Demographic parameters of Helopeltis antonii Signoret ( Heteroptera : Miridae ) on neem , cocoa and henna

Helopeltis antonii is a polyphagous pest causing considerable economic damage for cashew in South India. Relative multiplication of H. antonii was studied on its three important alternate host plants; neem, cocoa and henna. Life tables and population parameters for the mirid were constructed based on unlimited food condition and a natural enemy-free environment. The preoviposition period was between 19 to 23, 20 to 23 and 17 to 21 days of pivotal age, respectively on neem, cocoa and henna. The survivorship (lx) of H. antonii for three hosts shows similar pattern with high mortality occurring during egg, nymphal growth particularly in the early instar which then gradually decreases throughout the life span. The life expectancy (ex) of H. antonii declined gradually with the advancement of growth development in all three host plants. The net reproductive rate indicating the total female births (Ro) was 43.8, 45.9 and 16.1; the population increased with a intrinsic rate (rm) of 0.1425, 0.1505 and 0.1218: and finite rate (λ) of 1.1531, 1.1624 and 1.1295 female per day and a generation was completed in 26.52, 25.42 and 22.81 days on neem, cocoa and henna, respectively. Percent contribution of different growth stages in stable age-distribution revealed that the immature stages (eggs and nymphs) contributed maximum.

In neem, the nymphs and adults of H. antonii suck the sap from the shoots, resulting in lesions that coalesce and become necrotic with gummosis (Sundararaju and Sundarababu, 1996).The affected tree is witnessed as burnt-up appearance during severe outbreak condition.A summary of feeding damage and visible symptoms on cocoa is given by Stonedahl (1991).Typical feeding damage appears as a discoloured, necrotic area or lesion around the point of entry of the labial stylets into the plant tissue that becomes darker with age as the tissue around the puncture dies.Infestations during the early stages of fruit often set result in immature fruit drop.Damage on pods appears as dark, circular lesions usually hardening as scars on the husk.Heavy infestations can result in pod malformation and premature drop.Brunt-up appearance can be distinguished in L. alba due to damage by H . antonii *Corresponding author.E-mail: sreeku08@gmail.com.

feeding (Figures 1 to 3).
Life table parameters are important in the measurement of population growth capacity of species under specified conditions.These parameters are also used as indices of population growth rates responding to selected conditions and as bioclimatic indices in assessing the potential of a pest population growth in a new area.Fertility life tables are appropriate to study the dynamics of insect populations as an intermediate process for estimating parameters related to the population growth potential, also called demographic parameters.Earlier life table studies of H. antonii was performed on cashew (Siswanto et al., 2008); neem, guava and cashew (Sundararaju and Sundarababu, 1998).
Life table studies have several applications including analyzing population stability and structure, estimating extinction probabilities, predicting life history evolution, detecting outbreak in pest species, and examining the dynamics of colonizing or invading species.Life table information may also be useful in constructing population models and understanding interactions with other insect pests and natural enemies.The objective of present study is to develop life history information on H. antonii on the important alternate hosts viz., neem, cocoa and henna and to determine the population parameters including the survivorship and rate of increase of H. antonii population on these host plants.This information could be extremely valuable for the future development of IPM programs against H. antonii.Demographic study was conducted to provide information on the life table of H. antonii fed on neem, cocoa and henna.Population growth parameters pertinent to this species are furnished in the present study.

MATERIALS AND METHODS
To construct the life table, the culture of H. antonii was maintained under laboratory conditions in Department of Entomology, Directorate of Cashew Research, Puttur, Karnataka.Male and Female TMB, H. antonii were collected using long test tubes from cashew fields.Nylon mesh sleeve cages (170 cm height x 30 cm diameter) were used to confine paired adult bugs on tender flushing shoots of neem, cocoa and henna in the field.During the study period, range of field temperature was 16 to 38°C, humidity 90 to 98%, monthly rainfall 0 to 1187.8 mm and sunshine was 0.8 to 8.8 h.Both ends of the cage were firmly tied to prevent the insects from escaping.The shoots were kept in their natural position by tying the upper part of the sleeve cage to a stake and lower part to the twigs.The sleeve cages were labeled with oviposition date and precautions were taken to prevent ants from attacking the mirids.The presence of a pair of fine terminal respiratory filaments projecting from the surface of the plant tissue was indicative of the presence of eggs embedded in the bark (Figure 3a).The caging was done in the laboratory from fifth to seventh day after oviposition to prevent nymphal migration.Immediately after hatching the 20 nymphs (Figure 2) of 5 batches each were individually reared on neem, cocoa and henna in nymphal rearing cages (size: 15×15×20 cm and thickness: 18 gauge) (Sundararaju and John, 1992).Nymphal rearing cages consisted of four glass vials of 5 ml capacity fixed on a small aluminum stand with a handle of 15 cm height fixed at the centre.The fresh neem and henna shoots kept in water filled vial were supplied in alternate days as feed.In case of cocoa, nymphs were individually reared on cocoa pods (as nymphs shown high mortality on cocoa shoots).The presence of exuviae was used to determine nymphal instars of the insect.In the rearing cage on the two sides, provisions were made to fix with cloth sleeve in order to facilitate the removal of adults after final moulting.
The mated adult females were reared from egg stage on respective hosts and allowed to oviposit in the same host plant, that is, the adults that emerged on particular day were paired and released in separate nylon mesh sleeve cages (170 cm height × 30 cm diameter) in field.Fecundity of females was recorded until all of them died.The total number of eggs laid on each day was recorded for each subgroup.Then, the number of eggs laid per female was dived by 1.80 (Female (F): Male (M) ratio = 1:0.80)for neem, 1.1 (F: M = 1:1) for cocoa, 1.67 (F: M = 1:0.67)for henna in order to get the number of female (mx).Observations from hatching of eggs till the emergence and death of adults were recorded daily which provided the values for life table (lx).Life tables were constructed according to the methods of Birch (1948), Howe (1953) and Atwal and Bains (1974).Stable age distribution was worked out by observing the population schedule of birth and death rate (mx and lx) when grown in limited spare.Life expectancy at age x (ex) gives the average remaining lifetime for an individual (Carey, 1993).Life expectancy was computed by using the method suggested by Deevey (1947) and Atwal and Bains (1974).

