- Helopeltis antonii Signoret
- H. bradyi Waterhouse
- H. theivora Waterhouse
- Pachypeltis maesarum Kirkaldy
Family: Miridae, Order: Hemiptera
TMB is a major pest of cashew causing severe damage in several parts of the world. Among the four species attacking cashew, H. antonii is the dominant species. The pest has got potential to cause as high as cent per cent loss in yield.
- Adult H. antonii are slender, elongate, 6-8 mm long, reddish brown in colour, black head with reddish/ brownish/ blackish thorax and black and white abdomen. The nymphs of H. antonii are light brownish to brown in colour.
- H. bradyi closely resembles H. antonii, but has a minute colour variation in the hind femur and abdominal region. The nymphs are brownish in colour.
- H. theivora has longer antennae and yellowish pronotal ring and greenish white patch in the abdomen. Nymphs are greenish to greenish yellow in colour.
A pin-like knobbed scutellar process is present dorsally in both the nymphs (except first instar) and adults. Nymphs are translucent reddish brown having long antennae. The size of nymphs of H. antonii and H. bradyi are almost similar except slight variation in colour, whereas, the nymphs of H. theivora are comparatively smaller and slender.
(From left : H. antonii, H. bradyi, H. theivora and P. maesarum)
- Tiny eggs are inserted into tender shoots, stalks of inflorescence, leaf midribs and petioles, either singly or in groups of 2-6. Presence of a pair of minute silvery hair like unequal chorionic processes of 0.4-0.6 mm length projecting outside is indicative of the presence of each egg inside the plant tissues.
- The nymph hatches in 6-8 days, undergo five instars in a period of 8-14 days and develop as adults. The nymphs develop faster and survive better, when feed on immature fruits than flushes and panicles.
- The preoviposition and oviposition period of TMB range from 3-5 days and 5-10 days respectively. The adults survive even more than a month and the female bug can lay up to 259 eggs during its life time.
- In general, TMB activity is very less during monsoon period (June- September) and the pest build up commences during October- November synchronizing with the emergence of new flushes after the cessation of monsoon rains.
- The population reaches a peak during December-January, when the trees are in full bloom while, the pest activity is seen till May unitl harvest.
- But, the pest incidence may be noticed throughout the year in young plantations.
- The nymphs and adults suck the sap from the tender leaves, shoots, panicles, immature nuts as well as immature apples. Initially, water soaked lesions appear at the feeding sites, which turn scabby black in 2-3 days.
- Feeding also causes exudation of gummy substances from the plant parts. Later, the lesions coalesce and ultimately results in drying of shoots.
- The infestation on panicles results in blossom blight, wherein the flowers and stalks of panicles completely dry up.
- Upon severe damage, most of the flushes and panicles dry up and the tree develops a scorched appearance.
- Developing nuts and apples of all stages are attacked by TMB. As a result of injury, immature nuts drop off. If older ones are attacked, they survive with injury and attain maturity.
- Variety of plants are infested by tea mosquito bug, mostly by H. antonii and H. theivora.
- Important host plants include neem (Azadirachta indica), cocoa (Theobroma cacao), guava (Psidium guajava), drumstick (Moringa oleifera), cotton (Gossypium spp.), Singapore cherry (Muntingia calabura), black pepper (Piper nigrum), allspice (Pimenta dioica), henna (Lawsonia inermis), mahogany (Swietenia mahagoni), eucalyptus (Eucalyptus sp.), apple (Malus domestica), avocado (Persea americana), camphor (Cinnamomum camphora), cinchona (Cinchona sp.), cinnamon (Cinnamomum zeylanicum), grapes (Vitis vinifera), red gram (Cajanus cajan), tamarind (Tamarindus indica), tea (Camellia sinensis), pepper (Piper nigrum), cocoa (Theobroma cacao) etc. P. maesarum also infests Careya arborea, Pogostemon parviflora and on Leea sambucina.
- Apart from these, a few weed plants in the cashew plantations also support TMB during off season especially Chromolaena odorata, Calycopteris floribunda etc.
(From left : Neem, Singapore Cherry and Henna)
Proper surveillance and monitoring at regular intervals for damage symptoms during flusing, flowering and fruiting period of cashew as well as on importatn host plants present in the surroundings of cashew plantations are required so as to initiate the management measures.
Chemical control methods
- First round of insecticidal spray need to be given, whenever the incidence occurs at 5 – 10 % damage.
- Second spray may be repeated within 3 – 4 weeks and thrid spray can be given as and when required.
- If panicle damage is severe (beyond 50 %) further sprays can not help in increasing yield.
- Chemicals that can be sprayed in rotation are: lambda cyhalothrin (0.6 ml/lit), thiametoxam (0.2 g/lit) and acetamiprid (0.5 g/lit).
Host plant resistance
- All the released varieties are susceptible for TMB attack and there is no completely tolerant cashew type against TMB infestation.
- Under low to moderate pest incidence, variety ‘Bhaskara’ escapes TMB damage because of its mid season flowering nature.
- Though the eggs of Helopeltis spp. are laid deep and concealed, they are often attacked by a range of parasitoids including Telenomus cuspis (Platygasteridae), Erythmeles helopeltidis (Mymaridae), Chaetostricha sp. (Trichogrammatidae), Ufens sp. (Trichogrammatidae) and Gonatocerus sp. (Mymaridae).
- Among which, T. cuspis is the major parasitoid which could cause even up to 50 % egg parasitism in TMB during certain months.
- Nymphal parasitoid of genus Leiophron (Hymenoptera: Braconidae) and a parasitic mite namely, Leptus sp. (Erythraeidae) also kills TMB adults, but occurs at very low intensity.
- Mass rearing of any of the parasitoid could not be successful in laboratory since they are host specific, hence they can not be exploited for TMB control at present.
Telenomus cuspis parasitizing TMB eggs
- On the other hand, the predatory fauna include a wide number of spiders, reduviid bugs, ants, praying mantids, mantispid flies, robber flies, pentatomid bugs etc that exist in field especially under unsprayed condition can predate on several insect pests.
- The aggressive predators namely, red ants (Oecophylla smaragdina) actively predate on TMB and other pests of cashew, thus providing service to farmers in reducing the pest attack. Those trees having ant nests must be spared of insecticidal sprays so as to conserve them.
Telenomus sp. predating on TMB
- Specific strain of the entomopathogenic fungus, Beauveria bassiana (IIHR strain) is found effective to little extent against TMB during certain months.
- Presence of sex pheromone activity in female TMB is confirmed in studies conducted at DCR, wherein virgin TMB and mated female tend to attract males.
- The research is underway to identify the chemical nature of pheromone and to investigate the possiblity of synthesizing it so as to use under field conditions.