of copulation.[3] Females do not respond to any other mating advances immediately following copulation.[3] However, females typically reproduce more than once during their lifetime.[5] Interspecific mating has been known to occur between Helopeltis species, specifically between H. antonii and H. theivora. However, their mating results in the production of unviable eggs.[6] The production of eggs following interspecific mating between H. antonii and H. bradyi has not been observed.[6] This ability and inability to engage in interspecific mating is due to the difference in genital structure between females.[6] Females of both H. antonii and H. theivora have sclerotized rings that are not fused, whereas, the females of H. bradyi have fused sclerotized rings in its genitalia. This difference acts like a “lock and key” model for genitalia.[6]

Although colouration is an important identifying feature of H. antonii it is subject to variation due to variations in temperature and sunlight exposure.[4] Red colour morphs tend to peak in abundance during October and reach their minimum abundance during February (for males) and June (for females).[4] Black colour morphs peak during June for both sexes.[4] A brownish-black colour morph is also seen within the population, but its abundance is low, and its frequency remains constant throughout the year.[4]

H. antonii feed on both native plants as well as agriculturally grown crops.[8] However, their availability changes with the seasons. This change in availability is due to the different growth cycles host plants experience throughout the year. As host plants enter their fruiting or flushing stages, they begin to have a higher rates of sap production and as a result become targeted by H. antonii.[8] In native, non-cultivated, habitats there appears to be a preference for certain types of host plants even when many others are present.[8] During January to February Annona is preferred, from March to April neem is preferred, from May to August papaya is preferred, and from September to December Singapore cherry is preferred.[8] In addition to the consumption of native plant species, agricultural “cash crops” such black pepper, cashew, cocoa, and tea as are often at high risk for consumption and damage due to their large-scale cultivation and ease of accessibility.[2] However, their feeding schedule on these is agricultural crops are more restricted based due to growing and harvest seasons.

Like the seasonal preference of plants, preference is also seen in consumption habits of fruits with respect to different plants. For example, in custard apples the immature fruits are preferred over the matured fruits. Whereas in the Singapore cherries there is no observed feeding preference for immature or mature fruits.[8]

Feeding requires the insertion of their stylet into the plant tissues. This insertion results in the secretion of saliva. Present within their saliva are toxic substances that cause death of plant tissues following feeding. However, the biochemical understanding of the toxin's toxicology and function within the saliva is poorly understood and is a site of current research.[9]

H. antonii are subject to both predation and parasitism via parasitoids.[10] Parasitoids of both nymph and adult morphs include Hymenoptera (Braconidae, Platygastridae) and Diptera (Sarcophagidae).[10] Predators are more extensive in diversity and consist of Hymenoptera (Formicidae, Vespidae), Coleoptera, Mantodea, and Odonata.[10]

Of specific interest and use are hymenopteran parasitoids, specifically, Telenomus cupis due to their high specificity and specialization on H. antonii eggs. The employment of these parasitoid specialists has significantly decreased the abundance of H. antonii eggs to effectively reduce their devastating impact on agricultural crops.[11] Additionally, these hymenopteran parasitoids are one of the few parasitoids that are active year-round.[11]

The combined use of pesticides and biological control agents are less effective in reducing the number of H. antonii within agricultural systems. This is because these pesticides also act against biological control agents—reducing their effectiveness. Additionally, the biological control agents tend to be more affected by pesticides than H. antonii.[10] Biological predators and parasitoids are more affected than H. antonii due to their increase locomotory abilities causing them to be exposed to larger amounts of the synthetic pesticides found on crops.[10] The extensive and prolonged use of pesticides and its lesser effect on H. antonii, when compared to its biological control agents, raises concerns regarding pesticide resistance. However, such evidence has yet to suggest the acquisition of pesticide resistance in H. antonii.[4]

Although feeding results in necrotic lesioning and desiccation, it is not the only factor that impacts yield. Following foraging, fungal pathogens can enter the wound tissues more readily and cause die-back of shoots and is the primary cause of inflorescence blight.[9] Even though fungal blight is a common occurrence in various plants, the wounds caused by H. antonii in plant tissues exacerbates and accelerates its effects.[9] Die-back from blight also limits the plant's ability to produce products and grow—further perpetuating yield loss.[9]