RESULTS AND DISCUSSION
The survivorship (lx) of H. antonii for three hosts (Figure 4) in general shows similar pattern with high mortality occurring during egg and nymphal stages particularly in the early instar which then gradually decreases throughout the life span.This survivorship curve which indicates a modest rate of mortality during early life stages and comparatively a gradual reduction as it approached adulthood, the population assumed a near Type III diagonal survivorship curve following the classification of Pearl (1928); Schowalter (2006) and Speight et al. (1999).The H. antonii reared on cashew nearly exhibited Type II age-specific survivorship curve (Siswanto et al., 2008).
Close perusal of the figures (Figures 5 to 7) indicates that preoviposition period was between 19 to 23, 20 to 23 and 17 to 21 days of pivotal age on neem, cocoa and henna, respectively.The female contributed the highest number of progeny (mx) on 27, 26 and 23 days of life (along with adult emergence), respectively on neem, cocoa and henna.The results of Siswanto et al. (2008) showed that H. antonii fed on cashew laid highest numbers of eggs on 36 days.It would be plausible that insect's growth, longevity and reproduction could be influenced by their food sources (hosts plants) and environmental conditions (Satpute et al., 2005;Ellers-Kirk and Fleischer, 2006).
The H. antonii showed higher Ro, r m and λ values and lower T (than neem) and DT on cocoa pods.It is generally presumed that shorter development time and greater reproduction on a host reflect the suitability of the plant tested (Van Lenteren and Nolbus, 1996).Also, this has been demonstrated in cotton where shorter generation time (T) favoured higher reproduction fitness (Trichilo and Leigh, 1985).
In spite of lower generation time T, the r m value was low on henna because of very low Ro value, i.e, H. antonii can multiply more rapidly on cocoa and neem than on henna and also sustained under unfavourable conditions on both the host plants.H. antonii has a fine λ value (1.1295) on henna; suggesting the importance of this host plant for the pest.Insect's growth, longevity and reproduction could be influenced by their food sources (host plants or host preys) (Siswanto et al., 2008).Life tables giving data on the rm of a particular species provide insight into the characteristic life patterns of different species (Satpute et al., 2005).There is a range of innate capacity for individual of a population (Dewitt, 1954;Gill et al., 1989).
In the present investigation, the contribution made by different developmental stages viz., eggs, nymphs and adults of H. antonii towards stable age distribution was 57.5, 36.6 and 5.9% on neem; 60.82, 32.98 and 8.24% on cocoa; and 57.85, 36.42 and 5.71% on henna, respectively.The life expectancy data of H. antonii (Tables 2 to  4) on neem, cocoa and henna indicates that it declined gradually with the advancement of development.Life expectancy increases for individuals who survive their risky egg hatching period.
H. antonii is a polyphagous insect which feeds on various host plants.Cashew is one of the major host plants apart of neem, cocoa and henna.H. antonii feeds particularly on the young and succulent parts of cashew.When cashew plants do not have enough reserved food sources for the insects in the area during the lean period in cashew (May to September) would migrate to these alternate host plants.It showed apparent in the study sites as alternate host plants were found at the vicinity of the cashew plantation including cocoa trees.This suggests that appropriate management measures should be taken especially during vulnerable stages of cashew crop (flowering and fruiting period) before the onset of population build-up of H. antonii.

Conclusion
The demographic parameters obtained from H. antonii reared on three host plants under laboratory conditions are useful for the assessment of host plant quality.Intrinsic rate of increase and mean generation time reflect the suitability of the host plant.Meanwhile, this study provides a foundation regarding the host range of H. antonii, and as such will be useful to pest management.The host plants examined in this study are all

Figure 3 .Figure 4 .
Figure 3.(b) Eggs deposited on cocoa shoots and (c) adult bug feeding on cocoa pod.

Table 1a .
Life table of H. antonii on neem, cocoa and henna.

Table 1b .
Determination of rm value for H. antonii on neem.

Table 1c .
Determination of rm value for H. antonii on cocoa.

Table 1d .
Determination of rm value for H. antonii on henna.

Table 2 .
Life table for computing life expectancy of H. antonii reared on neem.